1.1 Following a resolution of the Executive Council of the World

Meteorological Organization (July 1992), the IPCC decided to include

an examination of approaches to Article 2, the Objective of the

UN Framework Convention on Climate Change (UNFCCC), in its work

programme. It organized a workshop on the subject in October 1994

in Fortaleza, Brazil, at the invitation of the Government of Brazil.

Thereafter, the IPCC Chairman assembled a team of lead authors

(listed at the end of this report) under his chairmanship to draft

the Synthesis. The team produced the draft which was submitted

for expert and government review and comment. The final draft

Synthesis was approved line-by-line by the IPCC at its eleventh

session (Rome, 11-15 December 1995), where representatives of

116 governments were present as well as 13 intergovernmental and

25 non-governmental organizations. It may be noted for information

that all Member States of the World Meteorological Organization

and of the United Nations are Members of the IPCC and can attend

its sessions and those of its Working Groups. The Synthesis presents

information on the scientific and technical issues related to

interpreting Article 2 of the UN FCCC, drawing on the underlying

IPCC Second Assessment Report. Since the Synthesis is not simply

a summary of the IPCC Second Assessment Report, the Summaries

for Policymakers of the three IPCC Working Groups should also

be consulted for a summary of the Second Assessment Report.



1.2 During the past few decades, two important factors regarding

the relationship between humans and the Earth's climate have become

apparent. First, human activities, including the burning of fossil

fuels, land-use change and agriculture, are increasing the atmospheric

concentrations of greenhouse gases (which tend to warm the atmosphere)

and, in some regions, aerosols (microscopic airborne particles,

which tend to cool the atmosphere). These changes in greenhouse

gases and aerosols, taken together, are projected to change regional

and global climate and climate-related parameters such as temperature,

precipitation, soil moisture and sea level. Second, some human

communities have become more vulnerable to hazards such as storms,

floods and droughts as a result of increasing population density

in sensitive areas such as river basins and coastal plains. Potentially

serious changes have been identified, including an increase in

some regions in the incidence of extreme high-temperature events,

floods and droughts, with resultant consequences for fires, pest

outbreaks, and ecosystem composition, structure and functioning,

including primary productivity.



1.3 Scientific and technical assessments of climate change and

its impacts have been conducted by the Intergovernmental Panel

on Climate Change (IPCC). The First Assessment, published in 1990,

provided a scientific and technical base for the UN Framework

Convention on Climate Change (FCCC) which was open for signature

at the Earth Summit in Rio in 1992.



1.4 The ultimate objective of the FCCC, as expressed in 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, to ensure that food production is not threatened

and to enable economic development to proceed in a sustainable

manner".



1.5 The challenges presented to the policymaker by Article 2 are

the determination of what concentrations of greenhouse gases might

be regarded as "dangerous anthropogenic interference with

the climate system" and the charting of a future which allows

for economic development which is sustainable. The purpose of

this synthesis report is to provide scientific, technical and

socio-economic information that can be used, inter alia, in addressing

these challenges. It is based on the 1994 and 1995 reports of

the IPCC Working Groups.



1.6 The report follows through the various matters which are addressed

in Article 2. It first briefly summarizes the degree of climate

change - the "interference with the climate system"

- which is projected to occur as a result of human

activities. It then goes on to highlight what we know about the

vulnerabilities of ecosystems and human communities to likely

climate changes, especially in regard to agriculture and food

production and to other factors such as water availability, health

and the impact of sea level rise which are important considerations

for sustainable development. The task of the IPCC is to provide

a sound scientific basis that would enable policymakers to better

interpret dangerous anthropogenic interference with the climate

system.



1.7 Given current trends of increasing emissions of most greenhouse

gases, atmospheric concentrations of these gases will increase

through the next century and beyond. With the growth in atmospheric

concentrations of greenhouse gases, interference with the climate

system will grow in magnitude, and the likelihood of adverse impacts

from climate change that could be judged dangerous will become

greater. Therefore, possible pathways of future net emissions

were considered which might lead to stabilization at different

levels and the general constraints these imply. This consideration

forms the next part of the report and is followed by a summary

of the technical and policy options for reducing emissions and

enhancing sinks of greenhouse gases.



1.8 The report then addresses issues related to equity and to

ensuring that economic development proceeds in a sustainable manner.

This involves addressing, for instance, estimates of the likely

damage of climate change impacts, and the impacts, including costs

and benefits, of adaptation and mitigation. Finally, a number

of insights from available studies point to ways of taking initial

actions (see the section on Road Forward) even if, at present,

it is difficult to decide upon a target for atmospheric concentrations,

including considerations of time-frames, that would prevent "dangerous

anthropogenic interference with the climate system".



1.9 Climate change presents the decision maker with a set of formidable

complications: considerable remaining uncertainties inherent in

the complexity of the problem, the potential for irreversible

damages or costs, a very long planning horizon, long time lags

between emissions and effects, wide regional variations in causes

and effects, an irreducibly global problem, and a multiple of

greenhouse gases and aerosols to consider. Yet another complication

is that effective protection of the climate system requires international

cooperation in the context of wide variations in income levels,

flexibility, and expectations of the future; this raises issues

of efficiency and intra-national, international and intergenerational

equity. Equity is an important element for legitimizing decisions

and promoting cooperation.



1.10 Decisions with respect to Article 2 of the FCCC involve three

distinct but interrelated choices: stabilization level, net emissions

pathway and mitigation technologies and policies. The report presents

available scientific and technical information on these three

choices. It also notes where uncertainties remain regarding such

information. Article 3 of the FCCC identifies a range of principles

that shall guide, inter alia, decision making with respect

to the ultimate objective of the Convention, as found in Article

2. Article 3.3 provides guidance, inter alia, on decision

making where there is a lack of full scientific certainty, namely

that 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."



The Second Assessment Report of the IPCC also provides information

in this regard.



The long time scales involved in the climate system (e.g.,

the long residence time of greenhouse gases in the atmosphere)

and in the time for replacement of infrastructure, and the lag

by many decades to centuries between stabilization of concentrations

and stabilization of temperature and mean sea level, indicate

the importance for timely decision-making.



2. ANTHROPOGENIC INTERFERENCE WITH THE CLIMATE SYSTEM 


Interference to the present day



2.1 In order to understand what constitutes concentrations of

greenhouse gases that would prevent dangerous interference with

the climate system, it is first necessary to understand current

atmospheric concentrations and trends of greenhouse gases, and

their consequences (both present and projected) to the climate

system.



2.2 The atmospheric concentrations of the greenhouse gases, and

among them, carbon dioxide (CO2), methane (CH4) and nitrous oxide

(N2O), have grown significantly since pre-industrial times (about

1750 A.D): CO2 from about 280 to almost 360 ppmv, CH4 from 700

to 1720 ppbv and N2O from about 275 to about 310 ppbv. These trends

can be attributed largely to human activities, mostly fossil fuel

use, land-use change and agriculture. Concentrations of other

anthropogenic greenhouse gases have also increased. An increase

of greenhouse gas concentrations leads on average to an additional

warming of the atmosphere and the Earth's surface. Many greenhouse

gases remain in the atmosphere - and affect climate - for a long

time.



2.3 Tropospheric aerosols resulting from combustion of fossil

fuels, biomass burning and other sources have led to a negative

direct forcing and possibly also to a negative indirect forcing

of a similar magnitude. While the negative forcing is focused

in particular regions and subcontinental areas, it can have continental

to hemispheric scale effects on climate patterns. Locally, the

aerosol forcing can be large enough to more than offset the positive

forcing due to greenhouse gases. In contrast to the long-lived

greenhouse gases, anthropogenic aerosols are very short-lived

in the atmosphere and hence their radiative forcing adjusts rapidly

to increases or decreases in emissions.



2.4 Global mean surface temperature has increased by between about

0.3 and 0.6°C since the late 19th century, a change that

is unlikely to be entirely natural in origin. The balance of evidence,

from changes in global mean surface air temperature and from changes

in geographical, seasonal and vertical patterns of atmospheric

temperature, suggests a discernible human influence on global

climate. There are uncertainties in key factors, including the

magnitude and patterns of long-term natural variability. Global

sea level has risen by between 10 and 25 cm over the past 100

years and much of the rise may be related to the increase in global

mean temperature.



2.5 There are inadequate data to determine whether consistent

global changes in climate variability or weather extremes have

occurred over the 20th century. On regional scales there is clear

evidence of changes in some extremes and climate variability indicators.

Some of these changes have been toward greater variability, some

have been toward lower variability. However, to-date it has not

been possible to firmly establish a clear connection between these

regional changes and human activities.



Possible consequences of future interference



2.6 In the absence of mitigation policies or significant technological

advances that reduce emissions and/or enhance sinks, concentrations

of greenhouse gases and aerosols are expected to grow throughout

the next century. The IPCC has developed a range of scenarios

, IS92 a-f, of future greenhouse gas and aerosol precursor emissions

based on assumptions concerning population and economic growth,

land-use, technological changes, energy availability and fuel

mix during the period 1990 to 2100. By the year 2100, carbon dioxide

emissions under these scenarios are projected to be in the range

of about 6 GtC per year, roughly equal to current emissions, to

as much as 36 GtC per year, with the lower end of the IPCC range

assuming low population and economic growth to 2100. Methane emissions

are projected to be in the range 540 to 1170 Tg CH4 per year (1990

emissions were about 500 Tg CH4); nitrous oxide emissions are

projected to be in the range 14 to 19 Tg N per year (1990 emissions

were about 13 Tg N). In all cases, the atmospheric concentrations

of greenhouse gases and total radiative forcing continue to increase

throughout the simulation period of 1990 to 2100.



2.7 For the mid-range IPCC emission scenario, IS92a, assuming

the "best estimate" value of climate sensitivity and

including the effects of future increases in aerosol concentrations,

models project an increase in global mean surface temperature

relative to 1990 of about 2oC by 2100. This estimate is approximately

one third lower than the "best estimate" in 1990. This

is due primarily to lower emission scenarios (particularly for

CO2 and CFCs), the inclusion of the cooling effect of sulphate

aerosols, and improvements in the treatment of the carbon cycle.

Combining the lowest IPCC emission scenario (IS92c) with a "low"

value of climate sensitivity and including the effects of future

changes in aerosol concentrations leads to a projected increase

of about 1oC by 2100. The corresponding projection for the highest

IPCC scenario (IS92e) combined with a "high" value of

climate sensitivity gives a warming of about 3.5oC. In all cases

the average rate of warming would probably be greater than any

seen in the last 10,000 years, but the actual annual to decadal

changes would include considerable natural variability. Regional

temperature changes could differ substantially from the global

mean value. Because of the thermal inertia of the oceans, only

50-90% of the eventual equilibrium temperature change would have

been realised by 2100 and temperature would continue to increase

beyond 2100, even if concentration of greenhouse gases were stabilised

by that time.



2.8 Average sea level is expected to rise as a result of thermal

expansion of the oceans and melting of glaciers and ice-sheets.

For the IS92a scenario, assuming the "best estimate"

values of climate sensitivity and of ice melt sensitivity to warming,

and including the effects of future changes in aerosol concentrations,

models project an increase in sea level of about 50 cm from the

present to 2100. This estimate is approximately 25% lower than

the "best estimate" in 1990 due to the lower temperature

projection, but also reflecting improvements in the climate and

ice melt models. Combining the lowest emission scenario (IS92c)

with the "low" climate and ice melt sensitivities and

including aerosol effects gives a projected sea level rise of

about 15 cm from the present to 2100. The corresponding projection

for the highest emission scenario (IS92e) combined with "high"climate

and ice-melt sensitivities gives a sea level rise of about 95

cm from the present to 2100. Sea level would continue to rise

at a similar rate in future centuries beyond 2100, even if concentrations

of greenhouse gases were stabilised by that time, and would continue

to do so even beyond the time of stabilisation of global mean

temperature. Regional sea level changes may differ from the global

mean value owing to land movement and ocean current changes.



2.9 Confidence is higher in the hemispheric-to-continental scale

projections of coupled atmosphere-ocean climate models than in

the regional projections, where confidence remains low. There

is more confidence in temperature projections than hydrological

changes.



2.10 All model simulations, whether they were forced with increased

concentrations of greenhouse gases and aerosols or with increased

concentrations of greenhouse gases alone, show the following features:

greater surface warming of the land than of the sea in winter;

a maximum surface warming in high northern latitudes in winter,

little surface warming over the Arctic in summer; an enhanced

global mean hydrological cycle, and increased precipitation and

soil moisture in high latitudes in winter. All these changes are

associated with identifiable physical mechanisms.



2.11 Warmer temperatures will lead to a more vigorous hydrological

cycle; this translates into prospects for more severe droughts

and/or floods in some places and less severe droughts and/or floods

in other places. Several models indicate an increase in precipitation

intensity, suggesting a possibility for more extreme rainfall

events. Knowledge is currently insufficient to say whether there

will be any changes in the occurrence or geographical distribution

of severe storms, e.g., tropical cyclones.



2.12 There are many uncertainties and many factors currently limit

our ability to project and detect future climate change. Future

unexpected, large and rapid climate system changes (as have occurred

in the past) are, by their nature difficult to predict. This implies

that future climate changes may also involve "surprises".

In particular, these arise from the non-linear nature of the climate

system. When rapidly forced, non-linear systems are especially

subject to unexpected behaviour. Progress can be made by investigating

non-linear processes and sub-components of the climatic system.

Examples of such non-linear behaviour include rapid circulation

changes in the North Atlantic and feedbacks associated with terrestrial

ecosystem changes.





3. SENSITIVITY AND ADAPTATION OF SYSTEMS TO CLIMATE CHANGE







3.1 This section provides scientific and technical information

that can be used, inter alia, in evaluating whether the projected

range of plausible impacts constitutes "dangerous anthropogenic

interference with the climate system", as referred to in

Article 2, and in evaluating adaptation options. However, it is

not yet possible to link particular impacts with specific atmospheric

concentrations of greenhouse gases.



3.2 Human health, terrestrial and aquatic ecological systems,

and socioeconomic systems (e.g., agriculture, forestry, fisheries,

and water resources) are all vital to human development and well-being

and are all sensitive to both the magnitude and the rate of climate

change. Whereas many regions are likely to experience the adverse

effects of climate change - some of which are potentially irreversible

- some effects of climate change are likely to be beneficial.

Hence, different segments of society can expect to confront a

variety of changes and the need to adapt to them.



3.3 Human-induced climate change represents an important additional

stress, particularly to the many ecological and socioeconomic

systems already affected by pollution, increasing resource demands,

and non-sustainable management practices. The vulnerability of

human health and socioeconomic systems - and, to a lesser extent,

ecological systems - depends upon economic circumstances and institutional

infrastructure. This implies that systems typically are more vulnerable

in developing countries where economic and institutional circumstances

are less favourable.



3.4 Although our knowledge has increased significantly during

the last decade and qualitative estimates can be developed, quantitative

projections of the impacts of climate change on any particular

system at any particular location are difficult because regional-scale

climate change projections are uncertain; our current understanding

of many critical processes is limited; systems are subject to

multiple climatic and non-climatic stresses, the interactions

of which are not always linear or additive; and very few studies

have considered dynamic responses to steadily increasing concentrations

of greenhouse gases or the consequences of increases beyond a

doubling of equivalent atmospheric CO2 concentrations.



3.5 Unambiguous detection of climate-induced changes in most ecological

and social systems will prove extremely difficult in the coming

decades. This is because of the complexity of these systems, their

many non-linear feedbacks, and their sensitivity to a large number

of climatic and non-climatic factors, all of which are expected

to continue to change simultaneously. As future climate extends

beyond the boundaries of empirical knowledge (i.e., the documented

impacts of climate variation in the past), it becomes more likely

that actual outcomes will include surprises and unanticipated

rapid changes.



Sensitivity of Systems



Terrestrial and Aquatic Ecosystems



3.6 Ecosystems contain the Earth's entire reservoir of genetic

and species diversity and provide many goods and services including:

(i) providing food, fibre, medicines, and energy; (ii) processing

and storing carbon and other nutrients; (iii) assimilating wastes,

purifying water, regulating water runoff, and controlling floods,

soil degradation and beach erosion; and (iv) providing opportunities

for recreation and tourism. The composition and geographic distribution

of many ecosystems (e.g., forests, rangelands, deserts, mountain

systems, lakes, wetlands, and oceans) will shift as individual

species respond to changes in climate; there will likely be reductions

in biological diversity and in the goods and services that ecosystems

provide society. Some ecological systems may not reach a new equilibrium

for several centuries after the climate achieves a new balance.

This section illustrates the impact of climate change on a number

of selected ecological systems.



3.7 Forests: Models project that as a consequence of possible

changes in temperature and water availability under doubled equivalent

CO2 equilibrium conditions, a substantial fraction (a global average

of one-third, varying by region from one-seventh to two-thirds)

of the existing forested area of the world will undergo major

changes in broad vegetation types - with the greatest changes

occurring in high latitudes and the least in the tropics. Climate

change is expected to occur at a rapid rate relative to the speed

at which forest species grow, reproduce, and reestablish themselves.

Therefore, the species composition of forests is likely to change;

entire forest types may disappear, while new assemblages of species

and hence new ecosystems may be established. Large amounts of

carbon could be released into the atmosphere during transitions

from one forest type to another because the rate at which carbon

can be lost during times of high forest mortality is greater than

the rate at which it can be gained through growth to maturity.



3.8 Deserts and desertification: Deserts are likely to

become more extreme - in that, with few exceptions, they are projected

to become hotter but not significantly wetter. Temperature increases

could be a threat to organisms that exist near their heat tolerance

limits. Desertification - land degradation in arid, semi-arid

and dry sub-humid areas resulting from various factors, including

climatic variations and human activities - is more likely to become

irreversible if the environment becomes drier and the soil becomes

further degraded through erosion and compaction.



3.9 Mountain ecosystems: The altitudinal distribution of

vegetation is projected to shift to higher elevation; some species

with climatic ranges limited to mountain tops could become extinct

because of disappearance of habitat or reduced migration potential.



3.10 Aquatic and coastal ecosystems: In lakes and streams,

warming would have the greatest biological effects at high latitudes,

where biological productivity would increase, and at the low-latitude

boundaries of cold- and coolwater species ranges, where extinctions

would be greatest. The geographical distribution of wetlands is

likely to shift with changes in temperature and precipitation.

Coastal systems are economically and ecologically important and

are expected to vary widely in their response to changes in climate

and sea level. Some coastal ecosystems are particularly at risk,

including saltwater marshes, mangrove ecosystems, coastal wetlands,

sandy beaches, coral reefs, coral atolls, and river deltas. Changes

in these ecosystems would have major negative effects on tourism,

freshwater supplies, fisheries, and biodiversity.



Hydrology and Water Resources Management



3.11 Models project that between one-third and one-half of existing

mountain glacier mass could disappear over the next hundred years.

The reduced extent of glaciers and depth of snow cover also would

affect the seasonal distribution of river flow and water supply

for hydroelectric generation and agriculture. Anticipated hydrological

changes and reductions in the areal extent and depth of permafrost

could lead to large-scale damage to infrastructure, an additional

flux of carbon dioxide into the atmosphere, and changes in processes

that contribute to the flux of methane into the atmosphere.



3.12 Climate change will lead to an intensification of the global

hydrological cycle and can have major impacts on regional water

resources. Changes in the total amount of precipitation and in

its frequency and intensity directly affect the magnitude and

timing of runoff and the intensity of floods and droughts; however,

at present, specific regional effects are uncertain. Relatively

small changes in temperature and precipitation, together with

the non-linear effects on evapotranspiration and soil moisture,

can result in relatively large changes in runoff, especially in

arid and semi-arid regions. The quantity and quality of water

supplies already are serious problems today in many regions, including

some low-lying coastal areas, deltas, and small islands, making

countries in these regions particularly vulnerable to any additional

reduction in indigenous water supplies.



Agriculture and Forestry



3.13 Crop yields and changes in productivity due to climate change

will vary considerably across regions and among localities, thus

changing the patterns of production. Productivity is projected

to increase in some areas and decrease in others, especially the

tropics and subtropics. Existing studies show that on the whole,

global agricultural production could be maintained relative to

baseline production in the face of climate change projected under

doubled equivalent CO2 equilibrium conditions. This conclusion

takes into account the beneficial effects of CO2 fertilization

but does not allow for changes in agricultural pests and the possible

effects of changing climatic variability. However, focusing on

global agricultural production does not address the potentially

serious consequences of large differences at local and regional

scales, even at mid-latitudes. There may be increased risk of

hunger and famine in some locations; many of the world's poorest

people - particularly those living in subtropical and tropical

areas and dependent on isolated agricultural systems in semi-arid

and arid regions - are most at risk of increased hunger. Global

wood supplies during the next century may become increasingly

inadequate to meet projected consumption due to both climatic

and non-climatic factors.



Human Infrastructure



3.14 Climate change clearly will increase the vulnerability of

some coastal populations to flooding and erosional land loss.

Estimates put about 46 million people per year currently at risk

of flooding due to storm surges. In the absence of adaptation

measures, and not taking into account anticipated population growth,

50-cm sealevel rise would increase this number to about 92 million;

a 1-meter sea-level rise would raise it to about 118 million.

Studies using a 1-meter projection show a particular risk for

small islands and deltas. This increase is at the top range of

IPCC Working Group I estimates for 2100; it should be noted, however,

that sea level is actually projected to continue to rise in future

centuries beyond 2100. Estimated land losses range from 0.05%

in Uruguay, 1.0% for Egypt, 6% for the Netherlands, and 17.5%

for Bangladesh to about 80% for the Majuro Atoll in the Marshall

Islands, given the present state of protection systems. Some small

island nations and other countries will confront greater vulnerability

because their existing sea and coastal defense systems are less

well-established. Countries with higher population densities would

be more vulnerable. Storm-surges and flooding could threaten entire

cultures. For these countries, sea-level rise could force internal

or international migration of populations.



Human Health



3.15 Climate change is likely to have wide-ranging and mostly

adverse impacts on human health, with significant loss of life.

Direct health effects include increases in (predominantly cardio-respiratory)

mortality and illness due to an anticipated increase in the intensity

and duration of heat waves. Temperature increases in colder regions

should result in fewer cold-related deaths. Indirect effects of

climate change, which are expected to predominate, include increases

in the potential transmission of vector-borne infectious diseases

(e.g., malaria, dengue, yellow fever, and some viral encephalitis)

resulting from extensions of the geographical range and season

for vector organisms. Models (that entail necessary simplifying

assumptions) project that temperature increases of 3-5° C

(compared to the IPCC projection of 1-3.5° C by 2100) could

lead to potential increases in malaria incidence (of the order

of 50-80 million additional annual cases, relative to an assumed

global background total of 500 million cases), primarily in tropical,

subtropical, and less well-protected temperate-zone populations.

Some increases in non-vector-borne infectious diseases - such

as salmonellosis, cholera, and giardiasis - also could occur as

a result of elevated temperatures and increased flooding. Limitations

on freshwater supplies and on nutritious food, as well as the

aggravation of air pollution, will also have human health consequences.



3.16 Quantifying the projected impacts is difficult because the

extent of climate-induced health disorders depends on numerous

coexistent and interacting factors that characterize the vulnerability

of the particular population, including environmental and socioeconomic

circumstances, nutritional and immune status, population density,

and access to quality health care services. Hence, populations

with different levels of natural, technical, and social resources

would differ in their vulnerability to climate-induced health

impacts.



Technology and Policy Options for Adaptation



3.17 Technological advances generally have increased adaptation

options for managed systems. Adaptation options for freshwater

resources include more efficient management of existing supplies

and infrastructure; institutional arrangements to limit future

demands/promote conservation; improved monitoring and forecasting

systems for floods/droughts; rehabilitation of watersheds, especially

in the tropics; and construction of new reservoir capacity. Adaptation

options for agriculture - such as changes in types and varieties

of crops, improved water-management and irrigation systems, and

changes in planting schedules and tillage practices - will be

important in limiting negative effects and taking advantage of

beneficial changes in climate. Effective coastal-zone management

and land-use planning can help direct population shifts away from

vulnerable locations such as flood plains, steep hillsides, and

low-lying coastlines. Adaptive options to reduce health impacts

include protective technology (e.g., housing, air conditioning,

water purification, and vaccination), disaster preparedness, and

appropriate health care.



However, many regions of the world currently have limited

access to these technologies and appropriate information. For

some island nations, the high cost of providing adequate protection

would make it essentially infeasible, especially given the limited

availability of capital for investment. The efficacy and cost-effective

use of adaptation strategies will depend upon the availability

of financial resources, technology transfer, and cultural, educational,

managerial, institutional, legal, and regulatory practices, both

domestic and international in scope. Incorporating climate-change

concerns into resource-use and development decisions and plans

for regularly scheduled investments in infrastructure will facilitate

adaptation.



4. ANALYTICAL APPROACH TO STABILIZATION OF ATMOSPHERIC CONCENTRATIONS

OF GREENHOUSE GASES 



4.1 Article 2 of the UN Framework Convention on Climate Change

refers explicitly to "stabilization of greenhouse gas concentrations".

This section provides information on the relative importance of

various greenhouse gases to climate forcing and discusses how

greenhouse gas emissions might be varied to achieve stabilization

at selected atmospheric concentration levels.



4.2 Carbon dioxide, methane and nitrous oxide have natural as

well as anthropogenic origins. The anthropogenic emissions of

these gases have contributed about 80% of the additional climate

forcing due to greenhouse gases since pre-industrial times (i.e.

since about 1750 A.D). The contribution of CO2 is about 60% of

this forcing, about four times that from CH4.



4.3 Other greenhouse gases include tropospheric ozone (whose chemical

precursors include nitrogen oxides, non-methane hydrocarbons and

carbon monoxide), halocarbons (including HCFCs and HFCs) and SF6.

Tropospheric aerosols and tropospheric ozone are inhomogeneously

distributed in time and space and their atmospheric lifetimes

are short (days to weeks). Sulphate aerosols are amenable to abatement

measures and such measures are presumed in the IPCC scenarios.



4.4 Most emission scenarios indicate that, in the absence of mitigation

policies, greenhouse gas emissions will continue to rise during

the next century and lead to greenhouse gas concentrations that

by the year 2100 are projected to change climate more than that

projected for twice the pre-industrial concentrations of carbon

dioxide.



Stabilization of Greenhouse Gases



4.5 All relevant greenhouse gases need to be considered in addressing

stabilisation of greenhouse gas concentrations. First carbon dioxide

is considered which, because of its importance and complicated

behaviour, needs more detailed consideration than the other greenhouse

gases.



Carbon dioxide



4.6 Carbon dioxide is removed from the atmosphere by a number

of processes that operate on different timescales. It has a relatively

long residence time in the climate system - of the order of a

century or more. If net global anthropogenic emissions (i.e. anthropogenic

sources minus anthropogenic sinks) were maintained at current

levels (about 7 GtC/yr including emissions from fossil fuel combustion,

cement production and land-use change), they would lead to a nearly

constant rate of increase in atmospheric concentrations for at

least two centuries, reaching about 500 ppmv (approaching twice

the pre-industrial concentration of 280 ppmv) by the end of the

21st century. Carbon cycle models show that immediate stabilisation

of the concentration of carbon dioxide at its present level could

only be achieved through an immediate reduction in its emissions

of 50-70% and further reductions thereafter.



4.7 Carbon cycle models have been used to estimate profiles of

carbon dioxide emissions for stabilization at various carbon dioxide

concentration levels. Such profiles have been generated for an

illustrative set of levels: 450, 550, 650, 750 and 1000 ppmv.

Among the many possible pathways to reach stabilization, two are

illustrated in Figure 1 for each of the stabilization levels of

450, 550, 650 and 750 ppmv, and one for 1000 ppmv. The steeper

the increase in the emissions (hence concentration) in these scenarios,

the more quickly is the climate projected to change.



4.8 Any eventual stabilised concentration is governed more by

the accumulated anthropogenic carbon dioxide emissions from now

until the time of stabilisation, than by the way those emissions

change over the period. This means that, for a given stabilised

concentration value, higher emissions in early decades require

lower emissions later on. Cumulative emissions from 1991 to 2100

corresponding to these stabilization levels are shown in Table

1, together with the cumulative emissions of carbon dioxide for

all of the IPCC IS92 emission scenarios (see Figure 2 below and

Table SPM-1 in the Summary for Policymakers of IPCC Working Group

II for details of these scenarios).



4.9 Figure 1 and Table 1 are presented to clarify some of the

constraints that would be imposed on future carbon dioxide emissions,

if stabilization at the concentration levels illustrated were

to be achieved. These examples do not represent any form of recommendation

about how such stabilization levels might be achieved or the level

of stabilization which might be chosen.



Figure 1 (a) Carbon dioxide concentration profiles leading

to stabilisation at 450, 550, 650 and 750 ppmv following the pathways

defined in IPCC (1994) (solid curves) and for pathways that allow

emissions to follow IS92a until at least the year 2000 (dashed

curves). A single profile that stabilises at a carbon dioxide

concentration of 1000 ppmv and follows IS92a emissions until at

least the year 2000 has also been defined. Stabilisation at concentrations

of 450, 650 and 1000 ppmv would lead to equilibrium temperature

increases relative to 1990 due to carbon dioxide alone (i.e. not

including effects of other GHGs and aerosols) of about 1°C

(range: 0.5 to 1.5°C); 2°C (range: 1.5 to 4°C)

and 3.5 °C (range: 2 to 7°C) respectively. A doubling

of the pre-industrial carbon dioxide concentration of 280 ppmv

would lead to a concentration of 560 ppmv and doubling of the

current concentration of 358 ppmv would lead to a concentration

of about 720 ppmv.



Figure 1 (b) Carbon dioxide emissions leading to stabilisation

at concentrations of 450, 550, 650, 750 and 1000 ppmv following

the profiles shown in (a) from a mid-range carbon cycle model.

Results from other models could differ from those presented here

by up to approximately ±15%. For comparison the carbon dioxide

emissions for IS92a and current emissions (fine solid line) are

also shown.



Figure 2 Annual anthropogenic carbon dioxide emissions

under the IS92 emission scenarios (see Table SPM-1 in the Summary

for Policymakers of IPCC Working Group II for further details).



Table 1 Total anthropogenic carbon dioxide emissions accumulated

from 1991 to 2100 inclusive (GtC) for the IS92 scenarios (see

Table SPM-1 in the Summary for Policymakers of IPCC Working Group

II) and for stabilisation at various levels of carbon dioxide

concentration following the two sets of pathways shown in Figure

1 (a). The accumulated emissions leading to stabilisation of carbon

dioxide concentration were calculated using a mid-range carbon

cycle model. Results from other models could be up to approximately

15% higher or lower than those presented here.



                         Accumulated carbon dioxide
emissions 1991 to 2100 (GtC) §



IS92 scenarios



c                    770



d                    980



b                    1430



a                    1500



f                    1830



e                    2190



Stabilization case     For profiles A*   For profiles B†





450 ppmv                630                650



550 ppmv                 870                990



650 ppmv                1030               1190



750 ppmv               1200‡              1300‡



1000 ppmv                 -                1410‡





§ For comparison, emissions during the period 1860 to 1994

amounted to about 360 GtC, of which about 240 GtC were due to

fossil fuel use and 120 GtC due to deforestation and land-use

change.



* As in IPCC (1994) - see figure 1 (a) (solid curves).



† Profiles that allow emissions to follow IS92a until at

least the year 2000 - see figure 1 (a) (dashed curves).



‡ Concentrations will not stabilise by 2100.



4.10 Given cumulative emissions, and IPCC IS92a population and

economic scenarios for 1990-2100, global annual average carbon

dioxide emissions can be derived for the stabilization scenarios

on a per capita or per unit of economic activity basis. If the

atmospheric concentration is to remain below 550 ppmv, the future

global annual average emissions cannot, during the next century,

exceed the current global average and would have to be much lower

before and beyond the end of the next century. Global annual average

emissions could be higher for stabilization levels of 750 to 1000

ppmv. Nevertheless, even to achieve these latter stabilization

levels, the global annual average emissions would need to be less

than 50% above current levels on a per capita basis or less than

half of current levels per unit of economic activity.



4.11 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, a net of about 0.2 tonnes

per capita are emitted from deforestation and land-use change.

The average annual fossil fuel per capita emission in developed

and transitional economy countries is about 2.8 tonnes and ranges

from 1.5 to 5.5 tonnes. The figure for the developing countries

is 0.5 tonnes ranging from 0.1 tonnes to, in some few cases, above

2.0 tonnes (all figures are for 1990).



4.12 Using World Bank estimates of GDP (gross domestic product)

at market exchange rates, the current global annual average emission

of energy-related carbon dioxide is about 0.3 tonnes per thousand

1990 US dollars output. In addition, global net emissions from

land use changes are about 0.05 tonnes per thousand US dollars

of output. The current average annual energy-related emissions

per thousand 1990 US dollars output, evaluated at market exchange

rates, is about 0.27 tonnes in developed and transitional economy

countries and about 0.41 tonnes in developing countries. Using

World Bank estimates of GDP at purchasing power parity exchange

rates, the average annual energy-related emissions per thousand

1990 US dollars output is about 0.26 tonnes in developed and transitional

economy countries and about 0.16 tonnes in developing countries.



Methane



4.13 Atmospheric methane concentrations adjust to changes in anthropogenic

emissions over a period of 9 to 15 years. If the annual methane

emissions were immediately reduced by about 30 Tg CH4 (about 8%

of current anthropogenic emissions) methane concentrations would

remain at today's levels. If methane emissions were to remain

constant at their current levels, its concentration (1720 ppbv

in 1994) would rise to about 1820 ppbv over the next 40 years.



Nitrous oxide



4.14 Nitrous oxide has a long lifetime (about 120 years) In order

for the concentration to be stabilized near current levels (312

ppbv in 1994), anthropogenic sources would need to be reduced

immediately by more than 50%. If emissions of nitrous oxide were

held constant at current levels, its concentration would rise

to about 400 ppbv over several hundred years, which would increase

its incremental radiative forcing by a factor of four over its

current level.



Further points on stabilization



4.15 Stabilization of the concentrations of very long-lived gases,

such as SF6 or perfluorocarbons, can only be achieved effectively

by stopping emissions.



4.16 The importance of the contribution of CO2 to climate forcing,

relative to that of the other greenhouse gases, increases with

time in all of the IS92 emission scenarios (a to f). For example,

in the IS92a scenario, the CO2 contribution increases from the

present 60% to about 75% by the year 2100. During the same period,

methane and nitrous oxide forcings increase in absolute terms

by a factor that ranges between two and three.



4.17 The combined effect of all greenhouse gases in producing

radiative forcing is often expressed in terms of the equivalent

concentration of carbon dioxide which would produce the same forcing.

Because of the effects of the other greenhouse gases, stabilisation

at some level of equivalent carbon dioxide concentration implies

maintaining carbon dioxide concentration at a lower level.



The stabilization of greenhouse gas concentrations does not

imply that there will be no further climate change. After stabilization

is achieved, global mean surface temperature would continue to

rise for some centuries and sea level for many centuries.



5. TECHNOLOGY AND POLICY OPTIONS FOR MITIGATION 



5.1 The IPCC Second Assessment Report (1995) examines a wide range

of approaches to reduce emissions and enhance sinks of greenhouse

gases. This section provides technical information on options

that could be used to reduce anthropogenic emissions and enhance

sinks of the principal greenhouse gases with a view to stabilizing

their atmospheric concentrations; however, this analysis does

not attempt to quantify potential macroeconomic consequences that

may be associated with mitigation.



5.2 Significant reductions in net greenhouse gas emissions are

technically possible and can be economically feasible. These reductions

can be achieved by utilizing an extensive array of technologies

and policy measures that accelerate technology development, diffusion,

and transfer in all sectors, including the energy, industry, transportation,

residential/commercial and agricultural/forestry sectors.



5.3 The degree to which technical potential and cost-effectiveness

are realized is dependent on initiatives to counter lack of information

and overcome cultural, institutional, legal, financial and economic

barriers which can hinder diffusion of technology or behavioural

changes.



5.4 By the year 2100, the world's commercial energy system in

effect will be replaced at least twice, offering opportunities

to change the energy system without premature retirement of capital

stock; significant amounts of capital stock in the industrial,

commercial, residential, and agricultural/forestry sectors will

also be replaced. These cycles of capital replacement provide

opportunities to utilize new, better performing technologies.



Energy Demand



5.5 The IPCC projects (IPCC 1992; IPCC 1994) that without policy

intervention, there could be significant growth in emissions from

the industrial, transportation, and commercial/residential buildings

sectors. Numerous studies have indicated that 10-30% energy efficiency

gains above present levels are feasible at negative to zero cost

in each of the sectors in many parts of the world through technical

conservation measures and improved management practices over the

next 2 to 3 decades. Using technologies that presently yield the

highest output of energy services for a given input of energy,

efficiency gains of 50-60% would be technically feasible in many

countries over the same time period. Achieving these potentials

will depend on future cost reductions, the rate of development

and implementation of new technologies, financing and technology

transfer, as well as measures to overcome a variety of non-technical

barriers. Because energy use is growing world-wide, even replacing

current technology with more-efficient technology could still

lead to an absolute increase in greenhouse gas emissions in the

future. Technologies and measures to reduce greenhouse gas emissions

in energy end-use sectors include:



* Industry: improving efficiency; recycling materials and switching

to those with lower greenhouse gas emissions; and developing processes

that use less energy and materials.

* Transportation: the use of very efficient vehicle drive-trains,

light-weight construction and low-air-resistance design; the use

of smaller vehicles; altered land-use patterns, transport systems,

mobility patterns and lifestyles; and shifting to less energy-intensive

transport modes; and the use of alternative fuels and electricity

from renewable and other fuel sources which do not enhance atmospheric

greenhouse gas concentrations.

* Commercial/residential: reduced heat transfers through building

structures and more-efficient space-conditioning and water supply

systems, lighting, and appliances.



Energy Supply



5.6 It is technically possible to realize deep emissions reductions

in the energy supply sector within 50 to 100 years using alternative

strategies, in step with the normal timing of investments to replace

infrastructure and equipment as it wears out or becomes obsolete.

Promising approaches, not ordered according to priority, include:



a. Greenhouse gas reductions in the use of fossil fuels



* More-efficient conversion of fossil fuels (e.g., combined heat

and power production and more efficient generation of electricity);



* Switching to low-carbon fossil fuels and suppressing emissions

(switching from coal to oil or natural gas, and from oil to natural

gas);

* Decarbonization of flue gases and fuels and carbon dioxide storage

(e.g., removal and storage of CO2 from the use of fossil fuel

feedstocks to make hydrogen-rich fuels);

* Reducing fugitive emissions, especially of methane, in fuel

extraction and distribution.



b. Switching to non-fossil fuel sources of energy



* Switching to nuclear energy (if generally acceptable responses

can be found to concerns such as about reactor safety, radioactive-waste

transport and disposal, and nuclear proliferation);

* Switching to renewable sources of energy (e.g., solar, biomass,

wind, hydro, and geothermal).



Integration of Energy System Mitigation Options



5.7 The potential for greenhouse gas emission reductions exceeds

the potential for energy use efficiency because of the possibility

of switching fuels and energy sources, and reducing the demand

for energy services. Even greater energy efficiency, and hence

reduced greenhouse gas emissions, could be attained with comprehensive

energy source-to-service chains.



5.8 To assess the potential impact of combinations of individual

measures at the energy systems level, "thought experiments"

exploring variants of a low-CO2 emitting energy supply system

were described. These variants illustrate the technical

possibility of deep reductions in CO2 emissions from the energy

supply system within 50 to 100 years using alternative strategies.

These exercises indicate the technical possibility of reducing

annual global emissions from 6 GtC in 1990 to about 4 GtC in 2050

and to about 2 GtC by 2100, ranging from about 450 GtC to about

470 GtC in these constructions, thus keeping atmospheric concentrations

below 500 ppmv.



5.9 Costs for integrated energy services relative to costs for

conventional energy depend on relative future energy prices, which

are uncertain within a wide range, and on the performance and

cost characteristics assumed for alternative technologies. However,

within the wide range of future energy prices, one or more of

the variants would plausibly be capable of providing the demanded

energy services at estimated costs that are approximately the

same as estimated future costs for current conventional energy.

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 and technological opportunities that are

imperfectly known, and on actions by governments and the private

sector. Improving energy efficiency, and a strong and sustained

investment in research, development, and demonstration to encourage

transfer and diffusion of alternative energy supply technologies

and improvements in energy efficiency is critical to deep reductions

in greenhouse gas emissions. Many of the technologies being developed

would need initial support to enter the market, and to reach sufficient

volume to lower costs to become competitive.



5.10 Market penetration and continued acceptability of different

energy technologies ultimately depends on their relative cost,

performance (including environmental performance), institutional

arrangements, and regulations and policies. Because costs vary

by location and application, the wide variety of circumstances

creates initial opportunities for new technologies to enter the

market. Deeper understanding of the opportunities for emissions

reductions would require more detailed analysis of options, taking

into account local conditions.



Industrial Process and Human Settlement Emissions



5.11 Large reductions are possible in process-related greenhouse

gases including CO2, CH4, N2O, halocarbons and SF6 in some cases;

and for capturing and utilizing methane from landfills and sewage

treatment facilities, and lowering the leakage rate of halocarbon

refrigerants from mobile and stationary sources (language to be

corrected).



Agriculture, Rangelands, and Forestry



5.12 Beyond the use of biomass fuels to displace fossil fuels,

the management of forests, agricultural lands, and rangelands

can play an important role in reducing current emissions of carbon

dioxide, methane, and nitrous oxide and enhancing carbon sinks.

A number of measures could conserve and sequester substantial

amounts of carbon (approximately 60-90 GtC in the forestry sector

alone) over the next 50 years. In the forestry sector, measures

include sustaining existing forest cover; slowing deforestation;

natural forest regeneration; establishment of tree plantations;

promoting agroforestry. Other practices in the agriculture sector

could reduce emissions of other greenhouse gases such as methane

and nitrous oxide. In the forestry sector, costs for conserving

and sequestering carbon in biomass and soil are estimated to range

widely but can be competitive with other mitigation options.



Policy Instruments



5.13 The availability of low carbon technologies is a prerequisite

for, but not a guarantee of, the ability to reduce greenhouse

gas emissions at reasonable cost. Mitigation of emissions depends

on reducing barriers to the diffusion and transfer of technology,

mobilizing financial resources, supporting capacity building in

developing countries and countries with economies in transition,

and other approaches to assist in the implementation of behavioural

changes and technological opportunities in all regions of the

globe. The optimum mix of policies will vary from country to country,

depending upon their energy markets, economic considerations,

political structure and societal receptiveness. The leadership

of national governments in applying these policies will contribute

to responding to the adverse consequences of climate change. Policies

to reduce net greenhouse gas emissions appear more easily implemented

when they are designed to also address other concerns that impede

sustainable development (e.g., air pollution, soil erosion). A

number of policies, many of which might be used by individual

nations unilaterally, and some of which may be used by groups

of countries and would require regional or international agreement,

can facilitate the penetration of less greenhouse gas-intensive

technologies and modified consumption patterns. These include,

inter alia (not ordered according to priority):



* Putting in place appropriate institutional and structural frameworks;



* Energy pricing strategies - for example, carbon or energy taxes,

and reduced energy subsidies;

* Phasing out those existing distortionary policies which increase

greenhouse gas emissions, such as some subsidies and regulations,

non-internalization of environmental costs, and distortions in

agriculture and transport pricing;

* Tradable emissions permits;

* Voluntary programs and negotiated agreements with industry;



* Utility demand-side management programs;

* Regulatory programs including minimum energy-efficiency standards,

such as for appliances and fuel economy;

* Stimulating research, development and demonstration to make

new technologies available;

* Market pull and demonstration programs that stimulate the development

and application of advanced technologies;

* Renewable energy incentives during market build-up;

* Incentives such as provisions for accelerated depreciation and

reduced costs for consumers;

* Education and training; information and advisory measures;

* Options that also support other economic and environmental goals.



The choice of measures at the domestic level may reflect objectives

other than cost-effectiveness such as meeting fiscal targets.

If a carbon or carbon-energy tax is used as a policy instrument

for reducing emissions, the taxes could raise substantial revenues

and how the revenues are distributed could dramatically affect

the cost of mitigation. If the revenues are distributed by reducing

distortionary taxes in the existing system, they will help reduce

the excess burden of the existing tax system, potentially yielding

an additional economic benefit (double dividend). For example,

those of the European studies which are more optimistic regarding

the potential for tax recycling, show lower and, in some instances,

slightly negative costs. Conversely, inefficient recycling of

the tax revenues could increase costs. For example, if the tax

revenues are used to finance government programs that yield a

lower return than the private sector investments foregone because

of the tax, then overall costs will increase. The choice of instruments

may also reflect other environmental objectives such as reducing

non-greenhouse pollution emissions or increasing forest cover

or other concerns such as specific impacts on particular regions

or communities.



6. EQUITY AND SOCIAL CONSIDERATIONS 




6.1 Equity considerations are an important aspect of climate change

policy and of the Convention and in achieving sustainable development.

Equity involves procedural as well as consequential issues. Procedural

issues relate to how decisions are made while consequential issues

relate to outcomes. To be effective and to promote cooperation,

agreements must be regarded as legitimate, and equity is an important

element in gaining legitimacy.



6.2 Procedural equity encompasses process and participation issues.

It requires that all Parties be able to participate effectively

in international negotiations related to climate change. Appropriate

measures to enable developing country Parties to participate effectively

in negotiations increase the prospects for achieving effective,

lasting, and equitable agreements on how best to address the threat

of climate change. Concern about equity and social impacts points

the need to build endogenous capabilities and strengthen institutional

capacities, particularly in developing countries, to make and

implement collective decisions in a legitimate and equitable manner.



6.3 Consequential equity has two components: the distribution

of the costs of damages or adaptation and of measures to mitigate

climate change. Because countries differ substantially in vulnerability,

wealth, capacity, resource endowments, and other factors listed

below, unless addressed explicitly, the costs of the damages,

adaptation, and mitigation may be borne inequitably.



6.4 Climate change is likely to impose costs on future generations

and on regions where damages occur, including regions with low

greenhouse gas emissions. Climate change impacts will be distributed

unevenly.



6.5 The intertemporal aspects of climate change policy also raise

questions of intergenerational equity because future generations

are not able to influence directly the policies being chosen today

that could affect their wellbeing, and because it might not be

possible to compensate future generations for consequent reductions

in their well-being. Discounting is the principal analytical tool

economists use to compare economic effects that occur at different

points in time. The choice of discount rate is of crucial technical

importance for analyses of climate change policy, because the

time horizon is extremely long, and mitigation costs tend to come

much earlier than the benefits of avoided damages. The higher

the discount rate, the less future benefits and the more current

costs matter in the analysis.



6.6 The Convention recognizes in Article 3.1 the principle of

common but differentiated responsibilities and respective capabilities.

Actions beyond "no regrets" measures impose costs on

the present generation. Mitigation policies unavoidably raise

issues about how to share the costs. The initial emission limitation

intentions of Annex I Parties represent an agreed collective first

step of those parties in addressing climate change.



6.7 Equity arguments can support a variety of proposals to distribute

mitigation costs. Most of them seem to cluster around or combine

approaches: equal per capita emission allocations and allocations

based on incremental departures from national baseline emissions

(current or projected). The implications of climate change for

developing countries are different from those for developed countries.

The former often have different urgent priorities, weaker institutions,

and are generally more vulnerable to climate change. However,

it is likely that developing countries' share of emissions will

grow further to meet their social and developmental needs. Greenhouse

gas emissions are likely to become increasingly global, even whilst

substantial per-capita disparities are likely to remain.



6.8 There are substantial variations both among developed and

developing countries that are relevant to the application of equity

principles to mitigation. These include variations in historical

and cumulative emissions, current total and per-capita emissions,

emission intensities and economic output, projections of future

emissions and factors such as wealth, energy structures, and resource

endowments.



A variety of ethical principles, including the importance

of meeting people's basic needs, may be relevant to addressing

climate change, but the application of principles developed to

guide individual behaviour to relations among states is complex

and not straightforward. Climate change policies should not aggravate

existing disparities between one region and another nor attempt

to redress all equity issues.



7. ECONOMIC DEVELOPMENT TO PROCEED IN A SUSTAINABLE MANNER



7.1 Economic development, social development and environmental

protection are interdependent and mutually reinforcing components

of sustainable development, which is the framework for our efforts

to achieve a higher quality of life for all people. The UNFCCC

notes that responses to climate change should be coordinated with

social and economic development in an integrated manner with a

view to avoiding adverse impacts on the latter, taking into full

account the legitimate priority needs of developing countries

for the achievement of sustainable development and the eradication

of poverty. The Convention also notes the common but differentiated

responsibilities and respective capabilities of all Parties to

protect the climate system. This section reviews briefly what

is known about the costs and benefits of mitigation and adaptation

measures as they relate, inter alia, to the sustainability of

economic development and environment.



Social Costs of Climate Change



7.2 Net climate change damages include both market and non-market

impacts as far as they can be quantified at present and, in some

cases, adaptation costs. Damages are expressed in net terms to

account for the fact that there are some beneficial impacts of

climate change as well, which are, however, dominated by the damage

costs. Non-market impacts, such as human health, risk of human

mortality and damage to ecosystems, form an important component

of available estimates of the social costs of climate change.

The estimates of non-market damages, however, are highly speculative

and not comprehensive and are thus a source of major uncertainty

in assessing the implications of global climate change for human

welfare.



7.3 The assessed literature quantifying total damages from 2 to

3°C warming provides a wide range of point estimates for

damages given the presumed change in atmospheric greenhouse gas

concentrations. The aggregate estimates tend to be a few percent

of world GDP, with, in general, considerably higher estimates

of damage to developing countries as a share of their GDP. The

aggregate estimates are subject to considerable uncertainty, but

the range of uncertainty cannot be gauged from the literature.

The range of estimates cannot be interpreted as a confidence interval

given the widely differing assumptions and methodologies in the

studies. Aggregation is likely to mask even greater uncertainties

about damage components. Regional or sectoral approaches to estimating

the consequences of climate change include a much wider range

of estimates of the net economic effects. For some areas, damages

are estimated to be significantly greater and could negatively

affect economic development. For others, climate change is estimated

to increase economic production and present opportunities for

economic development. Equalizing the value of a statistical life

at the level typical of that in developed countries would increase

monetized damages several times, and would further increase the

share of the developing countries in the total damage estimate.

Small islands and low lying coastal areas are particularly vulnerable.

Damages from possible large-scale catastrophes, such as major

changes in ocean circulation, are not reflected in these estimates.



Benefits of Limiting Climate Change



7.4 The benefits of limiting greenhouse gas emissions and enhancing

sinks are (a) the climate change damages and adaptation costs

avoided and (b) the indirect economic and environmental benefits

associated with the relevant policies - such as reductions in

other pollutants jointly produced with greenhouse gases, biological

diversity conserved and technological innovation driven by climate

change response.



Adaptation Costs



7.5 Many options are available for adapting to the impacts of

climate change and thus reducing the damages to national economies

and natural ecosystems. Adaptive options are available in many

sectors, ranging from agriculture and energy to health, coastal

zone management, off-shore fisheries and recreation. Some of these

provide enhanced ability to cope with the current impacts of climate

variability. Systematic estimates of the costs of adaptation to

cope with impacts on agriculture, human health, water supplies,

and other changes are not available. Where adaptation measures

are technically feasible, costs of adaptation, for example to

sea level rise, could be prohibitively expensive for some countries

without external assistance



Mitigation Costs and Benefits



7.6 The costs of stabilizing atmospheric concentrations of greenhouse

gases at levels and within a time frame which will prevent dangerous

anthropogenic interference with the climate system will be critically

dependent on the choice of emissions time path, consumption patterns,

resource and technology availability and the choice of policy

instruments. The cost of the abatement programme will be influenced

by the rate of capital replacement, the discount rate and the

effect of research and development. Failure to adopt policies

as early as possible to encourage efficient replacement investments

at the end of the economic life of plant and equipment (i.e.,

at the point of capital stock turnover) impose an economic cost

to society. Implementing emissions reductions at rates that can

be absorbed in the course of normal stock turnover are likely

to be cheaper than enforcing premature retirement now. The choice

of abatement paths thus involves balancing the economic risks

of rapid abatement now against the risks of delay. Mitigation

measures undertaken in a way that capitalize on other environmental

benefits could be cost-effective and enhance sustainable development.

Movement of polluting activities which lead to an increase in

global greenhouse gas emissions can be lessened through coordinated

actions of groups of countries.



7.7 While very few studies of the costs to stabilize atmospheric

concentrations of greenhouse gases have been published, some estimates

of the costs of various degrees of emissions reductions are available

in the literature. Mitigation cost estimates vary widely, depending

upon choice of methodologies, underlying assumptions, emission

scenarios, policy instruments, reporting year, etc.



7.8 Despite significant differences in views, there is agreement

that energy efficiency gains of perhaps 10% to 30% above baseline

trends over the next two to three decades can be realized at negative

to zero net cost. With longer time horizons, which allow a more

complete turnover of capital stocks and which give research, development

and demonstration, and market transformation policies a chance

to impact multiple replacement cycles, this potential is much

higher. The magnitude of such "no regrets" potential

depends upon the existence of substantial market or institutional

imperfections that prevent cost-effective emission reduction measures

from occurring. The key question is then the extent to which such

imperfections and barriers can be removed cost-effectively by

policy initiatives.



7.9 OECD countries: Although it is difficult to generalize,

top-down analyses suggest that the costs of substantial reductions

below 1990 CO2 emissions levels could be as high as several percent

of GDP. In the specific case of stabilizing emissions at 1990

levels, most studies estimate that annual costs in the range of

minus 0.5 percent of GDP (equivalent to a gain of about $60 billion

in total for OECD countries at today's GDP levels) to plus 2 percent

of GDP (equivalent to a loss of about $240 billion) could be reached

over the next several decades. However, studies also show that

appropriate timing of abatement measures and the availability

of low-cost alternatives may substantially reduce the size of

the overall bill. Some bottom-up studies show that the costs of

reducing emissions by 20% in developed countries within two to

three decades are negligible to negative. Other bottom-up studies

suggest that there exists a potential for absolute reductions

in excess of 50 % in the longer term, without increasing and perhaps

even reducing total energy system costs.



7.10 Countries with economies in transition: The potential

for cost-effective reductions in energy use is apt to be considerable

but the realizable potential will depend upon what economic and

technological development path is chosen, as well as the availability

of capital to pursue different paths. A critical issue is the

future of structural changes in these countries that are apt to

change dramatically the level of baseline emissions and the emission

reduction costs.



7.11 Developing countries: Analyses suggest that there

may be substantial low-cost fossil fuel carbon dioxide emission

reduction opportunities for developing countries. Development

pathways that increase energy efficiency, promote alternative

energy technologies, reduce deforestation and enhance agricultural

productivity and biomass energy production can be economically

beneficial. To embark upon this pathway may require significant

international cooperation and financial and technology transfer.

However, these are likely to be insufficient to offset rapidly

increasing emissions baselines, associated with increased economic

growth and overall welfare. Stabilization of carbon dioxide emissions

is likely to be costly.



7.12 Cost estimates for a number of specific approaches to mitigating

emissions or enhancing sinks of greenhouse gases vary widely and

depend on site-specific characteristics. This is true for renewable

energy technologies, for example, as well as carbon sequestration

options. The latter could offset as much as 15-30% of 1990 global

energy-related emissions each year in forests for the next 50

years. The costs of carbon sequestration, which are competitive

with source control options, differ among regions of the world.

About 10% of anthropogenic methane emissions could be reduced

at negative or low cost using available mitigation options for

such methane sources as natural gas systems, waste management,

and agriculture.



7.13 Control of emissions of other greenhouse gases, especially

methane and nitrous oxide, can provide significant cost-effective

opportunities in some countries. Costs differ between countries

and regions for some of these options.



Subsidies, Market Imperfections and Barriers



7.14 The world economy and indeed some individual national economies

suffer from a number of price distortions which increase greenhouse

gas emissions, such as some agricultural and fuel subsidies and

distortions in transport pricing. A number of studies of this

issue indicate that global emissions reductions of 4 to 18 % together

with increases in real incomes are possible from phasing out fuel

subsidies.



7.15 Progress has been made in a number of countries in cost-effectively

reducing imperfections and institutional barriers in markets through

policy instruments based on voluntary agreements, energy efficiency

incentives, product efficiency standards and energy efficiency

procurement programs involving manufacturers, and utility regulatory

reforms. Where empirical evaluations have been made, many have

found that the benefit-cost ratio of increasing energy efficiency

was favourable, suggesting the practical feasibility of realizing

"no regrets" potentials at negative net cost.



Value of Better Information and Research



The value of better information about the processes, impacts

of and responses to climate change is likely to be great. Analysis

of economic and social issues related to climate change, especially

in developing countries, is a high priority for research. Further

analysis is required concerning effects of response options on

employment, inflation, trade, competitiveness and other public

issues.



8. THE ROAD FORWARD 



8.1 The scientific, technical, economic and social science literature

does suggest ways to move forward towards the ultimate objective

of the Convention. Possible actions include mitigation of climate

change through reductions of emissions of greenhouse gases and

enhancement of their removal by sinks, adaptation to observed

and/or anticipated climate change, and research, development and

demonstration to improve our knowledge of the risks of climate

change and possible responses.



8.2 Uncertainties remain which are relevant to judgement of what

constitutes dangerous anthropogenic interference with the climate

system and what needs to be done to prevent such interference.

The literature indicates, however, that significant "no regrets"

opportunities are available in most countries and that the risk

of aggregate net damage due to climate change, consideration of

risk aversion and the precautionary approach, provide rationales

for actions beyond "no regrets". The challenge is not

to find the best policy today for the next 100 years, but to select

a prudent strategy and to adjust it over time in the light of

new information.



8.3 The literature suggests that flexible, cost-effective policies

relying on economic incentives and instruments as well as coordinated

instruments, can considerably reduce mitigation or adaptation

costs, or can increase the cost-effectiveness of emission reduction

measures. Appropriate long-run signals are required to allow producers

and consumers to adapt cost-effectively to constraints on greenhouse

gas emissions and to encourage investment, research, development

and demonstration.



8.4 Many of the policies and decisions to reduce emissions of

greenhouse gases and enhance their sinks, and eventually stabilize

their atmospheric concentration, would provide opportunities and

challenges for the private and public sectors. A carefully selected

portfolio of national and international responses of actions aimed

at mitigation, adaptation and improvement of knowledge can reduce

the risks posed by climate change to ecosystems, food security,

water resources, human health and other natural and socio-economic

systems. There are large differences in the cost of reducing greenhouse

gas emissions, and enhancing sinks, among countries due to their

state of economic development, infrastructure choices, and natural

resource base. International cooperation in a framework of bilateral,

regional or international agreements could significantly reduce

the global costs of reducing emissions and lessening emission

leakages. If carried out with care, these responses would help

to meet the challenge of climate change and enhance the prospects

for sustainable economic development for all peoples and nations.



DRAFTING TEAM FOR THE SYNTHESIS



1. Bert Bolin (Chairman of the IPCC and Chairman of the Drafting Team)

2. John T. Houghton 

3. Gylvan Meira Filho

4. Robert T. Watson

5. M. C. Zinyowera

6. James Bruce

7. Hoesung Lee

8. Bruce Callander

9. Richard Moss

10 Erik Haites

11. Roberto Acosta Moreno

12. Tariq Banuri

13. Zhou Dadi

14. Bronson Gardner

15. José Goldemberg

16. Jean-Charles Hourcade

17. Michael Jefferson

18. Jerry Melillo

19. Irving Mintzer

20. Richard Odingo

21. Martin Parry

22. Martha Perdomo

23. Cornelia Quennet-Thielen

24. Pier Vellinga

25. Narasimhan Sundararaman (Secretary of the IPCC)



REFERENCES



1. IPCC, 1990: (i) Cimate Change, The IPCC Scientific Assessment



(ii) Climate Change, The IPCC Impacts Asessment

(iii) Climate Change, The IPCC Response Strategies

(iv) Overview and Policymakers Summary



2. IPCC, 1992: (i) Climate Change 1992, The Supplementary Report

to the IPCC Scientific Assessment

(ii) Climate Change 1992, The Supplementary Report to the IPCC

Impacts Assessment



3. IPCC, 1994: Climate Change 1994, Radiative Forcing of Climate

Change and an Evaluation of the IPCC IS92 Emission Scenarios



4. IPCC, 1995: (i) Climate Change 1995, The IPCC Synthesis



(ii) Climate Change 1995, The Science of Climate Change

(iii) Climate Change 1995, Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change

(iv) Climate Change 1995, The Economic and Social Dimensions of Climate Change