IPCC SECOND ASSESSMENT SYNTHESIS OF SCIENTIFIC-TECHNICAL INFORMATION RELEVANT This section illustrates the impact of climate change on a number of Anticipated hydrological changes and reductions in the areal extent selected ecological systems. 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. 3.7 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 lowlatitude boundaries of cold- and cool-water 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 3.12 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 nonlinear 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 increas ingly 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 sea-level rise would increase this number to about 92 million; a 1-meter sea-level rise would raise it to about 118 million. 3.11 CLIMATE CHANGE 1995: IPCC SECOND ASSESSMENT REPORT Studies using a 1-meter projection show a particular risk for small coexistent and interacting factors that characterize the vulnerability 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 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 lowlying 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. 3.18 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. ANALYTICAL APPROACH TO STABILIZATION OF ATMOSPHERIC CONCENTRATIONS OF GREENHOUSE GASES 4 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 IPCC SECOND ASSESSMENT SYNTHESIS OF SCIENTIFIC-TECHNICAL INFORMATION RELEVANT TO INTERPRETING ARTICLE 2 OF THE UN FRAMEWORK CONVENTION ON CLIMATE CHANGE Other greenhouse gases include tropospheric ozone (whose chemical precursors include nitrogen oxides, non-methane hydrocarbons and carbon monoxide), halocarbons (including HCFCs and HFCs) and SF. 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. 4.6 Carbon dioxide is removed from the atmosphere by a number of processes that operate on different time-scales. It has a relatively long residence time in the climate system of the order of a century or more. If net global anthropogenic emissions 10 (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 stabilization of the concentration of carbon dioxide at its present level could only be achieved through an immediate reduction in its emissions of 5070% 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 stabilized concentration is governed more by the accumulated anthropogenic carbon dioxide emissions from now until the time of stabilization, than by the way those emissions change over the period. This means that, for a given stabilized 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 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. 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!! 4.1112 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). 4.1213 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 9 Most halocarbons, but neither HFCs nor PFCs, are controlled by the Montreal Protocol and its Adjustments and Amendments. 10 For the remainder of Section 4, "net global anthropogenic emissions" (1.e., anthropogenic sources minus anthropogenic sinks) will be abbreviated to "emissions". 11 China registered its disagreement on the use of carbon dioxide emissions derived on the basis of a per unit economic activity. 12 The Panel agreed that this paragraph shall not prejudge the current nego tiations under the UNFCCC. 13 The Panel agreed that this paragraph shall not prejudge the current negotiations under the UNFCCC. CLIMATE CHANGE 1995: IPCC SECOND ASSESSMENT REPORT S 1000 S 750 S 650 $ 550 $ 450 2000 2050 2100 2150 2200 2250 2300 2350 Year Figure 1 (a). Carbon dioxide concentration profiles leading to stabilization 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 stabilizes at a carbon dioxide concentration of 1000 ppmv and follows IS92a emissions until at least the year 2000 has also been defined. Stabilization at concentrations of 450, 650 and 1000 ppmv would lead to equilibrium temperature increases relative to 199014 due to carbon dioxide alone (i.e., not including effects of other greenhouse gases (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. 600 550 500 450 400 350 20 1592a Current anthropogenic CO, emissions 2000 2050 2100 2150 2200 2250 2300 2350 Year 40 Figure 1 (b). Carbon dioxide emissions leading to stabilization 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. IPCC SECOND ASSESSMENT SYNTHESIS OF SCIENTIFIC-TECHNICAL INFORMATION RELEVANT Table 1. Total anthropogenic carbon dioxide emissions accumulated from 1991 to 2100 inclusive (GTC) for the IS92 scenarios (see Table 1 in the Summary for Policymakers of IPCC Working Group II) and for stabilization at various levels of carbon dioxide concentration following the two sets of pathways shown in Figure 1 (a). The accumulated emissions leading to stabilization 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. 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 |