Science & Technology
IS THE WORLD HEATING UP? WELL, JUST LISTEN
On Jan. 26, the seas will reverberate with the sound of science. Researchers will switch on a loudspeaker in the ocean near Heard Island, 2,550 miles southwest of Perth, Australia. From a depth of 600 feet, the speaker's booming bass notes, louder than a jet plane at takeoff, will race through the briny deep to microphones scattered all over the world.
This listening system will be a giant thermometer. The speed of sound varies with temperature, and if researchers measure the pace of this ocean music for 10 to 20 years, they may find the answer to the most critical environmental question of the times: Is the earth catching a fever from greenhouse gases that humans pump into the atmosphere? Scientists don't "totally accept that global warming is occurring," says University of Washington physicist Robert C. Spindel, the project's director. "This may be the only way to get a reasonable answer in a reasonable amount of time."
BACKING OFF. Answers are what policymakers need. For nearly a decade, scientists have probed sea ice and permafrost, scoured weather records, and harnessed supercomputers and satellites to learn how the climate is changing. They've found that glaciers are receding and that the 1980s were the warmest decade in modern times--tantalizing signs of warming. But other indications, such as a predicted shrinkage of the polar ice caps, aren't occurring, says University of Illinois meteorologist John E. Walsh. "The surprise," he adds, "is that we don't see more evidence of climate trends." Thus, some scientists have scaled back their predictions of how much the earth may heat up.
The lack of definitive data is sharpening the debate over policy. Under the auspices of the United Nations, representatives from more than 130 countries will gather near Washington on Feb. 4 to start work on an international treaty, to be ready by 1992, aimed at slowing global warming. The European Community and Japan, among others, want to cap emissions of carbon dioxide, the key greenhouse gas, at 1990 levels. That's a modest proposal compared with Australia's plan to cut such emissions by 20%.
Even so, Bush Administration officials are expected to oppose emission targets, which they see as too costly, given the evidence so far on warming. If they're right, they may save the world lots of money and trouble. But U. S. recalcitrance will make any accord harder to reach, which critics deplore. "If the U. S. won't take modest steps, how can other countries be expected to do so?" asks William A. Nitze, a former State Dept. climate negotiator who is president of the nonprofit Alliance to Save Energy.
Everyone agrees that greenhouse gases will alter the climate somehow. It's a matter of physics; the gases trap extra heat from the sun. But from there, uncertainty reigns. There's now a consensus that the additional heat could raise the average temperature of the earth 2 to 7 degrees Fahrenheit by the middle of the next century. That's down from the original dire predictions. But it's still a wide range, and scientists don't agree on what either extreme would mean.
The difficulty in guessing right stems partly from the lack of clear historical patterns. Consider U. S. temperature records, which have been corrected for such variations as the growth of cities, which heat up their surroundings. The U. S. warmed between 1885 and 1930, cooled in the '40s, warmed in the '50s, cooled again during the '60s and '70s, then warmed in the '80s. From all that, only one consistent trend emerges. "The noticeable thing is the dramatic warming in the nightly minimum temperature," says meteorologist Richard R. Heim Jr. of the National Oceanic & Atmospheric Administration's National Climatic Data Center in Asheville, N. C. In the 1950s, nights were more than 26F cooler than days, on average. By 1987, nights averaged only 24F cooler. And new data from the Soviet Union and China show that the phenomenon may be worldwide.
COMPLEXITY. But why, and what might the consequences be? Increased cloud cover could be the cause. Low-atmosphere clouds cool the earth by day--a 3% increase would offset the warming from a doubling of greenhouse gases--and also insulate the ground at night. Some shipboard observations show that cloud cover is increasing. And scientists are trying to determine if that's true. The implications could be profound. "If the nights warm up, the growing season will be longer," says University of Virginia climatologist Patrick J. Michaels, a greenhouse doubter. "Instead of apocalypse, we may end up with a more beneficial climate."
That view may overlook the earth's complexity. Scientists don't know exactly how clouds form or how they interplay with factors such as the oceans to affect climate. For instance, daytime cooling from increased low clouds might be balanced by warming from thin, high clouds or increased water vapor, a potent greenhouse gas. Pollution is another variable. Sulfate particles spewed from cars and power plants help clouds to form. After examining ice cores plucked from Greenland glaciers, Paul A. Mayewski of the University of New Hampshire found that sulfate levels rose in the '60s and '70s before stabilizing in the '80s, presumably because of pollution controls. "That could explain a cooling from the 1950s to the 1970s and a warming in the 1980s," he says.
So many loose ends have helped persuade scientists to scale back their predictions of disaster. When scientists organized by the International Panel on Climate Change (IPCC), a global assembly of researchers, began sifting the data a few years ago, some felt that sea levels could rise a meter or more by 2030, flooding countries such as the Netherlands and Bangladesh. But when the group finished its report late last year, it predicted a rise of only 8 to 29 centimeters. That's partly because of an intriguing trend at the south pole. Analyses by glaciologist Charles R. Bentley of the University of Wisconsin show that, because of slightly warmer temperatures, enough water is pulled from the ocean and dumped as snow on Antarctica to slow the oceans' rise by 3 centimeters a decade. "We think sea level rise is an indicator of global warming," says Mark F. Meier, director of the Institute of Arctic & Alpine Research at the University of Colorado. But he adds: "We don't understand it very well."
Small wonder, then, that a second IPCC group studying how global change will affect such things as food production, has just shrugged. In a report due at the end of January, the group found it impossible to tell whether climate change will make it easier or harder to feed the world's peoples.
Predicting the fate of the world's breadbaskets would be easier if computer modeling were more advanced. One problem is that models lack enough precise historical data on everything from rainfall and ocean currents to cloud and ice cover. "We are starved for measurements," says Warren M. Washington, a climate modeler at the National Center for Atmospheric Research.
The Heard Island experiment could help, since the oceans are key indicators of change. Air temperatures haven't risen as fast over the past 50 years as the models have predicted, says Walter H. Munk of the Scripps Institution of Oceanography. So in theory, the seas, which account for two-thirds of the earth's surface, could be soaking up the missing heat. That could have big consequences. Small variations in sea temperatures are one factor in global weather and ocean current changes that can wipe out fish populations and bring drought or floods to far-flung places. So, Munk, Spindel, and their colleagues devised the scheme to measure sea temperatures. If the ocean warms a tiny fraction of a degree, the sound will travel a few milliseconds faster over a thousand-mile path. All the scientists needed was a powerful loudspeaker, provided by the Navy, and a spot such as Heard Island, which faces vast expanses of open ocean in all directions.
There is one catch: It will take decades of listening to spot a clear trend, since any short-term pattern may not be conclusive. "Even if we see a trend that's sticking out like a sore thumb, we don't know if it is the greenhouse effect or just part of a natural cycle," says climatologist Joel Susskind of the National Aeronautics & Space Administration's Goddard Space Flight Center.
To help decide such questions, scientists are looking backward--in ice cores, tree rings, and weather data--though there are few pat answers. Studying satellite records of snow cover over North America, climatologist David A. Robinson of Rutgers University found that the late '80s and 1990 were far less snowy than the '70s--potential evidence of warming. But then he discovered that the '70s were unusually snowy. So the '80s "might just be a return to what we saw earlier." Before scientists can conclude that the earth is warming, he adds, they will need to find "multiple indicators all pointing in the same direction."
In the meantime, many environmentalists and the IPCC working group on global warming policy argue that the cost of taking some action now would be small compared with waiting too long. "If the climate changes rapidly in whatever direction, developing countries that rely on subsistence agriculture and natural resources will be very vulnerable," Nitze says. The IPCC will recommend a "no-regrets" policy, a mixture of energy conservation and reforestation that makes economic sense even without climate change. Those actions, some experts say, would help stabilize greenhouse gas emissions. That may be a wise move. By probing the seas, skies, and land, scientists eventually will gather enough
evidence to unravel the complexities of climate. But until then, prudence may be the better part of valor.John Carey in Washington