United Nations Environment Programme (UNEP)
Global  Environment Outlook-1 - The Web version

Chapter 4: Looking to the Future

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Climate Change and Acidification

Projected Trends

[ Climate Change | Acidification ]

Energy demands are projected to grow significantly both globally and across all regions (Raskin and Margolis, 1995). In particular, economic development in industrializing countries will require a spectacular increase in energy consumption. For Africa, West Asia/Middle East, and Asia, this increase is assumed to be by a factor of five or more by the year 2050, despite the assumption that energy intensity will decline in all regions. The increased energy demand is expected to continue to be met primarily by fossil fuels. Figure 4.5 shows key aspects of the energy scenario, which assumes that development is not constrained by limited availability of energy resources. Various estimates of future sulphur dioxide emissions for selected countries or regions are reported in the literature. (See Table 4.3a.) For the purpose of this analysis, the global emission estimates given in Posch et al.(1996) were applied. (See also Table 4.3b.)

Two different levels of sulphur dioxide emissions have been assumed: uncontrolled growth and partial controls (agreed-upon emission reductions in OECD countries and for most other countries a linear reduction of emission factors to about 50 per cent in 2050). No additional emission controls have been assumed beyond those already agreed on internationally.

The analysis does not necessarily include all the latest and planned national-level policies. At the global level, the growth in developing countries' economies outweighs the decrease or stabilization of carbon dioxide emissions in industrial countries. Not only do global carbon dioxide emissions continue to move upwards, but the declining trend in emissions of sulphur and nitrogen compounds will also be reversed.

Climate Change Trends

Most impact assessments of climate change to date have centred on industrial countries at medium and high latitudes. This is partly because most computer models project that the largest temperature changes are likely to occur at these latitudes, and partly because ecosystems at these latitudes are often particularly vulnerable to climatic changes. Nevertheless, the models also indicate that developing countries in low latitudes may experience important changes in climate as well, including crucial revisions in rainfall patterns (IPCC, 1990, 1996). Moreover, developing countries may be more vulnerable in other respects (e.g., agriculture or housing) because their less developed economies and infrastructures impede adaptation to new climate patterns. Recently completed studies indicate the special vulnerability of developing countries to impacts such as more frequent droughts and coastal flooding (IPCC, 1996).

Although overall global food production may not be harmed by projected climatic changes, according to IPCC (1996) there will be large regional differences. (See also "Use of Land" below.) Figure 4.7 provides an example of one possible impact of climate change on food production between 1990 and 2050. It indicates the major current areas of maize cultivation that are projected to experience higher or lower yields as a result of changes in temperature and precipitation.

In some areas, production may rise, but in other vulnerable areas, negative impacts may occur. These risks are particularly important for developing countries in semi-arid zones because they are less able to adapt to change than industrial countries are. Food imports from less affected regions may be an important mechanism for dealing with the impacts of climate change on crop yields. The analyses here highlight the fact that it is important to focus on regional "redistribution" of climate (with the associated changes in agricultural productivity and trade patterns) as well as on globally averaged climatic changes.

Acidification Trends

Integrated assessment models have been used for the areas most affected to date Europe (Amann et al.,1995) and Asia (Foell et al.,1995a and 1995b; Morita et al.,1995). For this chapter, atmospheric models have been used to estimate how winds will transport and redistribute acidifying pollutants throughout Asia (Arndt and Carmichael, 1995) and Europe (Barrett and Seland, 1995). This information has been combined with estimates of the deposition levels that are considered acceptable (critical loads) for local ecosystems (Downing et al., 1993; Hettelingh et al.,1991 and 1995a; Posch et al., 1995). Based on sulphur dioxide emissions shown in Table 4.3b, the results of this simulation indicate that, even under partial controls, substantive risks of acidification exist in Asia.

A comparison with other modelling studies, such as the Asian-Pacific Integrated Model of Morita et al.(1995), finds comparable results for the Asia region. Woodlands in some developing areas could deteriorate rapidly, endangering supplies of fuelwood and other products. In some areas acid deposition will lead to the release of toxic metals to ground and surface water, further contaminating drinking water supplies. Agricultural crops become increasingly subject to risk because of the excess of critical loads in soils and high sulphur dioxide concentrations in the air (exceeding critical levels), resulting in lower cereal yields.

Unlike the situation with climate change, reductions in emissions of acidifying gases lead relatively quickly to lower deposition levels, followed after some time by rehabilitation of the ecosystems affected (typically this would take one to five decades, provided that biogeochemical balances were not distorted too much when the depositions took place). Taking into account the impact of the implementation of international treaties on acidification as well as future trends in energy use and the economy in Europe, it has been estimated that the ecosystem area affected by sulphur-based acid deposition in Europe may decrease from 19 per cent in 1990 to 10 per cent in 2010 (Hettelingh et al., 1995a).

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