The Greenhouse Effect and Climate Change - The International Panel On Climate Change—a Scientific Consensus?

Global warming was only acknowledged as an international problem at the end of the twentieth century. At the world's first ecological summit, the 1972 Stockholm Conference, climate change was not even listed among the threats to society.

Climate-change science has been developing rapidly, leading observers to recognize the complexity of the issues. In order to understand the issue of climate change and any possible global warming, scientists worldwide gathered together in 1990 to exchange information. They formed the International Panel on Climate Change (IPCC), which is sponsored jointly by the United Nations Environment Program (UNEP) and the World Meteorological Organization. FIGURE 2.9
World carbon dioxide emissions by region, 1990–2025 The panel's mission was to advise the parties to the 1992 Global Warming Treaty. It received the input of nearly 400 of the world's climate experts from 25 nations.

The IPCC report was the most comprehensive summary of climate-change science to date. With regard to various statements about climate change, the scientists responded based on how sure they were of global warming: "virtually certain" (nearly unanimous agreement and no credible alternative), "very probable" (roughly a 90 percent likelihood of occurring), "probable" (a two out of three chance of happening), and "uncertain" (evidence does not support). The outcome indicated an international consensus on three basic statements related to global warming: that greenhouse gases do produce climate change, that there is a natural greenhouse effect, and that emissions resulting from human activities are contributing to the proliferation and effects of greenhouse gases.

A Landmark Judgment—The 1995 IPCC Report

In 1995 the IPCC reassessed the state of knowledge about climate change. The panel reaffirmed its earlier conclusions and updated its forecasts, predicting that, if no further action is taken to curb emissions of greenhouse gases, temperatures will increase 1.44 degrees to 6.30 degrees Fahrenheit by 2100. The panel concluded that the evidence suggested a human influence on global climate. FIGURE 2.10
The effect of forests on carbon dioxide concentrations The cautiously worded statement was a compromise following intense discussions. Nonetheless, it was a landmark conclusion because the panel, until then, had always said that global warming and climate changes could have been the result of natural variability. Despite acrimonious debate and challenges to the report, the conclusions have largely held up to scientific scrutiny.

The 2001 Update

The IPCC issued its third assessment report in 2001. It actually comprises four reports: Climate Change 2001: The Scientific Basis, Climate Change 2001: Impacts, Adaptation and Vulnerability, Climate Change 2001: Mitigation, and Climate Change 2001: The Synthesis Report. The IPCC's assessment covered the adaptability and vulnerability of North America to climate change impacts likely to occur from global warming. Among the suggested possible effects of global warming are:

• Expansion of some diseases in North America
• In coastal areas, increased erosion, flooding, and loss of wetlands
• Risk to "unique natural ecosystems"
• Changes in seasonal snowmelts, which would have effects on water users and aquatic ecosystems
• Some initial benefits for agriculture, but those benefits would decline over time and possibly "become a net loss"

Next IPCC Update Due in 2007

The IPCC plans to publish its fourth major assessment report in 2007. At meetings held in Paris during 2003 seven themes were selected for focus in the report:

• risk and uncertainty
• regional integration
• water
• key vulnerabilities
• adaptation and mitigation
• sustainable development
• technology