CAMBRIDGE: This month the United States Government issued a path-breaking report on the impact of long-term climate change on America's society and environment. We know that human activity is causing serious and complex changes in the global climate, mainly through the effects of burning fossil fuels like oil and gas, and the effects of deforestation. These activities raise the level of carbon dioxide in the atmosphere, which in turn has many effects: a rise in average temperature, a rise in the water level of the oceans, significant changes in the global patterns of rainfall, and an increase in "extreme weather events" such as hurricanes and droughts. The new US study is the first systematic attempt to understand the long-term consequences of these climatic trends in a single country. It is a project of such significance and scope that it should quickly be followed up by similar studies in other parts of the world.
The new report, "Climate Change Impacts on the United States" (available on the website www.gcrio.org) is a remarkable accomplishment, even though it is really only one step in a long-term effort to understand the interactions of climate, environment, and human society. It was produced by a huge team of scientists working in different disciplines and different parts of the United States. If there is one main lesson, it is that long-term climate change is for real, and is likely to have major impacts on US society. If there is a second lesson, it is that those impacts are complex and varied, and depend very much on the characteristics of particular regions. What is good for one part of the country, or indeed one part of the world, might be a disaster for another.
The report stresses that climate change will have several interacting elements. The rise of carbon dioxide in the atmosphere B which is the main cause of the long-term climate change B might actually have some directly beneficial effects, since a higher concentration of carbon dioxide can stimulate the faster growth of some types of forests and some crops. On the other hand, the effects on temperature, rainfall, ocean levels, flooding and droughts, and other climate patterns, will hurt some regions, while even helping some others. Northern regions, for example, could enjoy a longer growing season for some crops, while more Southerly regions, which are already hot, might suffer from the adverse effects of rising temperatures.
A major novelty of the study is to analyze the impacts of climate change on several different regions of the US, and on several different sectors such as agriculture, health, water management, forestry, and coastal resources (many of which will be submerged or damaged by rising ocean levels and the increased severity of storms). There are strong hints of what might go right or wrong, but also clear warnings in the report that much more scientific work will be needed to get more accurate results. For example, the report relies on two different mathematical models of the atmosphere. These models point in similar directions about long-term trends, but they often give very different specific predictions. Also, little is known about how fast our societies will be able to adjust to the future changes if we can see them coming.
The problem of climate change is undoubtedly one of the toughest global issues to address. First, it is truly a global problem. One country can't protect itself by behaving well (for example using energy efficiently) if other countries are not taking similar actions. Second, it is a very huge problem, since the climatic changes in the coming decades are likely to be quite sizeable. Third, it is a very complicated problem. The scientific understanding of long-term climate change is still very limited, and even when it is understood, the effects of climate on society are complicated. And fourth, nations are likely to differ widely in their particular interests in this issue. Some countries are major contributors to the problem; others are major victims. Victims and perpetrators might not be the same.
It is now vital for other countries to carry out "national assessments" of the effects of long-term climate change, following the example of the US study. There is good scientific reason to believe that many tropical regions will experience vastly more damage from global warming than will temperate-zone countries like the US. For example, the effects of global warming on Africa and India could be very severe, even though their economies have contributed very little to the overall problem (since Africa and India use so little energy per person, they also contribute very little to the build up of atmospheric carbon dioxide). Some regions - especially in the tropics - might be big losers in this process, even though they themselves have done little to cause the problems.
Ironically, it is the poorest countries that have the least resources to carry out the needed analyses. Donor agencies such as the World Bank should therefore help to fund such studies. Unless these studies are done, poor countries might find themselves continuing victims of worsening climatic shocks, such as severe hurricanes, droughts, and flooding, without realizing that the events are not accidental, but the result of long-term patterns of global energy use. By understanding those linkages better, poor countries will have a much better idea of how to prepare for the likely climatic changes in the future, and how better to represent their own interests in the future negotiations over global responses to climate change. This, in turn, should help us to reach more realistic and sound global responses to this tremendous challenge.