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Is the World Getting Hotter?

The Potential Effects of Global Climate Change on the United States: Draft Report to Congress Printing Office in two volumes

edited by Joel B. Smith, edited by Dennis A. Tirpak
US Environmental Protection Agency, forthcoming from the US Government

State of the World 1988: A Worldwatch Institute Report on Progress Toward a Sustainable Society

by Lester R. Brown, by William U. Chandler, by Alan Durning, by Christopher Flavin, by Lori Heise, by Jodi Jacobson, by Sandra Postel, by Cynthia Pollock Shea, by Linda Starke, by Edward C. Wolf
Norton, 237 pp., 9.95 (paper)

A Matter of Degrees: The Potential for Controlling the Greenhouse Effect

by Irving M. Mintzer
World Resources Institute, 60 pp., $10.00 (paper)

The End

by Larry Ephron
Celestial Arts Press, 240 pp., $8.95


For most Americans, last summer was one of the hottest on record. Some experts said the heat may have been a sign of what to expect from the “greenhouse effect”—the increased levels of carbon dioxide in the atmosphere as the result of burning fossil fuels. The carbon dioxide traps the sun’s infrared radiation close to the planet’s surface and causes the temperature to rise. Other experts said no: last summer’s heat was simply weather.

This debate is not new. In 1896 and 1908, the great Swedish scientist Svante Arrhenius published papers setting forth what we know now as the greenhouse hypothesis. He calculated that if enough coal and oil were burned to double the concentration of carbon dioxide that existed in the atmosphere before the Industrial Revolution, the temperature of the planet would increase between four and six degrees Celsius, or seven to ten degrees Fahrenheit. In the decades that followed, other researchers occasionally touched on his work. Almost fifty years ago, in 1939, G.S. Callender, a British meteorologist, speculated that a warming induced by carbon dioxide was already underway. But most scientists were otherwise occupied and, anyway, the prevailing view held that the oceans, which contain sixty times as much carbon dioxide as the atmosphere, would serve as a convenient dump, soaking up the gas as speedily as people could create it.

Then, in 1957, Roger Revelle and Hans Suess of the Scripps Institute of Oceanography in La Jolla, California, demonstrated that the upper layers of the ocean would not absorb carbon dioxide anywhere near as rapidly as had been assumed. This discovery may someday be remembered as defining the most important limit in an age of limits, the central awkward fact of a hot and constrained life. “Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past, nor be repeated in the future,” wrote Revelle and Suess. “The experiment,” they added with morbid understatement, “if adequately documented, may yield a far-reaching insight into processes determining weather and climate.”

The thirty years since have been spent compiling that adequate documentation—what quickly was dubbed the greenhouse theory became one of the main preoccupations of atmospheric science. The first task, since no one even knew for certain that carbon dioxide was increasing, was to measure its concentration in the atmosphere. In 1958, as a part of the International Geophysical Year, a Scripps scientist established a monitoring station 11,150 feet up the side of Mauna Loa in Hawaii, high enough above civilization for uncontaminated readings. In fairly short order, the data revealed a clear pattern: there was an annual fluctuation, with carbon dioxide decreasing in the springtime as plants wake up and take in carbon dioxide through photosynthesis, and increasing in the fall as leaves die, but this fluctuation peaked at a steadily higher level each year. Carbon dioxide was marching upward—concentrations in the atmosphere were rising at a rate of about one part per million each year. The rate has since increased to 1.5 parts per million annually for a total concentration to reach this year about 350 parts per million. So that, at least, was beyond dispute.

Meanwhile, researchers were working out a model of the greenhouse effect, studying other planets, for instance, to see what effect carbon dioxide had on them. Mars, with only trace amounts of carbon dioxide, reradiates most of its heat straight back to space—its average temperature is only 220 Kelvin (about 64 degrees below zero Fahrenheit), compared with 288 K (59 degrees Fahrenheit) on earth, where the atmosphere is .03 percent carbon dioxide, and 700 K (800 degrees Fahrenheit) on Venus, where carbon dioxide levels approach 97 percent. Without the greenhouse effect, Venus would be approximately the same temperature as the earth.

Other scientists, working backward with the aid of glacial cores, established the pre-industrial concentration of carbon dioxide at about 280 parts per million. And slowly researchers began to redo Arrhenius’s calculations, this time using enormously complicated general climate models to predict the outcome of a doubling of carbon dioxide. In 1979, a team of experts assembled by the National Academy of Science forecast a possible 2–3.5 degree Celsius (approximately three to six degree Fahrenheit) warming, and two years later a similar all-star team decided there were no new results that would “necessitate substantial revision” of the estimates. In 1984, an Environmental Protection Agency report predicted global temperature increases of 3.6 degrees Celsius (6.5 degrees Fahrenheit) by 2040; and a year later, in Villach, Austria, a global colloquium organized by the United Nations Environmental Programme and the World Meteorological Organization concluded, “It is now believed that in the first half of the next century a rise of global mean temperature could occur which is greater than any in man’s history.”

As agreement on the general outlines emerged, more specific forecasts began to appear. The heat would increase the most at the poles (perhaps as much as fifteen degrees Fahrenheit). The temperature could top 100 degrees seventy-eight days each year in Dallas, up from nineteen days at the present. Droughts would become more likely across the grain belt, and forest and brush fires would increase. Scientists began to work out the consequences of these changes. Some were hard to imagine. The sea level could rise a meter or more, because of glacial and perhaps polar melting, and because of the thermal expansion of a warmer ocean. As a result half or more of America’s coastal wetlands, such as those in Louisiana, would be inundated. Wheat might grow in the north of Russia (as a recent report by a UN-sponsored research group argues).* Horrendous trouble would occur in places like Bangladesh, where much of the population lives on flood plains. Some consequences were immediately understandable—New York City’s street bumps, called hummocks, increase dramatically with sustained temperatures above 90 degrees, according to the city’s Bureau of Highway Operations. The draft EPA report on the effects of a warming in America—the most extensive report of its type so far—includes various projections on everything from mosquito-borne cattle disease to Great Lakes shipping.

Meanwhile, still other theorists were finding more causes for alarm. A variety of gases existing in much smaller concentrations than carbon dioxide—including nitrous oxides, methane, and the chlorofluorocarbons (already blamed for destroying the earth’s ozone layer)—were found to act like carbon dioxide in the atmosphere. In fact, some researchers said, these gases—particularly methane, the flammable ingredient of natural gas—could be contributing nearly as much as carbon dioxide to the warming trend.

That is about where affairs stood at this time last year. Carbon dioxide was increasing and the scientific community had reached a consensus (though not, as we shall see, without some doubters) that the greenhouse effect was real, and that therefore the temperature was destined to increase dramatically in the near future. But “destined,” “future,” “projected,” “predicted,” “forecast,” “expected”—these are the words that land a topic on Nova, not the Evening News. From a scientific point of view, the question of whether the warming had actually begun was only one of several necessary tests of the greenhouse theories. From a political point of view, actual onset of the heat was a precondition for a serious discussion of the theories.

The search for what greenhouse theoreticians called the “warming signal” had been underway for some time, but it was not an easy task. We have had reliable temperature records for less than 150 years, so establishing a baseline from which to record any deviation has been difficult. Two enormous studies, however—one by researchers at East Anglia University, the other led by James Hansen of NASA’s Goddard Institute in Manhattan—took the millions and millions of temperature readings available from the last hundred years and attempted to plot them. Each group, to make a very long story short, concluded that global temperatures rose about 0.6 degrees Celsius during the last century (about one degree Fahrenheit), a figure “consistent with” though slightly lower than the greenhouse models predicted. Hansen’s group concluded that three of the four hottest years on record took place in the first half of the 1980s. The question was: Was this proof of a warming or a matter of mere natural climatic variability? Was it signal or was it “noise,” the random fluctuation that marks climate?

Then came the spring and summer of 1988. By midsummer Hansen could say that, barring an extremely cold fall, it would be the hottest twelve months on record for the globe. The awesome drought, which destroyed one third of the country’s harvest, had everyone slightly on edge even before the heat took hold in the East. But was it the greenhouse effect? On June 23, testifying before the Senate Committee on Energy and Natural Resources, Hansen was quoted as saying that it was. Actually, Hansen’s conclusion that the warming “signal” had become apparent was not based on 1988. In addition to the hundred-year finding of a 0.6 degree Celsius increase, Hansen had figured the increase over the last thirty years to be about 0.4 degrees Celsius (0.7 degrees Fahrenheit). In both cases the observed changes were about three times the standard deviation. “When we’re talking about that degree of deviation,” he said in a recent interview, “we have to feel it’s pretty unlikely to be chance fluctuation. There’s no point at which it automatically switches over, but when you get to three times the standard deviation, you’re at a level where it’s unlikely to be an accidental warming.”

This was not the same thing as saying that last summer’s heat was the result of the greenhouse effect—in fact, Hansen’s calculations showed that it would likely take until about 1990 for the effects to be felt locally. But reporters were correct in a larger sense when they said Hansen thought the warming had begun. He would have thought the same thing if it had been a cold, wet summer—but if it had been a cold, wet summer he wouldn’t have made the papers, much less the front page. “I would say there was not a sharp change in my assessment—there was more of a sharp change in the attention, which had a lot to do with the temperature the day I testified,” he said.

Hansen’s proclamation seems to have had the effect of convincing people in the street that there may be trouble in the sky—complete oblivion has turned to a nervous fretfulness, but not an all-out conversion to the greenhouse theory. Which is understandable—other dire predictions have failed to materialize in the past, after all. (There is too much oil at present, not too little as so many feared during the 1970s.) And even among the scientists committed to the greenhouse theory, there is debate about whether the warming has actually shown up, or if 1988 was a freak. Stephen Schneider, of the National Center for Atmospheric Research in Boulder, Colorado, told the Senate in August:

  1. *

    M.L. Parry, T.R. Carter, and N.T. Konijn, eds., The Impact of Climatic Variations on Agriculture (Kluwer Academic Publishers, 1988).

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