Image courtesy of Godard Institute for Space Studies/NASA
Editor's note: Exactly 20 years ago, on June 23, 1988, James Hansen of the NASA
Goddard Institute for Space Studies testified before a Senate committee
that he could state with "99 percent confidence" that a recent,
persistent rise in global temperature was occurring, and had long been
expected. That landmark statement, and the dawn of the global warming
discussion, was covered by Andy Revkin, then a DISCOVER senior editor
and now an environmental reporter for The New York Times.
Here we republish Revkin's groundbreaking 1988 article that helped begin to raise awareness of the issue. DISCOVER's new science and politics blog, Reality Base, also has an interview with Revkin about what's happened with regard to global warming over the past 20 years.
On June 23 the United States sizzled as thermometers topped 100 degrees in 45 cities from coast to coast: 102 in Sacramento; 103 in Lincoln, Nebraska; 101 in Richmond, Virginia. In the nation's heartland the searing heat was accompanied by a ruinous drought that ravaged crops and prompted talk of a dust bowl to rival that of the 1930s. Heat waves and droughts are nothing new, of course. But on that stifling June day a top atmospheric scientist testifying on Capitol Hill had a disturbing message for his senatorial audience: Get used to it.
This wasn't just a bad year, James Hansen of the NASA Goddard Institute for Space Studies told the Senate committee, or even the start of a bad decade. Rather, he could state with "99 percent confidence" that a recent, persistent rise in global temperature was a climatic signal he and his colleagues had long been expecting. Others were still hedging their bets, arguing there was room for doubt. But Hansen was willing to say what no one had dared say before. "The greenhouse effect," he claimed, "has been detected and is changing our climate now."
Until this year, despite dire warnings from climatologists, the greenhouse effect has seemed somehow academic and far off. The idea behind it is simple: gases accumulating in the atmosphere as by-products of human industry and agriculture—carbon dioxide, mostly, but also methane, nitrous oxide, ozone, and chlorofluorocarbons—let in the sun's warming rays but don't let excess heat escape. As a result, mean global temperature has probably been rising for decades. But the rise has been so gradual that it has been masked by the much greater, and ordinary, year-to-year swings in world temperature.
Not anymore, said Hansen. The 1980s have already seen the four hottest years on record, and 1988 is almost certain to be hotter still. Moreover, the seasonal, regional, and atmospheric patterns of rising temperatures—greater warming in winters than summers, greater warming at high latitudes than near the equator, and a cooling in the stratosphere while the lower atmosphere is warmer—jibe with what computer models predict should happen with greenhouse heating. And the warming comes at a time when, by rights, Earth should actually be cooler than normal. The sun's radiance has dropped slightly since the 1970s, and dust thrown up by recent volcanic eruptions, especially that of Mexico's El Chichon in 1982, should be keeping some sunlight from reaching the planet.
Even though most climatologists think Hansen's claims are premature, they agree that warming is on the way. Carbon dioxide levels are 25 percent higher now than they were in 1860, and the atmosphere's burden of greenhouse gases is expected to keep growing. By the middle of the next century the resulting warming could boost global mean temperatures from three to nine degrees Fahrenheit. That doesn't sound like much, but it equals the temperature rise since the end of the last ice age, and the consequences could be devastating. Weather patterns could shift, bringing drought to once fertile areas and heavy rains to fragile deserts that cannot handle them. As runoff from melting glaciers increases and warming seawater expands, sea level could rise as much as six feet, inundating low-lying coastal areas and islands. There would be dramatic disruptions of agriculture, water resources, fisheries, coastal activity, and energy use.
"Average climate will certainly get warmer," says Roger Revelle, an oceanographer and climatologist at the University of California at San Diego. "But what's more serious is how many more hurricanes we'll have, how many more droughts we'll have, how many days above one hundred degrees." By Hansen's reckoning, where Washington now averages one day a year over 100 degrees, it will average 12 such scorchers annually by the middle of the next century.
Comparable climate shifts have happened before, but over tens of centuries, not tens of years. The unprecedented rapid change could accelerate the already high rate of species extinction as plants and animals fail to adapt quickly enough. For the first time in history humans are affecting the ecological balance of not just a region but the entire world, all at once. "We're altering the environment far faster than we can possibly predict the consequences," says Stephen Schneider, a climate modeler at the National Center for Atmospheric Research in Boulder, Colorado. "This is bound to lead to some surprises."
Schneider has been trying to generate interest in the greenhouse effect since the early 1970s, although largely unsuccessfully. Frightening as the greenhouse effect is, the task of curbing it is so daunting that no one has been willing to take the necessary steps as long as there was even a tiny chance that the effect might not be real. Since greenhouse gases are chiefly the result of human industry and agriculture, it is not an exaggeration to say that civilization itself is the ultimate cause of global warming. That doesn't mean nothing can be done; only that delaying the effects of global warming by cutting down on greenhouse-gas emissions will be tremendously difficult, both technically and politically. Part of the problem is that predicting exactly what will happen to the local climate, region by region, is a task that's still beyond the power of even the most sophisticated computer model.
