Symposium

Article excerpt

Q: Do Scientists have compelling evidence of global warming?

Yes: Rising sea levels worldwide and retreating Arctic glaciers are ominous signs.

Do scientists now have compelling evidence of global warming? The simple answer is: "Yes." We have strong evidence that the climate is changing and that human activities were the primary cause of the changes during the 20th century.

First, we have detected change. Global-average temperature is rising, precipitation patterns are changing, glaciers are retreating, sea levels are rising and Arctic sea ice is thinning. Second, we can attribute most of the observed warming of the last 50 years to human activities rather than to changes in solar radiation or other natural factors. Third, because human activities will continue to change the atmosphere's composition throughout the 21st century, global warming can be expected to continue. This will result in significant projected increases in global-average temperature, in the number of hot days, in heavy precipitation events and in higher sea level.

In 1997, representatives from more than 100 governments met in Kyoto, Japan, and agreed that industrialized countries should decrease their emissions of greenhouse gases. This decision was based in large part on the conclusions in the 1995 Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). This report presented a careful and objective analysis of all relevant scientific, technical and economic information. It was prepared and peer-reviewed by more than 2,000 experts in the appropriate fields of science from academia, government, industry and environmental organizations worldwide.

In 1995, as today, the overwhelming majority of governments and scientific experts recognized that while scientific uncertainties existed, strong scientific evidence demonstrated that human activities were changing Earth's climate and that further human-induced climate change was inevitable. Hence, scientists and governments alike recognized in 1995 and reaffirm today that the question is not whether climate will change in response to human activities, but rather where (regional patterns), when (the rate of change) and by how much (magnitude).

The scientific evidence also indicates that climate change will, in many parts of the world, adversely affect human health, ecological systems (particularly forests and coral reefs), and important socioeconomic sectors, including agriculture, forestry, fisheries, water resources and human settlements. Developing countries are the most vulnerable, primarily because a larger share of their economies are in climate-sensitive sectors, and they do not have the institutional and financial infrastructures to adapt to climate change.

Since 1995, confidence in the ability of models to project future climate change has increased. This is because of their demonstrated performance in simulating key features of the climate system across a range of space and time intervals, most particularly, their success in simulating the observed warming during the 20th century. Certainly, models cannot simulate all aspects of climate. For example, they still cannot account fully for the differences in the observed trends in surface and midtropospheric temperatures during the last two decades.

On Jan. 22 in Shanghai, China, the IPCC released its latest report on climate-change science. This report was prepared by more than 600 scientists, peer-reviewed by more than 300 expert reviewers and further peer-reviewed and approved by nearly 100 governments. During the next two months, the IPCC will release its third assessment report on impacts and vulnerability and on options for reducing greenhouse gas emissions. Both the 1995 and 2001 IPCC reports say that the Earth's climate is warming, that human activities are implicated in the observed warming and that the Earth will warm several degrees Fahrenheit during the next 100 years as compared with only about 1 degree during the last 100 years. …