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possibility of a different future climate, especially with regard to water resources. At least, we must get ready for a future more uncertain than that suggested by past records.

Most of our present scientific perspective on climate change has been around for more than a decade, and the first scientific discussions of the possible effect on climate of increasing carbon dioxide concentrations date back more than a century. Half a dozen or more assessments of the current scientific consensus have been conducted since 1979, authored by prestigious National Research Council committees and international workshops. It is really striking how little divergence there has been in the conclusions of these studies.

The latest assessment by the scientific community of climate change, just now being released, was carried out by hundreds of scientists and was orchestrated by an organization established just for this task: the Working Group Number One of the Intergovernmental Panel for Climate Change (IPCC) (IPCC, 1990). The IPCC report addresses four topics related to climate change:

  1. factors that may affect climate change during the next century, especially those related to human activity;

  2. responses of the atmosphere-ocean-land-ice system to climate change;

  3. current capabilities for modeling global and regional climate changes; and

  4. the past climate record and presently observed climate anomalies.

The IPCC report looks especially at the following questions:

  • What factors determine global climate?

  • What are the greenhouse gases, and how and why are their concentrations increasing?

  • Which greenhouse gases are the most important in climate change?

  • How much do we expect the climate to change?

  • How much confidence do we have in our predictions?

  • Will the climate of the future be very different from today's climate?

  • Have human activities already begun to change the global climate?

  • How much will the sea level rise if the climate changes?

  • How will climate change affect ecosystems?

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