Q: Is Man-Made Global Warming a Proven Environmental Threat?

Article excerpt

Yes: It bodes ill for health, agriculture and biodiversity.

BY ROBERT T. WATSON

A small, vocal minority of skeptics claims there is no scientific evidence to support the theory that man-made emissions of greenhouse gases will alter the Earth's climate. They claim that global warming is liberal, left-wing, claptrap science and a ploy by the scientific community to ensure funding for yet another "Chicken Little" scare. Others suggest that attempts to reduce greenhouse-gas emissions by changing energy- or land-use policies would needlessly cost the American taxpayer tens to hundreds of billions of dollars annually and that it is really part of an international conspiracy to undermine America's competitiveness in the global marketplace.

The truth, however, is quite different. The overwhelming majority of scientific experts believes human-induced climate change is inevitable. 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). This is the fundamental conclusion of a careful and objective analysis of all relevant scientific, technical and economic information by thousands of experts from academia, governments, industry and environmental organizations under the auspices of the U.N. Intergovernmental Panel on Climate Change.

The view of the majority of scientists is shared by 130 nations, including the United States, that signed and ratified the U.N. Convention on Climate Change. At a meeting in Berlin in March 1995, all parties to the treaty agreed that current actions to mitigate climate change are inadequate to protect society from the threat of human-induced global warming.

The good news is that the majority of energy experts, and energy organizations such as the World Energy Council, believe that dramatic reductions in greenhouse-gas emissions are technically feasible at little or no cost to society due to an array of energy technologies and policy measures. Many of these will have other benefits for society. For example, the use of more energy-efficient buildings and motor vehicles would reduce dependence on the importation of foreign oil and reduce air pollution at the same time. Although significant progress can be made with current technologies, a commitment to further research and development is essential.

However, we must keep in mind the following points about current scientific understanding of the climate system:

First, human activities undoubtedly are increasing atmospheric concentrations of greenhouse gases, which tend to warm the atmosphere. The most important greenhouse gas directly affected by human activities is carbon dioxide, which has increased by nearly 30 percent since 1700, primarily because of changes in land use (deforestation) and the burning of coal, oil and gas. In some regions of the world, human activities also have increased the atmospheric concentrations of aerosols (tiny airborne particles), which tend to cool the atmosphere.

Second, there is no doubt that the Earth's climate has changed during the last 100 years. The global mean air-surface temperature over the land and ocean has warmed between 0.6 and 1.1 degrees Fahrenheit, glaciers have retreated globally and sea level has risen 10 to 25 centimeters. Since the late 1970s there has been a decrease in Arctic Ocean ice and an unusual persistence of the El Nino conditions in the Pacific Ocean that affect severe weather patterns globally. In addition, the nine warmest years this century have occurred since 1980.

Third, while there has been, as yet, no definitive detection of a human-induced global-warming signal in the climate record, the evidence increasingly points in that direction. Comparing the observed changes in global mean temperature with model simulations that incorporate the effect of increases in greenhouse gases and aerosols suggests that the observed changes during the last century are unlikely to be due entirely to natural causes. …