No Major Warming Found in Studies of U.S. Climate
A team of government scientists has concluded after examining temperature and rainfall records going back nearly 100 years that there is no evidence of significant warming or changes in precipitation in the contiguous United States.
Nor are there any indications in the weather records so far to substantiate some global warming models that suggest that the “greenhouse effect” will result in drier summers and wetter winters in the central regions of the continent, the scientists said.
“The most important result of this study is that there is no statistically significant evidence of an overall increase in annual temperature or change in annual precipitation for the contiguous U.S. (between) 1895 and 1987,” they concluded.
While the scientists said their study should not be interpreted as debunking the greenhouse effect, it appeared certain to add to a growing scientific controversy over when and where the postulated global warming would take place.
“We’re not saying this makes the greenhouse effect go away. I’m personally concerned about the greenhouse effect,” climate research scientist Kirby Hanson said in a telephone interview from Miami.
The findings, published in the January issue of the American Geophysical Union’s Geophysical Research Letters, were the result of research by three scientists with the National Oceanic and Atmospheric Administration. The co-authors of the study were George A. Maul and Thomas R. Karl.
Last July in the midst of a scorching heat wave and drought in the Midwest, James Hansen of the National Aeronautics and Space Administration’s Goddard Institute startled members of Congress when he testified that the unusually hot conditions could be the forerunners of the long-feared greenhouse phenomenon.
Global Readings
Hansen had previously examined temperature readings from around the globe going back 100 years. On the basis of detailed studies, Hansen concluded that global temperatures had risen about 0.6 degrees Celsius (about one degree Fahrenheit) during the last century. He said that figure was “consistent with” though slightly lower than temperatures predicted by greenhouse computer models. He could not be reached for comment Wednesday.
Largely based on Hansen’s testimony, there has been a flurry of legislation introduced in Congress and the California Legislature calling for new restrictions on emissions of gases such as carbon dioxide, chlorofluorocarbons and methane in order to slow down global warming.
Hansen also reported that on a worldwide basis, three of the four hottest years on record took place in the first half of the 1980s.
Another scientist not associated with the study, Peter H. Gleick of a Berkeley-based research institute that has undertaken numerous greenhouse studies, said, “What that study is saying is that if you look at temperature records over the lower 48 states, there appears to be no evidence yet that the greenhouse effect is upon us. That is different than saying there is no greenhouse effect.”
The greenhouse effect refers to a buildup of carbon dioxide and other heat-trapping gases in the atmosphere that act like the transparent glass ceiling of a greenhouse. Scientists believe that the greenhouse effect will become a problem as humans continue to burn large amounts of fossil fuel, which releases large amounts of carbon dioxide into the atmosphere.
The NOAA scientists said they found no such temperature rise in the lower 48 states, a finding that was in keeping with Hansen’s estimates that he would not expect to see greenhouse effects in the United States until about 1990.
“The results of all tests indicate no significant trend over the 93-year period,” they reported.
The three researchers specifically looked at weather records for the Great Plains states of Montana, Nebraska, Wyoming and North and South Dakota because some global climate models have suggested that a doubling of carbon dioxide levels in the atmosphere would produce drier summers and wetter winters in central regions of a continent.
No Change Detected
“There (is no) evidence of change in winter or summer precipitation on the northern plains during that (93-year) period,” the scientists said.
Overall, they said they found what other researchers had concluded earlier--a “marginally significant” increase in temperatures between 1895 and 1940, and a marginal decrease in temperatures from 1940 to 1987.
They also found that the only evidence of a statistically significant change were reports of increasing rainfall in the autumn during a limited 16-year period between 1970 and 1986. But they said the change could probably be best described as a “variation” and that it was too early to say what it meant.
Their findings were based on an examination of weather data dating back to 1895 from 6,000 weather reporting stations. They said that in making their calculations, they made allowances for observational bias.
But, Hanson of NOAA cautioned that there was “no direct relationship” between his group’s findings on the one hand and observed global warming on the other, as reported by Hansen of the Goddard Institute. Hanson of NOAA said that global warming theorists have from the beginning been the first to caution against attempting to predict the effects of global warming on any scale smaller than the entire world.
Predictions by global climate models become less reliable as scientists attempt to focus on smaller geographical areas.
Since the beginning of the Industrial Revolution, the amount of carbon dioxide--the principal greenhouse gas--has increased 25%. It is postulated that by the year 2030 or 2040 there will be a doubling of carbon dioxide concentrations in the atmosphere, which would warm the globe by 4 to 9 degrees Fahrenheit.
Such temperature increases, in the view of some, would produce major changes in climate that could result in catastrophic social, economic and political problems resulting from rising sea levels, shifting agricultural growing regions, and droughts.
