Scientists Discount Drought Tie to ‘Greenhouse’ Warmth Trend
Evidence is mounting that the earth has entered the first stages of the long-forecast warming due to the “greenhouse effect,” but it is premature to link it to the current drought in the Midwest, scientists said Friday.
Nonetheless, the drought and high temperatures plaguing the United States are consistent with the predictions evolving from the greenhouse theory, experts said, and may portend a permanent increase in world temperatures due to a buildup of carbon dioxide in the atmosphere caused by the burning of fossil fuels.
One major consequence of the greenhouse effect is that agricultural areas of the Midwest and the Southeast would have a steady decline in average annual rainfall and would require extensive irrigation if productivity were to be maintained at current levels.
Unusually Hot
Scientists agree that the 1980s have been unusually hot and that this year is the hottest and driest of all. Climatologist James E. Hansen of the NASA Goddard Institute for Space Studies in New York City told the Senate Energy and Natural Resources Committee on Thursday that the heat and drought mark the beginning of the greenhouse effect.
Other scientists disagreed, however. “You can’t say that . . .,” said climatologist David Rind of the NASA institute. “Droughts have a multitude of causes.”
“Climate is, by definition, the average over many years,” said physicist John W. Firor of the National Center for Atmospheric Research in Boulder, Colo., “so there is no way you can tell if one year is part of a climate change or not.”
“What the drought does underscore, though, is the real possibility that, in the future . . . we may see droughts more frequently and more intensively than we have in the past,” said climatologist Alan Hecht of the National Oceanic and Atmospheric Administration, who is director of the National Climate Program.
“Given that possibility, this drought is important as a case study of how we respond to it and how we would anticipate and respond to any future drought,” he said.
Debated Effects on Climate
Scientists have debated the climatological effects of carbon dioxide since the late 1800s. The carbon dioxide allows the sun’s light to reach the earth’s surface and warm it, but absorbs heat that would otherwise be radiated into space--thus trapping heat just like the glass panes of a greenhouse.
“We’ve always had a greenhouse effect--that’s the least controversial theory in meteorology,” said climatologist Steven Schneider of NCAR. “If it didn’t work, Mars wouldn’t be a deep freeze, Venus wouldn’t be a hothouse, and the Earth wouldn’t be just right. The controversy is over how much added carbon dioxide will enhance the greenhouse effect.”
The amount of carbon dioxide in the atmosphere has grown from about 270 parts per million in the mid-1800s to about 345 parts per million now. A 1983 National Academy of Sciences report predicted that the level could reach 600 parts per million within 50 to 100 years if the use of fossil fuels continued to grow at then-current rates.
Such an increase, the academy predicted, would cause a global rise in temperature of as much as 9 degrees Fahrenheit--to temperatures that were last experienced during the age of the dinosaur. The warming would cause a marked change in wind patterns, resulting in a northward shift of precipitation in which moisture from the Equator would be carried closer to the poles. It would also cause a melting of the polar icecaps, accompanied by an increase in the oceans’ level and coastal flooding.
Climatologists estimate that the earth’s surface temperature has already increased between 0.5 and 1.25 degrees Fahrenheit since 1850. And that warming seems to be accelerating.
‘Warmest Year on Record’
Four of the hottest years on record have occurred during the 1980s, according to Hansen, and this year may be worse. “The first five months of 1988 are so warm globally that we conclude that 1988 will be the warmest year on record unless there is a remarkable, improbable cooling in the remainder of the year,” he told the Senate committee.
“It’s time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here,” he added.
But few other scientists seem willing to link this drought and the greenhouse effect so explicitly.
“On the one hand, we have mounting evidence that global temperatures have been rising for the last 100 years . . .,” said Hecht, “but, on the other hand, droughts in the United States are common--they are part of our climatology. So the mere fact that we have a drought now is really part of what has been the historic pattern.”
“We may be seeing the beginning of (the greenhouse effect),” said atmospheric physicist Michael E. Schlesinger of Oregon State University in Corvallis, “but there are just too few samples of data to be able to say that for sure.” The drought and the heat of the 1980s could equally well be due to differences in the output of the sun, particles and gases injected into the atmosphere by volcanoes or just natural variability, he said.
Little Impact Seen
In fact, Schlesinger said, some data, such as patterns of changes in the ocean’s temperature, suggests that the greenhouse effect has had little impact so far. “My concern is if we say now that this is the beginning of the greenhouse effect, and then it cools off because of natural variability, people will say, ‘Well, you fellows didn’t know what you were talking about,’ and would turn to other issues and do nothing about what is a very real problem.”
Nonetheless, virtually all the scientists contacted by The Times agreed that continued release of carbon dioxide into the atmosphere will have a major disruptive effect on Earth and that action should begin immediately to limit such emissions in the future by increasing the efficiency of energy use and by limiting the burning of fossil fuels.
