Looking for Mr. Greenhouse

Abstract

W hile oat bran and fax machines were instant hits last year, 1988 may go down in history as the year the greenhouse effect became fashionable. Future scholars seeking the spark that ignited this public passion may well focus on a sweltering 980 F day in the nation's capital. On June 23, 1988, as heat waves and drought seared the United States, a climate expert made headlines by telling Congress he was 99 percent sure the long-expected greenhouse warming had begun. NASA scientist James Hansen testified that the world had warmed significantly over the last century and that human activities had caused part of the temperature rise by releasing certain gases into the atmosphere (SN: 7/2/88, p.4). He also correctly predicted that 1988 would capture the highest mark on the century-long record of global average temperatures. Some climatologists have since joined Hansen in heralding the arrival of the greenhouse warming. Yet most have maintained a more cautious pose. Skeptical scientists acknowledge the world has warmed recently, and they agree that gases such as carbon dioxide, methane and chlorofluorocarbons are accumulating in the atmosphere, where they should eventually raise the average temperature of the Earth. But the vast majority of climate researchers are not willing to connect the rising levels of greenhouse gases with the climate warming. Such hesitation has puzzled a public that has watched media reports of rising global temperatures. Last summer's drought, heat wave and forest fires exacerbated the confusion, especially when several press reports claimed that Hansen blamed the hot summer on the greenhouse effect a connection he did not make. In the gap between laboratory and city street, several questions are brewing. Nonscientists are wondering why experts are wavering on this issue. If specialists can't yet say whether the greenhouse warming has taken effect, when will they know? While scientists are known as masters of equivocation, their hesitation on this issue does not stem simply from an aversion to definitive statements. Part of the problem lies in inaccuracies in the global temperature data, which may mean the Earth has not warmed as much as it seems. Resolving this issue will be one key to identifying Mr. Greenhouse. Scientists say they don't know when they will be able to offer an unequivocal statement, but they expect it may be at least five to 10 years away. The wait depends on many factors, particularly how the climate behaves during the 1990s.