DRAFT FOR INTERNAL USE ONLY DO NOT CITE/DISTRIBUTE THE IPCC ASSESSMENT OF KNOWLEDGE RELEVANT TO THE INTERPRETATION OF ARTICLE 2 OF THE UN FRAMEWORK CONVENTION ON CLIMATE CHANGE: A SYNTHESIS REPORT 1995 Draft Summary for Policymakers 1. Introduction 1.1 The UN Framework Convention on Climate Change recognizes that human activities could alter the Earth's climate. Its ultimate objective as expressed in its Article 2 is: "... stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change and to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner". 1.2 A determination of what concentrations of greenhouse gases are "dangerous" is a policy judgement. This summary provides an assessment of scientific and technical information for policymakers in their consideration of Article 2. It is based on the IPCC reports of 1994 and 1995. 2. Is There Evidence that Human Activities are Changing the Climate? 2.1 Human activities are causing increases in atmospheric concentrations of greenhouse gases, particularly carbon dioxide and methane, and of aerosols (tiny airborne particles) . Greenhouse gases warm the atmosphere while aerosols tend to cool it. The cooling effect of aerosols is regional because of the regional nature of their distributions. 2.2 Comparing the observed change in the global mean temperature with model simulations suggests that the observed increase over the last century (0.3 C - 0.6 C) is unlikely to be entirely due to natural causes and that a pattern of climatic response to human activities is identifiable in the climatological record. It is more difficult to determine whether global precipitation has changed; increases are evident in some places but not in others. On a global scale, there is little evidence of sustained trends in variability or extremes of weather events such as hurricanes and floods. On regional scales, there is clear evidence of changes in them. 3. How is Climate Projected to Change in the Absence of Mitigation Policies? 3.1 Based on inputs such as population, economic growth, land-use, technological change and energy availability, and assuming no climate change policies, the IPCC developed a range of emissions scenarios - the so-called IPCC IS 92 scenarios. For these scenarios, carbon dioxide emissions in the year 2100 are projected to be in the range of about 6 GtC per year (for low population projections), similar to current emissions, to as much as 36 GtC per year. Cumulative emissions of carbon dioxide for the same scenarios for the period 1990-2100 would range from 700 to 2080 GtC (compared to 240 GtC for 1860-1994). The wide range in the projections reflects different prevailing views on population and economic growths and other factors. 3.2 Climate models, using the IS 92 scenarios, project an increase in the global mean temperature of 0.8 C to 3.5 C by 2100, the range in the projections arising from uncertainties in climate processes and future greenhouse gas emissions. (The range would be 0.8 C-4.6 C if aerosols were excluded in the models.) However, only 50-70% of the eventual equilibrium temperature change would have been realized by that time. These temperature changes are expected to be accompanied by changes in the regional and temporal patterns and intensity of rainfall (increased tendency for both floods and droughts) and, by the year 2100, an increase in the global mean sea-level of 0.1 to 0.8 m (0.1 to 1.2 m if aerosols were excluded in the models). These projections indicate changes more rapid than any experienced in the last 10,000 years, the current interglacial when modern society has evolved. Even if atmospheric concentrations of the greenhouse gases were immediately stabilized, society would be committed to a further increase in temperature of 0.5 C-2 C. 3.3 Ability to project climate changes at the regional level remains low. 4. How Vulnerable are Ecological and Socio-Economic Systems and Human Health to Climate Change? 4.1 Quantitative projections of the impacts of the magnitude and rate of climate change on any particular ecological or socio-economic system are difficult because (i) regional scale climate change predictions are more uncertain than global climate change, (ii) our understanding of many critical processes is limited and (iii) the systems areinfluenced by multiple environmental and non- environmental stresses. Various aspects of climate affect ecosystems and socio-economic systems differently: some systems are sensitive to a change in mean climate, some to changes in the frequency and severity of extreme weather events, some to the rate of change and some to changes in climate variability. 4.2 Most impact studies have only dealt with how systems would respond to a climate change resulting from a (arbitrary) doubling of atmospheric carbon dioxide concentration over its pre-industrial level. Few have considered the evolving responses of systems to steadily increasing greenhouse gas concentrations over the corresponding period, and fewer still have examined the consequences of greenhouse gas increases beyond this arbitrary doubling. 4.3 While there would be some beneficial effects of climate change, there would be many adverse effects, with some being potentially irreversible, e.g., loss of biological diversity and land. While population increases and human decisions about land use and harvesting intensities potentially represent the greatest pressures on most terrestrial and marine ecosystems in the foreseeable future, climate change represents an important additional stress factor which could result in the following impacts. a. Natural ecosystems: The boundaries of most ecosystems would shift with possible loss of biological diversity and affecting the goods and services ecosystem types (e.g., forests, grasslands, savannah) provide society. For example: even a rate of temperature change as low as 0.1 C per decade (the lower end of the range of IPCC projections), if sustained for a century, would result in significant loss of forest tree species as they cannot migrate quickly enough to keep pace; changes of a few degrees in temperature can result in the loss of species in the upper elevations of montane systems because no migration would be feasible for them as climate warms. b. Food security: There may be significant adverse consequences for food security in some regions of the world even though the current assessment has confirmed the 1990 IPCC conclusion that the aggregate effects of climate change on global agricultural production may be small to moderate. Studies tend to show more negative impacts for areas in the tropics where many of the world's poorest people live and where individuals are at greatest risk of hunger. c. Sustainable economic development: Sustainable economic development in some countries will be threatened by loss of habitat, increases in human diseases and loss of life. Some human habitats are likely to be destroyed by sea level rise and possible change in extreme weather events, causing migration of populations and placing additional stresses on already stressed social and political systems. For human health, a critical issue is the projected increase in the incidence of vector-borne diseases such as malaria, especially in tropical and subtropical countries, and increased periods of severe heat stress in temperate zones. 4.4 Because both the rate and magnitude of climate change are important, the rates of change of atmospheric concentrations of greenhouse gases may be as important as stabilization levels. Non-disruptive adaptation in the structure and functioning of natural ecosystems and agriculture and other socio- economic systems is more likely, but not assured, with a slow rate of climate change. Rapid changes, on the other hand, may preclude non-disruptive adaptation. 4.5 Adaptation strategies for managed systems such as agriculture and water supply are generally improving because of technological advances. These advances, however, are not available in many parts of the world. In contrast, measures to assist adaptation in unmanaged ecosystems, such as provision of migration corridors, are not well developed. 4.6 The vulnerability of human health and socio-economic systems, and to a lesser extent of ecological systems, depends upon economic circumstances and institutional infrastructure. This implies that systems are typically more vulnerable in developing countries where technologies are fewer and less advanced and financial resources more scarce. 4.7 Incorporation of environmental concerns into resource-use and development decisions will enhance society's resilience to climate change. 5. How do Emissions Relate to Levels of Stabilization of Greenhouse Gases? 5.1 The Convention in Article 3 provides that the type of strategy used in reaching its objective should be comprehensive, covering all relevant sources, sinks and reservoirs of greenhouse gases. The individual radiative forcing (radiative forcing drives climate change) due to increases in the concentrations of different greenhouse gases - CO2, CH4, N2O and halocarbons and thereby implicitly stratospheric ozone - can be combined and the total expressed in terms of an "equivalent" CO2 concentration. This concept is helpful in analysing the comprehensive approach. 5.2 Carbon cycle models can be used to estimate emission profiles and cumulative emissions of carbon dioxide for various stabilization levels. Such estimates have been made for an illustrative set of CO2 stabilization levels ranging from 450 ppmv to 750 ppmv. Table 1 shows the cumulative emissions. The cumulative emissions could be distributed in different ways over the time until stabilization: higher emissions earlier with lower emissions later or vice versa, for example. 5.3 The cumulative emissions in table 1 are illustrated for two cases: with and without projected increases in methane and nitrous oxide until 2050 in accordance with IS 92a scenario. Accepting, for example, continued growth in the emissions of these gases would significantly reduce the room for cumulative emissions of carbon dioxide for a given stabilization level of "equivalent" carbon dioxide. 5.4 Table 2 shows the cumulative emissions for all IS 92 scenarios. These figures together with table 1 suggest that to stabilize "equivalent" carbon dioxide at 750 ppmv would require emissions to be much lower than the central IS 92a (and IS92b) scenarios. Stabilization of "equivalent" carbon dioxide at 550 ppmv (about twice the pre-industrial level) or lower would require emissions to be lower than any of the IS 92 scenarios except IS 92c (where a low increase of world population to 6.3 billion in 2100 is assumed). 5.5 Stabilization of greenhouse gas concentrations at any of the arbitrary levels explored above would be possible only if anthropogenic emissions were eventually reduced well below 1990 levels. It is possible to choose other stabilization levels and time scales and pathways for achieving them. 5.6 The global average annual per capita emissions of carbon dioxide due to the combustion of fossil fuels is at present about 1.1 tonnes (as carbon). In addition, about 0.2 (net) tonnes are emitted per capita from deforestation and land-use changes. The average annual fossil fuel per capita emissions in developed countries is about 2.8 tonnes and
Table 1 Without CH4 and N2O increase to 2050 With CH4 and N2O increase to 2050
450 560-760 450-620 1.1-3.3 varies from 1.5 to 5.5 tonnes. This compares to the figure of 0.5 tonnes for the same parameter in developing countries, ranging from 0.1 to 2.0 (in some cases more) tonnes. 5.7 Given cumulative emissions and population figures, global annual average per capita carbon emissions can be derived. As an illustration, for the median UN population projections, the future average annual per capita use of fossil fuel cannot much exceed the current global average if the atmospheric concentration of carbon dioxide is to remain below 550 ppmv. Annual average per capita emissions would be higher for stabilization levels above 750 ppmv, but still less than 2 tonnes.
Table 2 6. Technology and Policy Options Available to Approach the Objective of the Convention 6.1 An extensive array of technologies and policy measures capable of reducing greenhouse gas emissions is available. However, there are social, institutional, financial, market, and legislative barriers to their application and implementation. Hence their technical potential may not be fully realized. a. Energy Supply: Emissions from the supply sector can be substantially reduced by:
6.9 Several policy instruments are available to facilitate penetration of low carbon intensive technologies and the modification of consumption patterns. The optimum mix of instruments will vary from country to country and could include:
7.1 Article 2 provides the framework for cooperative decision-making in the international arena. 7.2 The uncertainties in the knowledge base make it difficult to assess the risks posed by anthropogenic climate change quantitatively. The inherent time lags between greenhouse gas emissions and climatic response and between climate change and ecosystems' adaptability (with potential irreversible impacts), and the lead times for infrastructure and capital turnover and for national and international political processes to come to fruition, need to be taken into account in making decisions. 7.3 Action to reduce greenhouse gas emissions could have other benefits such as reduced traffic congestion, air pollution and soil erosion. The market and no-market value of such secondary benefits depends upon local circumstances, but can be considerable. Action to reduce greenhouse gas emissions are likely to be more acceptable if designed to address simultaneously other concerns that impede sustainable development, and be more effective if tailored to local situations and developed through consultations with stakeholders. 7.3 Impacts and the costs of mitigation and adaptation will vary within and among countries raising issues of intranational, international and intergenerational equity. Perceived equity is an important element for legitimizing decisions and promoting national and international cooperation. 7.4 A sequential decision-making approach offers a prudent strategy that can be adjusted in the light of new information and could take into account factors such as future flexibility and current and future costs. Near term decisions along an optimal path (i.e., modest cost mitigation measures) will be the same for a wide range of ultimate stabilization concentrations.7.5 A broad portfolio of actions aimed at mitigation, adaptation and reducing uncertainties through further research provides a balanced approach to managing the risks of anthropogenic climate change. The appropriate portfolio will differ from country to country. A well- chosen portfolio of climate change investments will yield greater benefit for a given cost than any one option undertaken by itself. 7.6 Delaying action might reduce the overall costs of mitigation, but would increase both the adaptation and damage costs because of the rate and the eventual magnitude of climate change. 7.7 Stabilizing CO2 concentrations, for example, near or below even 750 ppmv would require immediate initiation of near term actions that include:
(i) research and development on energy efficiency improvements, alternative sources of energy and strategies to accelerate diffusion of new technologies into the market place; 7.11 "No regrets" measures are those whose benefits, such as reduced energy costs and lower emissions of local and regional pollutants, equal or exceed their cost to society, excluding the benefits of mitigation of climate change. Such "no regrets" mitigation and adaptation measures would appear justified on technical grounds unrelated to the risks of rapid climate change due to greenhouse gases. The expectation of net damages from climate change and the precautionary principle provide a rationale for going beyond "no regrets". Content Description: DRAFT: FOR INTERNAL USE ONLY DO NOT CITE/DISTRIBUTE THE IPCC ASSESSMENT OF KNOWLEDGE RELEVANT TO THE INTERPRETATION OF ARTICLE 2 OF THE UN FRAMEWORK CONVENTION ON CLIMATE CHANGE: A SYNTHESIS REPORT 1995 1.1 Since the last Ice Age, generations of human beings have adapted their settlements, agriculture, water use, responses to health hazards and commercial activities to current climate (temperature and rainfall) and soils. Nonetheless there are losses incurred yearly due to variability in climate and large losses incurred frequently as a result of extreme weather events such as floods, storms and droughts. Human-induced climate change would be a stress, in some cases a major stress, that would add to existing stresses such as population and the non-sustainable exploitation of natural resources. A large and/or rapid change in climate is likely to affect the distribution and availability of these resources. 1.2 Assessments of climate change in the last decade have consistently concluded that human activities are significantly changing the composition of the atmosphere so that a climate change will occur if greenhouse gases (GHGs) continue to be emitted at current or greater rates of emission. However, scientists are as yet not confident about how climate will change regionally nor about its impacts. 1.3 In recognition of these concerns, governments have negotiated, signed and ratified the UN Framework Convention on Climate Change (hereinafter called the Convention). The Convention has entered into force. Its objective is expressed in Article 2 (see box 1). Box 1 The ultimate objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner. 1.4 A determination of what concentrations of GHGs are "dangerous" inherently requires policy judgements. It is not the role of the IPCC to make such a determination. But the IPCC assessments can provide useful information on questions such as: the projected response of the climate system to different scenarios of future GHG emissions; the vulnerability of natural and socio-economic systems to changes in climate; potential outcomes under different timings and levels of stabilization of GHG concentrations; and technological and economic policy options available to reduce future GHG emissions and their effectiveness and associated costs and their distributions. The report is based on the contributions of the three IPCC Working Groups to the IPCC Second Assessment Report. 1.5 The elements and their interactions within and between the global climate system and the global socio-economic system are shown in figure 1. The upper part details the interactions in the climate system and the lower part focuses on the human system. FIGURE 1 Increasing Greenhouse Gas Concentrations, Radiative Forcing and Changes in Climate and Sea Level 2.1 There is agreement that the atmospheric concentrations of GHGs have increased globally due to human activities (see table 1). As a result, the radiative balance between the Earth and the atmosphere has changed. This change can be expressed in terms of a radiative forcing of global climate (see figure 2). 2.2 Small particles in the atmosphere (aerosols) arising from sulphur emissions from industrial sources and from biomass burning also have an important effect on radiative forcing. In contrast to most GHGs whose atmospheric lifetimes can vary from years to centuries, the aerosols have very short lifetimes (a few days). The concentrations of aerosols are therefore determined by current emissions. 2.3 Substantial uncertainty surrounds not only the future concentrations of aerosols (because the severe environmental problems of high sulphur emissions are causes of concern) but also the physical mechanisms governing their radiative forcing. Further, aerosols are very inhomogeneous in their geographical distribution. It is important therefore to distinguish between the effects of long-living greenhouse gases and those of aerosols. TABLE 1 Summary of key greenhouse gases affected by human activities
Gas
CO2 280 ppmv 355 ppmv 15ppmv/yr (0.4%/yr) 50-200* Almost entirely due to human activities * No single lifetime for CO2 can be defined because of different rates of uptake by different sink processes. ** This has been defined as an adjustment time which takes into account the indirect effect of CH4 on its own lifetime. (FIGURE 2) 2.3 Changes in global mean surface temperature and sea level are simple indicators of changes in mean climate. Global mean surface temperature (land and ocean) has increased by between 0.3 C and 0.6 C since the late 19th century and by 0.2 C to 0.3 c over the last 40 years, the period with the most reliable data (figure 3). Urbanization and land degradation account for only about 0.05 C of this increase. The warming has not been globally uniform: summer temperatures In the Northern Hemisphere in recent decades have been the warmest since about 1200 A.D; in some small regions (e.g., Northwestern North Atlantic), cooling has been observed. Over much of the land mass, the warming is associated with warmer nights rather than warmer days, although warmer days are also occurring. Figure 3 shows observed variability of surface temperature on interannual and decadal time scales which is similar to model estimates even when radiative forcing is absent. This variability arises from interactions between different components of the climate system and serves to mask trends due to systematic changes in radiative forcing. (FIGURE 3) 2.4 It is more difficult to determine whether global mean precipitation has changed. Increases are evident in some places but not in others. 2.5 Increasing surface temperature melts ice on land and warms the oceans. Thermal expansion of ocean waters and the water flowing from melting ice on land raises the level of the sea. (Melting sea ice does not raise the sea level.) Global mean sea level has risen by between 10 to 25 cm over the past 100 years. About half of this rise could be due to melting glaciers and sea water expansion. The remainder could come from melting of large ice sheets but this is not conclusive. 2.6 There have been both increases and decreases in extremes and variability of weather events during the last several decades. These changes have often been associated with the El Ni¥o - Southern Oscillation (ENSO) phenomenon. However, data are inadequate at present to determine whether there have been world-wide changes in variability and extremes. 2.7 An important question is whether the rise in the global mean temperature over the past century can be explained as natural variability or whether there is an identifiable contribution from human activities. Compared to the warming projected by models (see paragraph 3.1 also) which take account of the increase of greenhouse gases alone, the observed warming is smaller. But if the effects of aerosols are included in the models, projections agree better with observations. Comparisons of the patterns of the observed warming with model projections have also been performed. These comparisons find much unexplained variation, but agreement is generally better with model patterns that include both aerosols and greenhouse gases than those which include greenhouse gases alone. 2.8 Overall, the best evidence to-date suggests that global mean temperature changes over the last century are unlikely to be entirely due to natural causes, and that a pattern of climatic response to human activities is identifiable in the climatological record. 3.1 Scenarios of future anthropogenic emissions of greenhouse gases (and their precursors) and the precursors of aerosols are used as inputs for models that project future climates. Starting from emissions, it is possible to calculate future atmospheric concentrations on the basis of atmospheric chemistry and global carbon cycle models. Radiative forcing, which is the fundamental variable used by climate models, is linked to greenhouse gas concentrations through well-established physical relationships. Radiative forcing due to aerosols can also be calculated, but with greater uncertainty than for greenhouse gases. Projected Future Emissions of Greenhouse Gases and Aerosols (Emission scenarios) 3.2 In the absence of policies specifically designed to reduce anthropogenic GHG emissions, their atmospheric concentrations will increase. The key factors that determine future GHG emissions include population increase, energy demand, difficulties in moving away from fossil fuels giving rise to continuing heavy dependence on them, pressure on forests , increased use of private vehicles, etc. These various factors are assumed inputs in deriving plausible scenarios of future GHG emissions and contain uncertainties due to differing views on their future values and changes. Emission scenarios, which are not predictions, are divided into those which set out their projections in the absence of mitigation measures and those which take into account mitigation and adaptation measures. 3.3 The results of emission scenarios can vary considerably from actual outcomes even over short time horizons because the confidence in the applicability of their underlying assumptions diminishes as the time horizon increases. Therefore, an informed assessment of the possible consequences of uncertain future emissions paths necessitates the use of a range of scenarios. 3.4 A set of six emissions scenarios, the so-called IS92 scenarios a through f, are presented in the IPCC 1992 Supplement to illustrate a range of plausible future emissions. The scenarios assume no new policies to reduce greenhouse gas emissions (and are thus non-intervention scenarios as far as climate change is concerned). They extend to the year 2100 and include emissions of CO2, CH4, N2O, the halocarbons (CFCs and their substitutes HCFCs and HFCs) and sulphur emissions from industry and biomass burning. 3.5 The scenario of highest emissions (IS 92e) assumes high economic growth, moderate population growth, high fossil fuel availability and a phase- out of nuclear power. The IS 92a scenario provides a central case (not necessarily the most likely case) projection of global emissions. Use of coal is assumed to increase with time and renewable energy sources are assumed to replace fossil fuels only to a modest degree. Its world population projection is close to the medium projections of three international organizations and global economic growth assumptions are close to the average of other published scenarios. The IS 92c and IS 92d scenarios assume constraints on economic growth and fossil fuel use and low population projection of 6.4 billion in 2100 (for reference, current world population is 5.8 billion) and hence have low emissions. A summary of the assumptions in the scenarios is given in table 2. TABLE 2 3.6 Most published emission scenarios (including the IS 92 scenarios) show an increase in global annual greenhouse gas emissions, particularly CO2, over the next century. Virtually the only exceptions are scenarios which either incorporate very low population projections or policy measures. 3.7 To understand the potential impact of climate change policies on emissions and resulting concentrations of greenhouse gases, it is illustrative to consider emission scenarios that explicitly include different policy options. These options may contain measures specifically directed at climate change mitigation or measures which have much the same effect although differently motivated (e.g. intended to mitigate local and regional air pollution). The World Energy Council (WEC) developed emissions cases based on a medium population projection (11.3 billion by 2100), economic growth assumptions with faster (5.6% p.a) and slower (4.6% p.a.) possibilities for developing countries, adjustments of the official GDP for purchasing power parity rather than market exchange rates, alternative assumptions about the pace of future energy efficiency improvements and alternative fuel mix possibilities in the light of known reserves. 3.8 Two of the WEC scenarios imply atmospheric CO2 concentrations below 600 ppmv by 2100 (one around 450 ppmv), and even their high growth case implies concentration below 700 ppmv. These and other studies illustrate the scope for policy measures - not necessarily solely based on climate change mitigation - directed at raising energy efficiency, accelerating the diffusion of non-fossil forms of energy, and reducing local and regional expected damages, so far as feasible, arising from conversion and use of fossil fuels. 3.9 In figures 5 (a) and 5 (b) are shown the concentrations of CO2 and CH4 in the IS 92 emission scenarios. It is evident that these non-intervention scenarios lead to rising concentrations of the greenhouse gases. FIGURE 5 (a) FIGURE 5 (b) 3.7 Atmospheric concentrations of key long-lived greenhouse gases (such as CO2) at a given time are determined, to a first approximation, by the cumulative emissions up to that time. Cumulative emissions have a smaller range than annual emissions. Cumulative CO2 emissions for the years 1990 to 2100 in the IS92 scenarios range between 700 and 2080 GtC and between 230 and 330 GtC for 1990 - 2025. For comparison, emissions due to fossil fuel use between 1860 and 1994 amounted to 240 GtC (215 GtC for 1860 - 1990) and due to deforestation and changing land use to 80 - 120 GtC. On comparable (medium) population projections, the WEC cases indicate a range of 2.5 to 6 times past CO2 emissions (see figure 6). FIGURE 6 3.11 The emissions of sulphur dioxide, which are transformed into sulphate aerosols, depend primarily upon the sulphur content of oil and coal burned. The IS92 emissions scenarios assume that the anthropogenic sulphur emissions in 1990 amounted to about 80 TgS or million tonnes (for comparison, about 25 TgS were emitted from natural sources). This was projected to increase to 85, 115 and 130 TgS/yr respectively for the IS 92c, IS 92a and IS 92e scenarios in 2050 and to 60, 140 and 200 TgS/yr in 2100. These estimates are quite uncertain, but are the only ones available for use in projecting the future radiative forcing of anthropogenic aerosols.
Projected Changes in 3.12 Future changes of climate due to human activities are estimated by first deriving patterns of radiative forcing from scenarios of atmospheric concentrations of greenhouse gases and aerosols. The detailed response to these patterns of radiative forcing is obtained from models of the climate which take into account the physical and dynamical processes in all components of the climate system (atmosphere, ocean, land, ice and biosphere) and the interactions (most of which are non-linear) between them. Key to these model descriptions are feedbacks which act either to amplify or to reduce the basic radiative forcing signal. Because of our limited knowledge of these feedbacks, especially those involving clouds, considerable uncertainty remains in estimates of future climate change. Further uncertainty is associated with the role of the ocean which, because of its large heat capacity, acts to slow down the climate response to radiative forcing; the ocean also, through its ability to redistribute heat within the climate system, has an important role in determining the spatial patterns of climate change. 3.13 Many model estimates of climate change have been made for the particular case of an equilibrium atmospheric state in which the radiative forcing is increased to that which would occur if the CO2 concentration were doubled over its pre-industrial value (such an estimate is known as the climate sensitivity). The IPCC assessments in 1990, 1992 and 1995 reported that the global average temperature rise for doubled CO2 at equilibrium is most likely to be in the range of 1.5 C - 4.5 C with a best estimate of 2.5 C. 3.14 Estimates of global mean temperature change for all of the IS92 scenarios are shown in figure 7. The extreme and middle estimates reflecting the range (and hence the uncertainty) in the climate sensitivity are shown in figure 8.
FIGURE 7 3.15 For the central scenario (IS92a), global mean surface temperature increasesat a rate between 0.l6 C and 0.36 C per decade with greenhouse gases alone. If the effects of aerosols (less certain) are taken into account, the projected rates of warming over the next century are expected to be in the range 0.14 C - 0.28 C per decade. FIGURE 9 3.16 For the same scenario, global mean sea level would rise by between 0.3 and 1.0 m by the year 2100, if the greenhouse gases alone are considered. Inclusion of aerosols leads to a calculated rise over the same period of 0.2 to 0.8 m. (These values are for the IS92a scenario.) Sea level is expected to continue to rise for several centuries after stabilization of GHG levels. Projected Regional Changes of Climate and Sea Level 3.17 Models with and without aerosols indicate that a change of climate will not be distributed uniformly around the globe (figure 10). The confidence in their projections of regional climate change, however, remains low. This is partly due to approximations in current models, and to the fact that the inherent predictability of climate diminishes as geographical scale is reduced. FIGURE 10 3.18 Changes in future sea level will not occur uniformly around the globe. Recent model experiments suggest that the regional responses could differ by a factor of 2 to 3 from the mean due to regional differences in heating and changes in ocean circulation. In addition, geological and geophysical processes cause vertical land movements and these affect relative sea level changes on local and regional scales. 3.19 The following general conclusions, nevertheless, can be drawn relating to climate change due to increasing GHGs only: Warming is projected to be in general greater over land than over the oceans; Over land, maximum warming is expected in high northern latitudes in winter; Several model experiments indicate that south Asian monsoon will strengthen. 3.20 Since impacts are particularly related to climate variability and the occurrence of extreme weather events, possible changes in these deserve special attention. Model results lead to the following findings: A general warming tends to lead to an increase in high temperature events (heat waves) and a decrease in winter days below freezing; Models indicate that global average precipitation would increase in a warmer climate. The probability of heavy precipitation events leading to floods is expected to increase; All model experiments show that warming leads to increased evaporation. In regions that are currently prone to drought, droughts may become longer lasting and more severe; Models indicate changes in the precipitation patterns. In some places, increases in the probability of dry days and the length of dry spells (consecutive days without precipitation) are indicated. In those regions where mean precipitation decreases, droughts may increase markedly; Model experiments do not agree on systematic changes in overall storminess globally in a warmer world, but the possibility of systematic changes on the regional scale cannot be excluded; Changes of tropical cyclone frequency may be small in comparison with observed natural variability. There may, however, be some potential for changes of cyclone intensity in regions where sea surface temperature lies between 26 C and 29 C. 3.22 Questions are often asked regarding the long-term stability of climate and whether large, almost discontinuous, changes could occur as a result of increasing greenhouse gases. One such change is concerned with the circulation of the ocean on the largest spatial scale. For instance, it is this circulation which maintains the region of the North Atlantic ocean several degrees warmer than it would otherwise be. Several experiments with complex climate models indicate that this large scale circulation might weaken with global warming. Observations also show that some change in this direction might have occurred in the last few decades. Further, both the study of palaeo- climatic records and climate model experiments show that transitions to quite different circulation patterns might occur relatively rapidly. How likely is the occurrence of such events in response to global warming, how strong the radiative forcing will have to be for the change to be significant and the details of the accompanying changes are currently subjects of much scientific debate. 3.23 There is a very remote possibility that the West Antarctic Ice Sheet might gradually disintegrate because of a warmer climate, causing a significant rise in sea level. The specific circumstances under which such an event may occur are not known. 4.1 Human-induced climate change would represent an important stress in a world where many systems are already threatened by increasing resource demands and non-sustainable management practices. Both the magnitude and the rate of climate change are important in determining the inherent sensitivity and adaptability of ecological and socio-economic system (Box 2). This section assesses the sensitivity, and the potential for adaptation, of human health and selected ecological and socio- economic sectors to changes in climate. 4.2 Quantitative projections of the impacts of the magnitudes and the rates of climate change on any particular ecological or socio-economic system are difficult because (i) regional scale climate change predictions are uncertain, (ii) our understanding of many critical processes is limited, and (iii) the systems are influenced by multiple environmental and non- environmental factors. Moreover, most impact studies have only assessed how systems would respond to a climate change resulting from a (arbitrary) doubling of atmospheric carbon dioxide concentrations over its pre-industrial level. Very few have considered the evolving responses of systems to steadily increasing greenhouse gas concentrations over the corresponding period, and fewer still have examined the consequences of increases in greenhouse gas concentrations beyond doubling. Human Health 4.3 Projected changes in climate are likely to result in a wide range of human health impacts, most of them adverse, and many of which would reduce life expectancy. In many cases there is likely a threshold of minimum temperature associated with the occurrence of an adverse health impact. However, quantifying the impacts is difficult and depends on co- existent and interacting factors other than climate change, which include environmental circumstances and socio-economic conditions such as nutritional and immune status, water purity, population density, social infrastructure, working conditions and access to health care. Box 2 Sensitivity is the response of a system to a change in climatic conditions. Adaptation refers to adjustments in practices, processes, and structures of systems to projected or actual changes in attributes of climate. Adaptations can be autonomous or planned (planning could be reactive or anticipatory). The ability to adapt determines whether a system can turn new climate conditions into an opportunity to become more successful, or whether it incurs losses that weaken its efficiency or even its ability to survive. Most societies and resource-use sectors already contend with contemporary climatic variability and the wide range of associated natural hazards and unexpected opportunities. The ability of some systems to adapt to changes may be reduced by simultaneous exposure to other stresses (habitat fragmentation, acid deposition, influx of toxic pollutants, etc.). Some societies have more human, technological, and financial resources at their disposal with which to modify their environmental or social/economic systems. Vulnerability is the extent to which a system may be damaged or harmed by climate change and depends not only on the sensitivity of systems to variations in attributes of climate, but also on the ability of these systems to adapt by adjusting to new climatic conditions. Natural ecosystems are more vulnerable to climate change than managed ecosystems because adaptation options for the former are more limited and human intervention can control to some extent needed inputs of water and nutrients for the latter. Developing countries are more vulnerable to climate change than developed countries which have greater resources for adaptation. 4.4 Climate change can directly affect human health by increased exposure to very hot weather events and more frequent weather hazards (e.g., droughts, floods, and severe storms) increasing injuries, death, and destruction of public health infrastructure. An increase in the frequency and/or severity of heat waves would affect even populations that are acclimatized to high background temperatures resulting in several thousand additional deaths per year world- wide. Temperature increases in colder regions should result in fewer cold- related deaths. The ability to withstand severe heat waves depends upon the susceptibility of a given population, which is a function of socio-economic differences, physiological acclimatization, and cultural-technical adaptation. Temperature and humidity thresholds and physiological tolerances vary and generally increase towards the equator. 4.5 Climate change can indirectly affect human health through altered disease transmission and nutritional status and exacerbation of existing health disorders. Increases in transmission of vector-borne infectious diseases may result from increases in the geographical distribution of the vector organisms of those diseases (e.g., mosquitoes that spread malaria, dengue and yellow fever; water snails that spread schistosomiasis; and black flies that spread river blindness), and from climate-change driven variations in the life-cycle dynamics of both the vector and the infectious parasite. With malaria for example, the parasite cannot develop inside its mosquito host at temperatures below 16 C. There is already evidence that malaria, yellow fever and dengue fever are persisting at higher altitudes and latitudes. It is estimated that the potential transmission of malaria and river blindness could increase by approximately 20% (i.e., an extra 50- 80 million prevalent cases of malaria and 3.5 million cases of river blindness). Any such increase would primarily affect tropical, subtropical, and some less well-protected temperate-zone populations currently at the margins of endemically infected areas. Increasing transmission of certain contagious diseases (cholera, for example, through an increase in algal blooms in warm coastal waters and wetlands) may also be caused by changes in climate. Climate-change related decreases in food production may impair nutritional status, especially in some developing countries whose populations currently have insecure access to food supplies. Conversely, climate change may also help improve food production, and therefore nutritional status, in some regions. Finally, climate change may exacerbate respiratory disorders and allergies by intensifying the effects of air pollution (ozone and particulates), particularly in densely-populated urban areas. 4.6 Options for adapting to the potential health effects of climate change are available. However, much of the world's population already suffers from poor environmental health conditions and has little access to health care, and these populations would be the least likely to have access to adaptive measures. At the population level, public health surveillance- and-control measures (especially for infectious diseases), the introduction of protective technologies (e.g. insulated buildings, air- conditioning), improved primary health care (such as use of malarial prophylactics and vaccines such as that for yellow fever), and improved large-scale health monitoring could play a significant role in reducing the range of health impacts. At the individual level, people can be encouraged to limit dangerous exposures (e.g. by use of protective clothing, mosquito nets, repellents, sun screens, etc.). Water Systems 4.7 Fresh water, an essential component of national welfare and productivity, is an increasingly scarce commodity. The world's agriculture, hydroelectric and thermal power generation, municipal and industrial water needs, water pollution control, and inland navigation depend on the natural endowment of surface and groundwater resources. Reductions in natural freshwater resources could result in chronic shortages in regions that are already under stress and for which there is considerable competition among users. 4.8 Climate change could represent an additional stress on the hydrological cycle that is already under a variety of stresses, such as depletion of aquifers, urbanization, changes in vegetative cover, and chemical contamination. The complexity of the hydrological system and the many influences on it, combined with the uncertainty of the regional distribution of changes in temperature and precipitation in climate model results, make it difficult to project precisely where stresses on water resources would be greatest. 4.9 Current evidence suggests that a warmer climate would result in changes in the timing, regional patterns, and intensity of precipitation events. This would lead to changes in the seasonal availability of water for agriculture and supplies of drinking water (timing of precipitation); river flow (regional patterns of precipitation); and flooding (intensity of precipitation). While climate models project increases in global mean precipitation, higher temperatures would increase evapotranspiration. Higher evaporation rates may lead to reduced run- off and streamflow in some areas despite increased precipitation. 4.10 Global climate change would have the largest effects on countries which extract a high percentage of their available water resources. In particular, the current arid and semi-arid regions of the world are likely to be significantly affected and could experience the largest decreases in run-off, the latter posing the greatest challenges for water resources management. 4.11 Management of water resources should be a continuously adaptive enterprise, responding to changing demands, hydrological conditions, technologies, and economic shifts. Water management practices seek to control demand for water, and to increase supplies, for example, by increasing reservoir capacity. However, experts disagree over whether water supply systems will evolve substantially enough in the future to compensate for the anticipated negative impacts of climate change on water resources and for potential increases in demand. To the extent that existing water supply and quality problems are not addressed, especially in developing countries, optimistic projections about adequate water supplies of sufficient quality will not hold. Natural Ecological Systems 4.12 Ecosystems are regulated by numerous aspects of the physical environment such as atmospheric composition, soil properties, topography, and climate variables such as temperature, precipitation, and cloudiness. Changes in climate, and associated changes in the frequency of fires and prevalence of pests could alter the structure (biological diversity) and function (productivity, carbon storage and nutrient recycling) of terrestrial ecosystems, thus affecting the critical goods and services they provide to society. These goods and services include: (i) provision of food, fibre, medicines, and energy; (ii) regulation of water run-off to control floods and soil erosion; (iii) assimilation of wastes and purification of water; and (iv) maintenance of an attractive environment for recreation and tourism. While population increases and human decisions about land use and harvesting intensities will probably represent the greatest pressures on most terrestrial and marine ecosystems for the foreseeable future, climate change would represent a significant additional stress factor. Forests 4.13 The consequences of climate change for forest ecosystems depend on the magnitude and the rate of change and their potential to adapt. The rate at which climate zones shift is important because different species migrate at different rates, depending on their growth and reproductive cycles. A global mean warming of 1 C-4 C over the next 100 years would be equivalent to a poleward shift of temperature bands of approximately 160-640 km. The historical migration rates for tree species, based on the palaeo-environmental record, are generally believed to be on the order of 4 - 200 km per century. Thus some forest species may be unable to migrate sufficiently rapidly to keep pace with shifts in the climate zones. 4.14 An increase in mean annual air temperature of 1 C is sufficient to cause changes in the growth and regeneration capacity of many forest species, and hence in the composition of forest ecosystems. Under a doubled-CO2 equilibrium climate scenario, global models project major changes in vegetation types, (i.e., transformation from one equilibrium vegetation class to another) over a substantial fraction (14- 65% with a global mean of 34%) of the existing forested area of the world. Boreal forests will be most affected, with tropical forests being least affected. Such a transition will have implications for animal and microbial biodiversity because of habitat loss, as well as for commodity extraction and management practices within forests. 4.15 While it can be inferred that higher rates and larger magnitudes of change will have stronger impact, a key uncertainty is the fate of forested systems during the transition from one equilibrium climate to another (assuming a new equilibrium will be established). Changes in species range, disturbance regimes (fires, pests, and diseases), and increased temperatures (which increases respiration) may decrease standing biomass during the transition, even though the net primary productivity of forests may increase due to the so- called CO2 fertilization effect (see paragraph 4.24 also). 4.16 Measures to assist adaptation in unmanaged ecosystems are not well developed, especially for complex forested ecosystems. Human activities fragment most landscapes limiting the ability of populations to follow changing habitat distribution. One adaptation strategy would be to establish a distributed system of reserves based on model projections of future habitats. Migration to such reserves (or other appropriate habitats) could be assisted by transplantation or by means of migration corridors of relatively undisturbed habitat and by reducing the competition for resources or other stresses at critical stages in life-cycles (e.g. seedling stage for plants, juvenile period for animals). 4.17 Article 2 provides that GHG concentrations be stabilized in a time- frame sufficient to allow ecosystems to adapt naturally to climate change. Ecosystems do not adapt to climate change but individual species do. Hence, the rate of climate change affects the way in which ecosystems disassemble-assemble and reassemble into new ecological systems. At the present rate of GHG emissions, global mean temperatures are projected to increase by about 0.2 C per decade, a rate which is at least twice the historically observed maximum rate. Therefore, forested ecosystems will be unable to completely adjust to such rates and some species may become extinct. Coastal Ecosystems 4.18 Coastal ecosystems such as salt-water marshes, mangrove ecosystems, coastal wetlands, coral reefs, coral atolls and reef islands provide a wide range of goods and services to society such as providing important habitats and nurseries for wildlife and fish and centres for tourism and fishing, and protecting islands and coastal areas from wave actions and severe storms. These ecosystems are under various stresses including overexploitation of resources, pollution, sediment starvation and urbanization. They are also exceptionally vulnerable to increases in temperature and sea level. 4.19 Coral reefs, coral atolls and reef islands and deltas are particularly vulnerable to even modest increases in temperature, resulting in a significant increase in the frequency of coral bleaching, submergence, and coastal erosion. If seawater temperature increases of 3 C-4 C are sustained for a period of months, considerable coral mortality can ensue. Severe bleached corals can take decades to centuries to recover. 4.20 Sea level is projected to increase at a rate of 2-8 cm per decade (20-80 cms by 2100) for the IS92 emission scenarios, a rate several times faster than experienced during the last 100 years. Reef accretion rates are typically 1- 10 cm per decade and hence corals should not be particularly vulnerable to increases in sea level unless accretion rates significantly decrease due to warmer sea temperatures.
Vulnerability of Socio-Economic Sectors 4.21 Based on several model projections of future global food production, one view holds that global food availability would increase relative to population. An alternative view is that the historical trend of generally improving food supply will not be continued because of resource degradation and the inability of technological advances to keep up with population growth. Climate change would represent yet another stress on some of the world's agroecosystems. 4.22 Agricultural productivity is sensitive to two broad classes of climate- induced effects on the quality and quantity of harvestable yield: direct effects from changes intemperature, water balance, atmospheric composition and extreme weather events; and indirect effects through changes in soils and the distribution and frequency of infestation by insects, diseases, weeds, and other predators. The vulnerability of agricultural production to climate change depends not only on the physiological response of the affected plants, but also on the ability of the affected socio-economic systems of production to cope with fluctuations in yield. 4.23 Recent studies have confirmed the conclusion of the IPCC 1990 Assessment that the aggregate effects of climate change on global agricultural production are likely to be small to moderate. However, global food supply is only one aspect of the issue and large differences are projected at local and regional scales. Studies tend to show more negative impacts for areas in the tropics where many of the world's poorest people live and where individuals are currently at greatest risk of hunger. Large yield losses in one locality and for one type of crop are balanced by large gains in other localities, both within and among countries (e.g. frequently more than +/- 20 %). Low- latitude, low- income populations depending on isolated, dryland agricultural systems in semi-arid and arid regions are particularly vulnerable. Many of these populations at risk are in Sub- Saharan Africa, South, East and South East Asia, as well as some islands in the Pacific. The risks may be underestimated because the studies do not include indirect effects of climate change on agriculture via insects, weeds and diseases. 4.24 Several major food crops (e.g., wheat, rice, and soybeans), should benefit from improved water use efficiency and increased productivity because of the interaction of increased atmospheric concentrations of carbon dioxide and their particular photosynthetic process (the so-called CO2 fertilization effect). On average, such crops will see a 30 percent increase in yield (for a doubled carbon dioxide environment), although the variation in response is wide (-10 to +80 percent). Temperature increases at high latitudes are likely to increase crop growth, through lengthening and intensifying of the growing season, assuming adequate availability of water and suitable soils. At low and low-to- mid latitudes, where temperatures are already high, temperature increases may cause increases in the frequency of heat stress on crops and decreases in available water through higher rates of evaporation and transpiration. In contrast, some other major crops (e.g., sugar cane, maize, millet, and sorghum) and some common weeds, which have different photosynthetic processes, will benefit less from increased carbon dioxide concentrations. 4.25 Adaptation will be important to limit losses or take advantage of changing climatic conditions. Major classes of agricultural adaptation options considered in the literature include: (i) breeding new crops and cultivars for changed climate conditions; (ii) improved management strategies such as altered irrigation practices or planting times; (iii) adding nutrients to take full advantage of the projected CO2 fertilization effect; (iv) employing soil conservation and protection strategies; and (v) research on pest control. The incremental costs of adaptation could be a serious burden for developing countries. Coastal Zones and Small Islands Infrastructure 4.26 Sea-level rise can have a number of negative impacts on tourism, ports and harbours, human settlements, natural freshwater systems in coastal areas, agriculture, insurance industry, and cultural systems and values. Climate change projected for the IS 92 emission scenarios would increase the vulnerability of coastal populations to flooding. Currently an annual average of about 50 million people experience flooding due to storm surges. A 50 cm sea- level rise would increase this number to about 92 million and a 1 meter sea- level to about 118 million. The estimates will be substantially higher if one incorporates population growth projections. Developing country populations, such as those of Bangladesh or China, will be more vulnerable because their existing sea and coastal protection systems are less well established and also because their population growth rates are higher, putting more people at risk. For such countries, sea-level rise could force internal or international migration of populations. 4.27 A number of studies have evaluated the sensitivity to a 1 meter sea level rise (the upper end of the range projected for the IS 92 scenarios). These studies show that small islands and deltaic areas are particularly vulnerable with land losses, for example, of 0.05% in Uruguay, 1.0% in Egypt, 6% in the Netherlands, 17.5% in Bangladash and about 80% in the Marshall Islands. In some cases, such land losses can be reduced through coastal protection measures. However, there are major technical, environmental and economic constraints in implementing them. While annual adaptation/protection costs for these nations are relatively modest (about 0.1% GDP), average annual costs to many small island states and deltaic coasts are much higher amounting to several percent of GDP assuming that adaptation is at all possible. Many nations face loss of capital value in excess of 10% of GDP. Large numbers of people would be affected, e.g., about 70 million in both China and Bangladesh. 4.28 For coastal states with access to financial and technical resources, a wide array of management options are available to prevent, ameliorate or compensate for coastal-zone damages encountered under current climate variability and which could be encountered under future climate change. The emphasis in the past has been on engineering responses to coastal erosion and protection against flooding, with action often being triggered in response to an extreme event. Heavily populated industrial and urban areas are primary candidates for structural protection measures such as dikes, seawalls and breakwaters. These are high-cost options. Economic evaluation principles, especially risk assessments and cost-benefit analyses, should be of use in deciding whether to protect or retreat. In addition, the range of options includes non- structural adaptation such as zoning, land-use regulation and flood-damage insurance, with emphasis on a precautionary approach in locating investments. Conclusions on Vulnerability to Climate Change 4.29 There are a number of important conclusions that are not specific to any one ecological or socio-economic system:
For natural ecosystems ,this would result in: Human health and habitats are also at risk. For human health, a critical issue is possible increase in the incidence of vector-borne diseases such as malaria, especially in developing countries, and heat spells. Some parts of human habitats are likely to be destroyed by sea level rise and possible change in extreme weather events, causing migration of populations and placing additional stresses on already stressed social and political systems. TABLE 3 System Consequence Adaptation Potential Natural Ecosystems: Forests Montane Coastal marshes Coral reefs Loss of species and goods and services - ditto - - ditto - - ditto - Limited but costly Non-existent Very limited but costly Non-existent Cryosphere Loss of glaciers, reduced snowpack Non-existent Agriculture Redistribution, reduced yields in developing countries High but potentially costly Water resources Reduction in quantity and quality High but costly Human settlements Coastal and river flooding threatening human habitat, causing displacement of people High but costly Human health Loss of life, increased diseases High but costly 4.31 The economics literature contains a few aggregate estimates of the damages associated with a doubled CO2 concentration scenario. The estimates suggest that the associated warming would impose net damages equivalent to between 1.5% and 2.0% of world GDP on the present world economy. The regional variation in climate change damage would be substantial. However, there is little agreement across the studies about the magnitude of each category of damages or the relative ranking of the damage categories. Climate changes of this magnitude are not expected to occur for some decades and damages in the interim would be smaller. Some impacts, such as potential loss of low- lying areas, may be so significant physically and culturally that no monetary compensation would be sufficient. [NOTE: This paragraph will be made consistent with the 1995 Summary for policymakers of Working Group III.] Box 3 The Framework Convention on Climate Change defines its objective (in Article 2) as stabilization of greenhouse gas concentrations in the atmosphere. Stabilization of emissions is often confused with stabilization of concentrations. Stabilization of emissions refers to a situation in which the GHG emissions in one year are the same as in the previous year. A stable concentration of a greenhouse gas refers to a state of dynamic equilibrium between the atmosphere, the ocean, and the terrestrial ecosystems. In this state of equilibrium, aggregate annual emissions of the gas from the surface of the planet are just balanced by removals of the same gas from the atmosphere. As a consequence, the concentration of the gas in the atmosphere remains unchanged. 5.1 As noted in the previous sections, some damage and adaptation costs of a human-induced climate change may be unavoidable. Even though there are major uncertainties about the magnitude and pace of a climate change due GHG emissions and about how serious it will be, the uncertainties do not diminish the risk itself but merely make its quantification difficult. Risks would vary markedly from country to country. 5.2 An analytical approach to the issue of stabilization of concentrations is presented in the following pages. It is purely illustrative and designed to expose the dimensions of the problem only. It has no implication of policy recommendation whatsoever. 5.3 The Convention in Article 3 (see box 4) provides that the type of strategy to be used in reaching its objective should be comprehensive, covering all relevant sources, sinks, and reservoirs of greenhouse gases. It is important to keep this provision in mind when synthesizing scientific- technical information relevant to Article 2. Because of the multiplicity of sources and the variety of gases involved, there is no single strategy for stabilization. Box 4 In their actions to achieve the objective of the Convention and to implement its provisions, the Parties shall be guided, inter alia, by the following: 1. The Parties should protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities. Accordingly, the developed country Parties should take the lead in combating climate change and the adverse effects thereof. 2. The specific needs and special circumstances of developing country Parties, especially those that are particularly vulnerable to the adverse effects of climate change, and of those Parties, especially developing country Parties, that would have to bear a disproportionate or abnormal burden under the Convention, should be given full consideration. 3. The Parties should take precautionary measures to anticipate, prevent or minimize the causes of climate change and mitigate its adverse effects. Where there are threats of serious or irreversible damage, lack of full scientific certainty should not be used as a reason for postponing such measures, taking into account that policies and measures to deal with climate change should be cost-effective so as to ensure global benefits at the lowest possible cost. To achieve this, such policies and measures should take into account different socio- economic contexts, be comprehensive, cover all relevant sources, sinks and reservoirs of greenhouse gases and adaptation, and comprise all economic sectors. Efforts to address climate change may be carried out cooperatively by interested Parties. 4. The Parties have a right to, and should, promote sustainable development. Policies and measures to protect the climate system against human-induced change should be appropriate for the specific conditions of each Party and should be integrated with national development programmes, taking into account that economic development is essential for adopting measures to address climate change. 5. The Parties should cooperate to promote a supportive and open international economic system that would lead to sustainable economic growth and development in all Parties, particularly developing country Parties, thus enabling them better to address the problems of climate change. Measures taken to combat climate change, including unilateral ones, should not constitute a means of arbitrary or unjustifiable discrimination or a disguised restriction on international trade. 5.4 The direct radiative forcing due to enhanced concentrations of all greenhouse gases in the atmosphere was about 2.4 W/m2 in 1994 of which 1.55 W/m2 was due to increased carbon dioxide (see figure 2). The forcing due to all greenhouse gases in 1994 was equivalent to that due to a concentration of CO2 alone of (about) 420 ppmv. Thus the figure of 420 ppmv CO2 is the equivalent CO2 concentration for the radiative forcing of 1994. (For comparison, the actual CO2 concentration in 1994 was 356 ppmv.) The concept of equivalent CO2 concentration is helpful in approaching the simultaneous stabilization of all the GHG concentrations in the atmosphere - the so-called comprehensive approach. 5.5 The individual reductions in emissions for stabilizing the concentrations of carbon dioxide, methane, nitrous oxide and halocarbons, and thereby implicitly stratospheric ozone, can be combined in different ways for stabilizing the total global radiative forcing in the comprehensive approach. To these, the forcing due to changes in tropospheric ozone and aerosols should be added; this cannot be easily done - and has not been done in the illustrations that follow - because of limited information on their future concentrations and geographical distributions. 5.6 Different greenhouse gases have different residence times in the atmosphere. Tropospheric ozone and tropospheric aerosols have residence times of the order of a day and of a week respectively. Their concentrations are governed directly by the emissions of their precursors. Methane has a residence time of 12-17 years and will stabilize in about 50 years if its emissions were stabilized. Other greenhouse gases have longer residence times spanning many decades to centuries. The concentration of each of them is governed by some (determinable) fraction of its emissions accumulating in the atmosphere over decades to centuries. The concept of cumulative emissions of the long-lived greenhouse gases helps in understanding the complexities associated with stabilization. Carbon Emissions and Stabilization of CO2 Concentrations 5.7 Because carbon dioxide presently contributes more than half of the direct annual increase in the radiative forcing (with probably a greater fraction in the future), stabilizing CO2 concentrations in the atmosphere would appear to be necessary for stabilizing future total global radiative forcing. 5.8 Profiles of atmospheric CO2 concentrations can be constructed assuming smooth variations in the rates of increase in its concentrations from the current value to different stabilization levels. Such profiles for concentrations of 350, 450, 550, 650 and 750 ppmv, published previously by the IPCC, are shown in figure 11. It is possible to choose other stabilization levels and time scales and pathways for achieving them. FIGURE 11 5.9 Carbon cycle models can be used to derive profiles of total anthropogenic carbon emissions corresponding to the concentration profiles shown in figure 11. Such emission profiles are shown in figure 12. More rapid increases in the concentrations in the beginning would lead to higher initial emissions than those given in figure 12, but greater reductions would be necessary later if stabilization were to be achieved at any given concentration. Emissions to achieve the stabilization levels illustrated here are, after some decades, lower than those of the IS 92 scenarios. Also, all emissions eventually have to be below the 1990 emissions and be maintained there. Emissions would be greater for stabilization levels higher than those shown in figure 11. FIGURE 12 5.10 Figure 13 provides, as an illustration, estimates of cumulative global carbon emissions until the year 2100 for various stabilization levels of CO2. The figure also illustrates cumulative emissions for the IS92a emissions scenario. (These values may be compared to the estimated emissions of 240 GtC from fossil fuel use between 1860 and 1994, about 60% of which came from burning solid fuels.) FIGURE 13 5.11 Because of the inertia of the carbon cycle and of the socio-economic system, it would take a decade or two for significant deviations from non- intervention emissions profiles to become noticeable. The selection of the illustrative concentration profiles (figure 11) assumes this inertia and consequently the emissions in figure 12 do not deviate much from each other in the first decade or two. A delay beyond a few years hence to initiate appropriate measures to reduce emissions would result in steeper rates of reduction later, if, for example, stabilization of CO2 is aimed for at 550 ppmv or below. 5.12 Given cumulative emissions and population figures, global annual average per capita carbon emissions can be derived. Figure 14 shows values of annual average per capita emissions derived for stabilization of CO2 concentrations at 450, 550, 650 and 750 ppmv, taking the corresponding cumulative emissions from figure 13 and assumingthe UN median estimates of population growth to about 9.5 billion in 2050 and about 11 billion persons in 2100. If other population estimates were used, the values would change accordingly. FIGURE 14 5.13 The average annual per capita carbon emission for the globe as a whole due to fossil fuel burning is at present about 1.1 tonnes. (In addition, a net of 0.2 tonne is emitted from deforestation and land-use change.) It is on average about 2.8 tonnes from fossil fuels in developed countries (including countries with economies in transition). National annual per capita emissions vary between 1.5 and 5.5 tonnes. In the developing world, the average annual per capita emission is about 0.5 tonne (with a range of 0.1 to about 2.0 tonnes). The future global average annual per capita emissions from fossil fuel use cannot exceed the current global average by very much if the atmospheric concentration of carbon dioxide is to remain at 550 ppmv (about double the pre-industrial level) or below. Larger annual per capita emissions would be possible if stabilization at higher concentrations were to be aimed for. Stabilization of Other Greenhouse Gases 5.14 Methane: The atmospheric residence time for methane, at 12 to 17 years, is comparatively short. If current emissions and removal rates were held constant, atmospheric concentration would stabilize at about 1.9 ppmv (compared to the 1994 concentration of 1.73 ppmv and the estimated pre- industrial concentration of about 0.65 ppmv). On the other hand, stabilization at present concentration would require a reduction in the emissions by about 10%. 5.15 Nitrous oxide: The lifetime of nitrous oxide in the atmosphere is about 120 years. A reduction of anthropogenic emissions by about 50% is required in order to stabilize the concentration at present level. If emissions were stabilized at the present level, the concentration would increase to about 400 ppbv during the next century (compared to 310 ppbv today and an estimated pre-industrial concentration of approximately 280 ppbv). 5.16 Halogen-containing compounds and stratospheric ozone: The concentrations of the CFC-gases in the atmosphere are expected to stabilize gradually in the next few years. A very slow decrease in their concentrations is then expected and a return towards natural stratospheric ozone concentrations during the 22nd century. 5.17 Other than CFCs, most other halocarbons have lifetimes in the atmosphere of years to a few decades. Their contributions to human- induced radiative forcing is slight at present. The lifetimes of HCFC-22 and HFC-134 are 13 and 18 years respectively. The projected increase in their emissions in the IS92a scenario implies that a decade or two into the next century, these gases would be contributing more than 0.1 W/m2 to the radiative forcing. 5.18 Some very long-lived greenhouse gases are also being emitted into the atmosphere, although still in very small amounts (e.g., sulphur hexafluoride or SF6 and perfluoromethane or CF4 with lifetimes of 3,200 and 50,000 years respectively). The long lifetimes of these gases make them very difficult to stabilize implying rising concentrations for centuries after steps to eliminate their emissions are put in place. 5.19 Concentrations of tropospheric ozone and of tropospheric aerosols respond quickly to changes in the emissions of the precursors, as has been mentioned earlier. The Concept of Equivalent CO2 Concentrations and the Comprehensive Approach 5.20 As an illustration, let us consider the stabilization of radiative forcing due to all greenhouse gases, i.e., the radiative forcing due to the equivalent carbon dioxide concentrations of, say, 450, 550, 650 and 750 ppmv. Other choices of concentrations can equally well be made. For each case, we ask what level of concentration is required for carbon dioxide alone for stabilization, if simultaneously demanding that methane and nitrous oxide are either (i) stabilized at present levels (hereinafter referred to as "N2O and CH4 stabilization now") or (ii) permitted to increase according to IS 92a scenario until 2050 and stabilize thereafter (hereinafter referred to as "N2O and CH4 stabilization in 2050"). It is possible, then, to deduce the approximate levels of stabilization for carbon dioxide required for stabilizing equivalent CO2 concentrations. These are illustrated in table 4. 5.22 It may be seen from the table that, for example, stabilization of equivalent carbon dioxide concentration at 450 ppmv would require a stabilization in CO2 concentration alone at about 385 and 365 ppmv, respectively, for N2O and CH4 stabilization now and in 2050. Stabilization of equivalent CO2 concentration at 550 ppmv (equal to almost a doubling of the pre-industrial CO2 concentration) would require a stabilization of CO2 alone at about 480 and 455 ppmv, respectively, for N2O and CH4 stabilization now and in 2050. TABLE 4 Stabilization level of equivalent CO2, ppmv 450 550 650 750 Enhanced radiative forcing, W/m2 3.2 4.4 5.4 6.2 Increase of global mean temp. at stabilization, C 1.1-3.3 1.5-4.5 1.8-5.6 2.1-6.3 Maximum CO2 concentration for "N2O and CH4 stabilization now" 385 480 565 650 Maximum CO2 concentration for "N2O and CH4 stabilization in 2050" 365 455 535 610 Uncertainties in the CO2 concentrations in the table are +/- 30 ppmv. 6.1 An extensive array of technologies and policy measures exist to mitigate anthropogenic greenhouse gas emissions in the energy, industrial, and agriculture sectors, and to enhance natural sinks through forestry and land management. The rate and degree of diffusion of the technologies will be influenced by fiscal and regulatory measures, additional research, and dissemination of information. The policy measures will be more effective if they are developed through consultations with various stakeholders and are carefully tailored to local situations. Energy Sector
6.2 The options for reducing energy-related emissions fall into two general categories: Energy Supply Options 6.3 Technologies exist with potential to reduce GHG emissions substantially over 50-100 years. They can be developed to provide energy services at projected costs comparable to the projected costs of conventional sources of energy. Much of the world's commercial energy system will be replaced at least twice by the year 2100. Such replacement times provide opportunities to change the energy systems in the course of normal investment cycles. 6.4 In the energy supply sector, GHG emissions reductions are possible through the following technology options, listed in no particular order of priority:
6.5 Development of alternative sources of energy can be coupled to efforts to reduce existing inefficiencies in energy end-use. The technical potential for efficiency improvements on the demand side is large. Numerous studies have indicated that 10-30 % efficiency gains are feasible with current plant and equipment in many parts of the world at little or no cost. Using plant and equipment which presently yields the highest output of energy service for a given input of energy, efficiency gains of 50-60 % would be feasible in developing countries if requisite technology and financing became available. 6.6 More than a third of global CO2 emissions come from the industrial sector through energy use and production processes. Other greenhouse gases are also emitted through production processes. Basic processes including production of iron and steel, chemicals, building materials and food account for more than half of all the energy used in this sector. Industry has made substantial reductions in energy intensity in the past two decades. Improvements in energy efficiency have, in some countries, permitted major increases in production with little or no increase in energy use. The potential in the relative short-term for efficiency improvements in the manufacturing sector in the leading industrial nations is around 25 percent. 6.7 Emissions reductions are feasible through other efficiency improvements (e.g., materials savings, co-generation and steam recovery, use of more efficient motors and electrical devices), recycling materials and switching to those with lower CO2 content, developing fundamentally new processes ("industrial metabolism" that uses less energy), lowering of materials intensity in manufacturing ("dematerialization"), and feasible reductions in the emissions of gases such as halocarbons, CH4 and N20 in industrial proceses such as production of iron, steel, aluminum, ammonia, etc. The emissions reductions and costs associated with specific technologies or approaches in each of these categories will vary, according to current patterns of industrial energy and materials use. Some countries, for example, use twice as much energy to produce a unit of steel as do other countries, thus affording opportunities to achieve significant emissions reductions. 6.8 About 25% of global primary energy use in 1990 and 22% of CO2 emissions from fossil fuel use came from the transportation sector. This is the most rapidly growing source of GHG emissions. Whereas transportation world-wide consumed 68 EJ (1 EJ = 1018 J) in 1990, mostly in oil products, this sector could account for 65-170 EJ by 2025 and 30-520 EJ by 2100 according to the IS 92 and WEC scenarios. About 75 percent of energy use and greenhouse gas emissions in this sector are now in industrialized countries; greater growth is expected in developing countries in the future. Vehicle ownership and use ranges from 1.7 people per car or light truck in the USA to about 600 people per car in China. The nature of production and demand for vehicles in OECD countries influences the pattern of demand for transportation services throughout the world. 6.9 Two key areas in this sector provide opportunities to reduce emissions significantly: Changing the design of all vehicle types to use more efficient drive trains, body shapes and materials, as well as switching fuels for propulsion. The potential for reduction in energy intensity through these measures in 2025, without losses in vehicle performance and size, is 35- 60% in cars, 20-40% in heavy trucks, and 30-50% in aircraft. If performance and size were changed, greater energy intensity reductions could be achieved. More than 95% reductions in GHG emissions relative to 1990 levels are feasible per unit of transport service, if a switch to alternative fuel and electric powered vehicles using renewable energy sources is coupled with the foregoing reductions in energy intensity. Altering land-use patterns, transport systems, mobility patterns and life styles to reduce the level of passenger miles travelled and freight transport activity, and shifting to less energy intensive transportation modes. 6.10 Actions to reduce greenhouse gas emissions from transport can simultaneously address other problems, including traffic congestion, high accident rates, noise and local air pollution including emissions of particulates, NOx and VOC that are precursors to tropospheric ozone. Much experience has already been gained in the effective use of policies such as fuel and vehicle taxes and fuel economy standards to encourage energy efficiency improvements. Research will continue to be needed to develop new propulsion systems and affordable, lightweight materials. 6.11 Human settlements currently account for about one-third of GHG emissions. The largest portion is in the form of CO2 emissions from energy use in buildings; most of the remainder is in the form of methane from solid waste and industrial/domestic waste water. While the range in current and projected energy use and emissions in this sector is large, the "best guess" estimate is 2% growth in energy use per year (assuming continuing economic growth and improvements in energy efficiency), leading to a doubling of energy use by 2030. 6.12 Some examples of technologies that could cut projected growth in emissions by one-half over the next 35 years (and more in the longer run) without diminishing energy services include more efficient space- conditioning systems, reduced heat losses through walls, ceilings and windows, more efficient lighting and more efficient appliances (refrigerators, water heaters, cook stoves, etc). Other technologies that can capture, reduce, or prevent methane emissions (e.g., in landfills) are also increasingly available.
6.13 Activities that provide the best opportunities for reductions in emissions growth in buildings are: Land Management 6.14 There are options for increasing carbon storage and/or for reducing emissions of carbon dioxide, methane and nitrous oxide in managed sectors such as agriculture and forestry. In general, mitigation options in these sectors focus on more sustainable uses of existing resources and have other positive effects such as reducing air and water pollution, slowing the rate of land degradation and conserving biodiversity. The mitigation potential in these options, however, appears insufficient to bring about reductions in emissions to stabilise greenhouse gas concentrations. 6.15 Estimates of the total amount of carbon that could be sequestered in the forestry and agriculture sectors over the next 50 years range from 90 to 150 GtC, which is equivalent to 8 to 40% of the projected cumulative fossil fuel emissions over the same period in the IS92 emission scenarios. Significant uncertainties are associated with estimating the amount of carbon that can thus be conserved and/or sequestered. They include the magnitude of the CO2 fertilisation effect, interactions between carbon- storage potential and changes in temperature, precipitation and the availability of other nutrients, changes in the frequency of disturbances such as fires and pest outbreaks, land availability for forestation and regeneration programmes, lack of information about current land-use practices and rates at which deforestation can be reduced. Carbon sequestration through improved management of forests and agricultural lands 6.16 The categories of promising forestry activities include: (i) management and conservation of existing carbon in forests as for example by slowing deforestation; (ii) expanding carbon storage by increasing the area and/or carbon density of native forests; and (iii) increasing the use of forest biomass in products such as bio-fuels and long-lived wood products which can substitute for fossil-fuel intensive products. Under baseline conditions (i.e., today's climate and no change in the estimated availability of land over the period), 60 to 87 GtC could be conserved and sequestered over the period 1995 to 2050 by slowing deforestation and promoting natural forest regeneration. The tropics have the potential to conserve and sequester the largest quantity of carbon (80 percent of the global total in the forestry sector), more than half of which would be due to promoting forest regeneration and slowing deforestation. The temperate and boreal zones could sequester about 20 percent of the global total, mainly in North America, temperate-zone Asia, the former Soviet Union, China, and New Zealand. Projections of increased demand for agricultural land in the tropics could reduce these estimates significantly. 6.17 The cumulative cost, excluding land costs, to conserve and sequester the above amounts of carbon range from US$250 billion to $300 billion (thousand million) , at a unit cost ranging from $2 to $8/tonne of carbon. Realised costs will depend on national circumstances, including costs of land, establishment of infrastructure, tree nurseries, training programs and protection. Costs per unit of carbon sequestered or conserved generally increase from slowing deforestation to establishing plantations. 6.18 In agriculture, a variety of practices could increase storage of carbon. Recent studies indicate that 20-30 GtC could be sequestered through improved management of agricultural soils, including return of crop residues and reduced tillage. An additional9-37 Gt C could be sequestered due to restoration of degraded agricultural lands and improved management of rangelands. Reductions in methane and nitrous oxide emissions through improved management of agricultural practices 6.19 Emissions from the agriculture sector contribute now about one-fifth to overall anthropogenic emissions. This sector accounts for about 50% of anthropogenic methane, and about 70% of anthropogenic nitrous oxide, emissions. 6.20 Significant decreases in methane emissions from agriculture can be achieved through improved nutrition of ruminant animals and better management of paddy rice fields (e.g., irrigation, nutrients, use of new cultivars). Further methane reductions are possible with altered treatment and management of animal wastes and by reducing agricultural biomass burning. These practices could be combined to reduce methane emissions from agriculture by 25 to 100 Tg/yr (estimated annual anthropogenic methane emissions in the 1980s were 300-450 Tg/yr). The projected increase in world population during the next century would imply larger, however, methane emissions. 6.21 Sources of nitrous oxide in agriculture are mineral fertilisers, legume cropping, animal waste and biomass burning. The N2O emissions could be reduced by 0.3 to 0.9 Tg N/yr by improving fertiliser and manure- use efficiency with presently available techniques (estimated emissions in the 1980s were 3-8 Tg/yr). Other benefits of mitigation options 6.22 Measures to reduce greenhouse gas emissions often yield additional economic benefits (such as reduced traffic congestion) and/or environmental benefits (such as reduced emissions of urban smog precursors). What matters from a policy perspective is the net cost (total cost adjusted for other benefits and costs) of a mitigation or an adaptation option apart from its climate change benefits. The magnitude of these secondary benefits depends on local circumstances. Studies for European countries and the United States indicate that secondary benefits could offset 30% to 100% of abatement costs. For many countries and peoples there are problems which are perceived as being more pressing than potential climate change. These include provision of basic needs, and regional and local pollution. By raising efficiency and energy use, local and regional pollution can be curbed, and costs reduced, releasing financial and other resources for other needs. These are sometimes described as secondary benefits, although given the different local and regional priorities, they may in some countries well be considered primary benefits and climate change mitigation a valuable secondary benefit. Barriers to Implementing Mitigation Options 6.23 Historically, gaps have existed between the most cost-effective technologies available or rapidly becoming available and those actually in use. There are also gaps between what existing industrial plants and equipment should be able to achieve in terms of efficiency and what is actually being achieved. 6.24 There are time lags in exploiting new technologies, because of the risk of financial losses, if the new technology is introduced before earlier investments are fully amortized. Several other factors may be even greater discouragements: uncertainty about the costs of the new technology (operating and maintenance costs, reliability and training in of new skills) and the level of service provided; uncertainty about the long-term prices, lack of information, poor decision processes, imperfect market structures, institutional deficiencies including restrictive government regulations and property tenure; the status of economic and cultural development; the motivation for innovation, which is ultimately determined by prevailing incentive systems that are often based on societal values other than the risk of climate change. Addressing Barriers 6.25 Many policy instruments are available to facilitate the penetration of lower carbon intensity technologies and modified consumption patterns. They include energy pricing strategies, e.g., carbon or energy taxes and reduced energy subsidies, incentives such as provisions for accelerated depreciation and reduced cost for the consumers, tradable emission permits, reduction of market imperfections, negotiated agreements with industry, new standards and product labelling and increased support for research and development. (See chapter 11 of the contribution of Working Group III to the IPCC Second Assessment Report for more detailed analyses of the advantages and disadvantages of such instruments.) 6.26 The optimal mix of policy instruments will vary from country to country depending upon political structure and societal receptiveness. It will also vary between economic sectors and on whether or not there is a tradition of negotiated agreements between government and industry. 6.27 The best combination of policies will also vary over time. Studies indicate that high priority should initially be given to the removal of existing barriers, to the implementation of best available technologies, elimination of barriers due to existing investments in raw materials, processes and products, vested interests, institutional inertia and lack of information and awareness. The longer-run costs of abatement can be reduced by improved price signals, research and development and emphasis on effective information programmes. 6.28 No significant shift in technical consumption patterns towards low- emitting products and services is likely if relative prices do not encourage it. The impact of price signals, whether achieved through taxes or incentives or tradable permits, will ultimately depend on: continuity of the policy, including confidence in its long-run stability, prevention of "free riders", and progressiveness in implementation; the way in which revenues arising from the price signals are recycled in the economy. 6.29 The use of taxes to alter market prices requires careful consideration in order to avoid market distortions and decreasing economic efficiency, which could negate the overall impact of climate change policies. On the other hand, if the proceeds of a carbon tax are used to reduce other taxes which have a distortionary impact on labour and capital, an effective use of the tax might be achieved.. Such a move might simultaneously help to reduce long-term concerns about climate change with concern about unemployment and public expenditure levels and their allocation. Combining Mitigation Options 6.30 Each of the technologies and measures discussed above has the potential to contribute to the reduction of GHG emissions and the enhancement of GHG sinks. Evaluating the effectiveness of these individual options is relatively straightforward. However, understanding the overall effectiveness of combinations of these options to reduce energy demand and increase use of energy resources with lower emissions requires development and evaluation of an integrated mitigation strategy. There is no unique path to realization of deep emissions reductions. 6.31 Several modelling experiments suggest that achieving deep reductions in emissions is possible at low cost over the long term. However, it is not possible to identify a least-cost future energy system for the longer term, as the relative costs of options depend on resource constraints, technological opportunities that are imperfectly known and on actions to be taken by governments and the private sector. Published estimates of the cost of mitigating greenhouse gas emissions and increasing carbon sequestration vary substantially. Despite significant progress in reconciling methodological and technical differences concerning model structures and data, major differences concerning underlying assumptions remain. These differences reflect alternative perspectives about such factors as the efficiency of energy markets, distortions in fiscal systems, availability of new technologies and the costs o implementation. 7.1 Article 2 provides the framework for international cooperation in decision- making to address climate change. Article 3 sets out a number of principles for the implementation of the provisions of the Convention including Article 2. 7.2 Climate change presents the decision-maker with a formidable set of challenges: very long planning horizon; Large Uncertainties;
Long time scales of relevance suggest the need for early decision-making: (a) from emissions of greenhouse gases to the response of the climate system, (b) for adaptation of the ecosystems and natural resource systems to climate change, (c) for the climate system to come to equilibrium once greenhouse gas concentrations are stabilized, (d) for turnover of infrastructure and capital in the energy, industrial, transport and commercial/residential buildings sectors; and (e) the nature of international and national political processes. While knowledge about climate change, its potential effects, and the advantages and disadvantages of various responses is increasing, there are still critical uncertainties regarding basic scientific and socio-economic issues. These uncertainties make it difficult to assess the risks posed by anthropogenic climate change, and increase the costs of insurance and new infrastructure. Some potential impacts of climate change, such as loss of biological diversity and land, are irreversible. Some other impacts may be disproportionate to the changes in climate because of likely thresholds. Impacts and the costs of mitigation and adaptation will vary both within and among countries raising issues of intranational and international equity. Perceived equity is an important element for legitimizing decisions and promoting cooperation. Sustainable development is often defined as "meeting the needs of the present without compromising the ability of future generations to meet their own needs". Because future generations are not able to influence directly the actions taken that will affect their well-being, climate change raises issues of inter- generational equity. These issues are generally addressed through the choice of a discount rate. Making the choice is a question of values, a profound ethical question, since the choice inherently compares the costs of present measures against possible damages suffered by future generations if no action is taken. Economic efficiency requires that emission reductions occur where their cost is lowest, irrespective of who bears the financial burden. For purposes of analysis, it is useful to separate efficiency (what to do and how it is done) from equity (who bears the burden) considerations. This analytical separation can be implemented in practice only if effective institutions exist or can be created for appropriate redistribution of climate change costs. Measures to reduce greenhouse gas emissions and increase sinks can yield multiple additional benefits (e.g., rural employment generation, reduced traffic congestion, reduced emissions of urban smog precursors). The magnitude of these other benefits depends on local circumstances. When other priorities such as provision of basic needs or reducing regional or local pollution are perceived to be more important, actions taken to address them are generally likely to advance the goal of greenhouse gas mitigation simultaneously. Radiative forcing of climate warming is caused by anthropogenic emissions of other greenhouse gases in addition to CO2. Cooling due to anthropogenic aerosols should also be taken into account. To achieve stabilization of all greenhouse gas concentrations, the concept of equivalent CO2 can be used. It is possible to increase the efficiency of strategies to stabilize concentrations by reducing initially the emissions of those gases which have the lowest marginal costs of control. 7.4 A stabilization objective could be based upon a benefit-cost analysis, a cost-effectiveness approach or an absolute standard. Benefit-cost analysis or trade-off analysis attempts to identify the most efficient climate change strategy by balancing the costs of mitigation and adaptation measures against the damages avoided by these measures, including non-market costs such as damage to ecosystems or loss of species. 7.5 A cost-effectiveness approach would begin with a maximum atmospheric concentration of greenhouse gases, based on an assessment of the risks associated with different concentrations and the costs of achieving those concentrations. The objective would be reach the specified target at the lowest total cost, including non-market costs. 7.6 An absolute standard approach would define a maximum atmospheric concentration of greenhouse gases that is considered to constitute "dangerous anthropogenic interference with the climate system" on the basis of predicted biophysical impacts of climate change, independent of the economic and social impacts of achieving this concentration. Economists generally reject the absolute standard approach, believing that trade-offs are always relevant. At the same time, it is recognized that many governments set policies on the basis of underlying legislation that is itself based on an absolute standard. Even under the absolute standard approach, mitigation and adaptation measures should be chosen to achieve the standard at least cost. 7.7 Given the interrelated nature of the global economic system, attempts to mitigate climate change through actions in one region or sector may have offsetting effects which increase emissions from other regions or sectors. These emission reduction leakages can be reduced through coordinated actions of groups of countries. Considerations for moving towards the ultimate objective 7.8 Article 2 of the Convention introduces several specific considerations to be taken into account in moving towards stabilization of GHG concentrations. The ability of ecosystems to adapt naturally depends critically on the rate of climate change. Analyses suggest that in some regions significant reductions in food security may occur but that global food production may not be seriously threatened. Thus, with free, fair and unrestricted trade, food security is unlikely to be threatened by the risks of climate change due to a greenhouse warming. Economic development may not be able to proceed in a sustainable manner in those areas where climate change could worsen existing water and food shortages, public health concerns and exposure to natural disasters. 7.9 A number of levels for stabilization of greenhouse gas concentrations have been explored in the scientific literature. While some effects of different levels can be identified or inferred from this literature (for example, a rate of global mean temperature increase of 0.1 C per decade may result in significant loss of species from forest and montane ecosystems), there is not enough information to specify completely the consequences of various concentrations or emissions pathways for ecosystems, food production, or sustainable development. 7.10 Nonetheless, a number of observations of relevance to policymaking can be made about stabilization and potential options to achieve it: The impacts of stabilizing at a level of 750 ppmv (of equivalent CO2, implying a value for CO2 alone close to thrice its pre-industrial concentration) or higher are outside documented past fluctuations in greenhouse gas concentrations and climate and associated impacts; In order to achieve stabilization near or below 750 ppmv, emissions will have to fall substantially below those of the IPCC IS92a emissions scenario within the next few decades. Higher initial emissions would require more drastic reductions later to achieve stabilization; Stabilizing concentrations at any of the levels illustrated in this discussion requires initiation of near term measures including: (i) research and development on energy efficiency improvements, alternative sources of energy, and strategies to accelerate diffusion of new technologies into the market place; (ii) policies to encourage replacement of long-lived energy, transportation and industrial infrastructure in normal investment cycles with plant and equipment that provides the highest amount of service and the lowest level of greenhouse gas emissions per unit of input energy and materials; (iii) research and monitoring to promote a better understanding of the climate system and the impacts of climate variability; and (iv) action of other measures with multiple benefits and negative or low cost. Such measures would begin the process of moving towards eventual stabilization while further information is developed; Delaying action might conceivably reduce the overall costs of mitigation, but would increase both the rate and the eventual magnitude of climate change, and hence the adaptation and damage costs. 7.11 "No regrets" measures are those whose benefits, such as reduced energy costs and lower emissions of local and regional pollutants, equal or exceed their cost to society, excluding the benefits of mitigation of climate change. Such "no regrets" mitigation and adaptation measures would appear justified on technical grounds unrelated to the risks of rapid climate change due to greenhouse gases. The expectation of net damages from climate change and the precautionary principle provide a rationale for going beyond "no regrets". 7.12 A sequential decision-making approach offers a prudent strategy that can be adjusted in the light of new information and could take into account factors such as future flexibility and current and future costs. Near term decisions along an optimal path (i.e., modest cost mitigation measures) will be the same for a wide range of ultimate stabilization concentrations (see chapter 5 also). 7.13 A broad portfolio of actions aimed at mitigation, adaptation and reducing uncertainties through further research provides a balanced approach to managing the risks of anthropogenic climate change. The appropriate portfolio will differ from country to country. A well-chosen portfolio of climate change investments will yield greater benefit for a given cost than any one option undertaken by itself.
The Rivers Council of Minnesota
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