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1.1 Following a resolution of the Executive Council of the Convention on Climate Change (UNFCCC) which was open for World Meteorological Organization (July 1992), the IPCC decided signature at the Earth Summit in Rio in 1992. to include an examination of approaches to Article 2, the Objective of the UN Framework Convention on Climate Change (UNFCCC), 1.4 The ultimate objective of the UNFCCC, as expressed in in its work programme. It organized a workshop on the subject in Article 2 is: October 1994 in Fortaleza, Brazil, at the invitation of the Government of Brazil. Thereafter, the IPCC Chairman assembled a ... stabilization of greenhouse gas concentrations in the atmosphere at team of lead authors (listed at the end of this report in the a level that would prevent dangerous anthropogenic interference with Appendix) under his chairmanship to draft the Synthesis. The team the climate system. Such a level should be achieved within a timeproduced the draft which was submitted for expert and government frame sufficient to allow ecosystems to adapt naturally to climate review and comment. The final draft Synthesis was approved line by change, to ensure that food production is not threatened and to enable line by the IPCC at its eleventh session (Rome, 11-15 December economic development to proceed in a sustainable manner'. 1995), where representatives of 116 governments were present as well as 13 intergovernmental and 25 non-governmental organiza- 1.5

The challenges presented to the policymaker by Article 2 tions. It may be noted for information that all Member States of the are the determination of what concentrations of greenhouse gases World Meteorological Organization and of the United Nations are might be regarded as “dangerous anthropogenic interference with Members of the IPCC and can attend its sessions and those of its the climate system and the charting of a future which allows for Working Groups. The Synthesis presents information on the scien. economic development which is sustainable. The purpose of this tific and technical issues related to interpreting Article 2 of the synthesis report is to provide scientific, technical and socioUNFCCC, drawing on the underlying IPCC Second Assessment economic information that can be used, inter alia, in addressing Report. Since the Synthesis is not simply a summary of the IPCC these challenges. It is based on the 1994 and 1995 reports of the Second Assessment Report, the Summaries for Policymakers of the IPCC Working Groups. three IPCC Working Groups should also be consulted for a summary of the Second Assessment Report.

1.6 The report follows through the various matters which are

addressed in Article 2. It first briefly summarizes the degree of 1.2 During the past few decades, two important factors climate change the "interference with the climate system" regarding the relationship between humans and the Earth's climate which is projected to occur as a result of human activities. It then have become apparent. First, human activities, including the goes on to highlight what we know about the vulnerabilities of burning of fossil fuels, land-use change and agriculture, are increas- ecosystems and human communities to likely climate changes, ing the atmospheric concentrations of greenhouse gases (which especially in regard to agriculture and food production and to other tend to warm the atmosphere) and, in some regions, aerosols factors such as water availability, health and the impact of sea-level (microscopic airborne particles, which tend to cool the atmos- rise which are important considerations for sustainable develop phere). These changes in greenhouse gases and aerosols, taken ment. The task of She IPCC is to provide a sound scientific basis that together, are projected to change regional and global climate and would enable policymakers to better interpret dangerous anthro climate-related parameters such as temperature, precipitation, soil pogenic interference with the climate system. moisture and sea level. Second, some human communities have become more vulnerable to hazards such as storms, floods and 1.7 Given current trends of increasing emissions of most droughts as a result of increasing population density in sensitive greenhouse gases, atmospheric concentrations of these gases will areas such as river basins and coastal plains. Potentially serious increase through the next century and beyond. With the growth in changes have been identified, including an increase in some regions atmospheric concentrations of greenhouse gases, interference with in the incidence of extreme high-temperature events, foods and the climate system will grow in magnitude and the likelihood of droughts, with resultant consequences for fires, pest outbreaks, and adverse impacts from climate change that could be judged dangerecosystem composition, structure and functioning, including ous will become greater. Therefore, possible pathways of future net primary productivity.

emissions were considered which might lead to stabilization at

different levels and the general constraints these imply. This 1.3 Scientific and technical assessments of climate change and its impacts have been conducted by the Intergovernmental Panel on

| Vulnerability defines the extent to which climate change may damage or Climate Change (IPCC). The First Assessment, published in 1990,

harm a system. It depends not only on a system's sensitivity but also on its provided a scientific and technical base for the UN Framework ability to adapt to new climatic conditions.


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.

report presents available scientific and technical information on these three choices. It also notes where uncertainties remain regarding such information. Article 3 of the UNFCCC 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 3.32 provides guidance, inter alia, on decision-making where there is a lack of full scientific certainty, namely that the Parties should:

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 "danger. ous anthropogenic interference with the climate system”.

"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."

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.

The Second Assessment Report of the IPCC also provides information in this regard.

1.11 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.

1.10 Decisions with respect to Article 2 of the UNFCCC involve three distinct but interrelated choices: stabilization level, net emissions pathway and mitigation technologies and policie The

2 Kuwait registered its objection to quoting only subparagraph 3 of Article 3 and not the Article in its entirety,



pogenic 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.


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


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 (CHA) and nitrous oxide (N2O), have grown significantly since pre-industrial times (about 1750 A.D.): CO2 from about 280 to almost 360 ppmv), CH, from 700 to 1720 ppbv and N O 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 anthro

ppmv stands for parts per million by volume; ppbv stands for parts per billion (thousand million) by volume. Values quoted are for 1992.



due to greenhouse gases. In contrast to the long-lived greenhouse sensitivity and including the effects of future changes in aerosol gases, anthropogenic aerosols are very short-lived in the atmosphere concentrations leads to a projected increase of about 1°C by 2100. and hence their radiative forcing adjusts rapidly to increases or The corresponding projection for the highest IPCC scenario (IS92e) decreases in emissions.

combined with a "high" value of climate sensitivity gives a warming

of about 3.5°C. In all cases the average rate of warming would prob Global mean surface temperature has increased by between ably be greater than any seen in the last 10,000 years, but the actual about 0.3 and 0.6°C since the late 19th century, a change that is annual to decadal changes would include considerable natural variunlikely to be entirely natural in origin. The balance of evidence, ability. Regional temperature changes could differ substantially from changes in global mean surface air temperature and from from the global mean value. Because of the thermal inertia of the changes in geographical, seasonal and vertical patterns of atmos- oceans, only 50-90% of the eventual equilibrium temperature pheric temperature, suggests a discernible human influence on global change would have been realized by 2100 and temperature would climate. There are uncertainties in key factors, including the magni- continue to increase beyond 2100, even if concentrations of greentude and patterns of long-term natural variability. Global sea level house gases were stabilized by that time. 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. 2.8 Average sea level is expected to rise as a result of thermal

expansion of the oceans and melting of glaciers and ice-sheets. For 2.5 There are inadequate data to determine whether consist. the 1592a scenario, assuming the "best estimate" values of climate ent global changes in climate variability or weather extremes have sensitivity and of ice melt sensitivity to warming, and including occurred over the 20th century. On regional scales there is clear the effects of future changes in aerosol concentrations, models evidence of changes in some extremes and climate variability indi- project an increase in sea level of about 50 cm from the present to cators. Some of these changes have been toward greater variability, 2100. This estimate is approximately 25% lower than the "best some have been toward lower variability. However, to date it has estimate" in 1990 due to the lower temperature projection, but not been possible to firmly establish a clear connection between also reflecting improvements in the climate and ice melt models. these regional changes and human activities.

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

climate and ice melt sensitivities and including aerosol effects Possible consequences of future interference

gives a projected sea-level rise of about 15 cm from the present to

2100. The corresponding projection for the highest emission 2.6 In the absence of mitigation policies or significant techno- scenario (1892e) combined with "high" climate and ice-melt logical advances that reduce emissions and/or enhance sinks, sensitivities gives a sea-level rise of about 95 cm from the present concentrations of greenhouse gases and aerosols are expected to grow to 2100. Sea level would continue to rise at a similar rate in future throughout the next century. The IPCC has developed a range of centuries beyond 2100, even if concentrations of greenhouse gases scenarios, 15922-f, of future greenhouse gas and aerosol precursor emis were stabilized by that time, and would continue to do so even sions based on assumptions concerning population and economic beyond the time of stabilization of global mean temperature. growth, land-use, technological changes, energy availability and fuel Regional sea-level changes may differ from the global mean value mix during the period 1990 to 21004. By the year 2100, carbon diox. owing to land movement and ocean current changes. ide 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 2.9 Confidence is higher in the hemispheric-to-continental scale as 36 GtC per year, with the lower end of the IPCC range assuming low projections of coupled atmosphere-ocean climate models than in the population and economic growth to 2100. Methane emissions are regional projections, where confidence remains low. There is more projected to be in the range 540 to 1170 Tg6CH, per year (1990 emis- confidence in temperature projections than hydrological changes. sions were about 500 Tg CH2); nitrous oxide emissions are projected to be in the range 14 to 19 Tg N per year (1990 emissions were about 2.10 All model simulations, whether they were forced with 13 Tg N). In all cases, the atmospheric concentrations of greenhouse increased concentrations of greenhouse gases and aerosols or with gases and total radiative forcing continue to increase throughout the increased concentrations of greenhouse gases alone, show the follow. simulation period of 1990 to 2100.

ing features: greater surface warming of the land than of the sea in

winter; a maximum surface warming in high northern 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 * See Table 1 in the Summary for Policymakers of IPCC Working Group II. project an increase in global mean surface temperature relative to

$ To convert GC (gigatonnes of carbon or thousand million tonnes of 1990 of about 2°C by 2100. This estimate is approximately one- carbon) to mass of carbon dioxide, multiply GoC by 3.67. third lower than the "best estimate" in 1990. This is due primarily 6 Tg: teragram is 1012 grams. to lower emission scenarios (particularly for CO2 and CFCs), the


In IPCC reports, climate sensitivity usually refers to long-term (equilib inclusion of the cooling effect of sulphate aerosols, and improve rium) change in global mean surface temperature following a doubling of ments in the treatment of the carbon cycle. Combining the lowest

atmospheric equivalent CO2 concentration. More generally, it refers to the

equilibrium change in surface air temperature following a unit change in IPCC emission scenario (1892c) with a "low" value of climate radiative forcing (*C/Wm2).



latitudes in winter, little surface warming over the Arctic in summer, 2.12 There are many uncertainties and many factors currently an enhanced global mean hydrological cycle, and increased precipi- limit our ability to project and detect future climate change. tation and soil moisture in high latitudes in winter. All these changes Future unexpected, large and rapid climate system changes are associated with identifiable physical mechanisms.

(as have occurred in the past) are, by their nature, difficult to

predict. This implies that future climate changes may also involve 2.11

Warmer temperatures will lead to a more vigorous 'surprises”. In particular, these arise from the non-linear nature hydrological cycle; this translates into prospects for more severe of the climate system. When rapidly forced, non-linear systems droughts and/or floods in some places and less severe droughts are especially subject to unexpected behaviour. Progress can and/or floods in other places. Several models indicate an increase in be made by investigating non-linear processes and subprecipitation intensity, suggesting a possibility for more extreme components of the climatic system. Examples of such non-linear rainfall events. Knowledge is currently insufficient to say whether behaviour include rapid circulation changes in the North there will be any changes in the occurrence or geographical Atlantic and feedbacks associated with terrestrial ecosystem distribution of severe storms, e.g., tropical cyclones.




3.1 This section provides scientific and technical information subject to multiple climatic and non-climatic stresses, the interacthat can be used, inter alia, in evaluating whether the projected tions of which are not always linear or additive, and very few studies range of plausible impacts constitutes "dangerous anthropogenic have considered dynamic responses to steadily increasing conceninterference with the climate system“, as referred to in Article 2, and trations of greenhouse gases or the consequences of increases in evaluating adaptation options. However, it is not yet possible to beyond a doubling of equivalent atmospheric CO2 concentrations, link particular impacts with specific atmospheric concentrations of greenhouse gases.

3.5 Unambiguous detection of climate-induced changes in

most ecological and social systems will prove extremely difficult in 3.2 Human health, terrestrial and aquatic ecological systems, the coming decades. This is because of the complexity of these and socio-economic systems (e.g., agriculture, forestry, fisheries and systems, their many non-linear feedbacks, and their sensitivity to a water resources) are all vital to human development and well-being large number of climatic and non-climatic factors, all of which are and are all sensitive to both the magnitude and the rate of climate expected to continue to change simultaneously. As future climate change. Whereas many regions are likely to experience the adverse extends beyond the boundaries of empirical knowledge (i.e., the effects of climate change some of which are potentially documented impacts of climate variation in the past), it becomes irreversible — some effects of climate change are likely to be more likely that actual outcomes will include surprises and beneficial. Hence, different segments of society can expect to unanticipated rapid changes. confront a variety of changes and the need to adapt to them.

Sensitivity of systems 3.3 Human-induced climate change represents an important additional stress, particularly to the many ecological and socio- Terrestrial and aquatic ecosystems economic systems already affected by pollution, increasing resource demands, and non-sustainable management practices. The 3.6 Ecosystems contain the Earth's entire reservoir of genetic vulnerability of human health and socio-economic systems and species diversity and provide many goods and services including to a lesser extent, ecological systems - depends upon economic (1) providing food, fibre, medicines and energy; (ii) processing and circumstances and institutional infrastructure. This implies that storing carbon and other nutrients; (ili) assimilating wastes, purifying systems typically are more vulnerable in developing countries where water, regulating water runoff, and controlling floods, soil degradaeconomic and institutional circumstances are less favourable. tion and beach erosion; and (lv) providing opportunities for

recreation and tourism. The composition and geographic distribu3.4 Although our knowledge has increased significantly tion of many ecosystems (e.g., forests, rangelands, deserts, mountain during the last decade and qualitative estimates can be developed, systems, lakes, wetlands and oceans) will shift as individual species quantitative projections of the impacts of climate change on any respond to changes in climate; there will likely be reductions in particular system at any particular location are difficult because biological diversity and in the goods and services that ecosystems regional-scale climate change projections are uncertain; our current provide society. Some ecological systems may not reach a new equiunderstanding of many critical processes is limited; systems are librium for several centuries after the climate achieves a new balance.

- and,

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