It also states for the first time that the evidence is overwhelming that humans are causing most of the change. The report comes against a backdrop of international disagreement over how to curb rising levels of greenhouse gases in the atmosphere, largely carbon dioxide. The United States and Europe are at odds over details of the 1997 Kyoto Protocol, which provides guidelines for the reduction of greenhouse gases. Opponents of the treaty, which has not been approved by the U.S. Senate, argue that it hurts developed nations and would limit economic growth in the United States. Atmospheric carbon dioxide slows the rate at which heat radiated by the Earth is lost to space.
Carbon dioxide is a naturally occurring gas that is released and absorbed in a natural cycle.
One illustration of that complex cycle is that animals, such as human beings, exhale carbon dioxide, which is absorbed by plants. The plants use the carbon dioxide and then release oxygen that humans can inhale. Fossil fuels release carbon dioxide when they're burned, throwing the natural cycle out of balance and increasing the amount of carbon dioxide in the atmosphere. The Third Assessment Report's release gained worldwide media attention and prompted speculation about such effects as the flooding of tropical islands, the flow of refugees from agricultural failure into Europe from Africa, and the disappearance of species that depend on specialized environments. The Working Group II report, released in February, painted a picture of tropical farmers unable to grow crops, a spread of tropical diseases such as malaria and cholera, and an increase in flooding from both heavy rains and rising seas.