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 coldrelated 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 nonvector-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 watermanagement 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. 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. 4. 4.1 ANALYTICAL APPROACH TO STABILIZATION OF ATMOSPHERIC 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 CH. 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 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. 4.4 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. Most halocarbons, but neither HFCs nor PFCs, are controlled by the Montreal Protocol and its 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. 10 For the remainder of Section 4. "net global anthropogenic emissions" (i.e. anthropogenic sources minus anthropogenic sinks) will be abbreviated to "emissions". Figure 1 (a) Carbon dioxide concentration profiles leading to stabilisation at 450, 550, 650 and 750 ppmv following the pathways defined in [PCC (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. 9 00 20 10 10 CO 2140 2190 2230 2340 Year 31000 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. 15920 15921 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). 15924 IS 924 These numbers do not take into account the increase in temperature (0.1 to 0.7 °C) which would 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. 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). |