Debate over a Frozen Planet

By Natalie Angier

A major study supports the grim prediction of nuclear winter

It is two weeks after a major nuclear war, and the searing white flashes of 25,000 bombs have faded into a black drizzle of radioactive fallout. Yet Armageddon is not complete: for miles above the earth, sunlight is blotted out by plumes of smoke from the vast conflagrations in which the major cities of the Northern Hemisphere have been consumed. This thick veil of soot and dust slowly circulates through various layers of the atmosphere, blanketing entire continents, creating a world of frigid darkness. As ground temperatures plummet by as much as 40DEG F and the sun is obscured, crops in Iowa, Nebraska and the Ukraine in the Soviet Union perish.

This grim scene is a possible approximation of the aftermath of nuclear war, according to a study released in Washington last week by the National Research Council, the principal operating agency of the nation's most august scientific body, the National Academy of Sciences. Three years ago, Paul Crutzen, a Dutch meteorologist who is now director of the Max Planck Institute for Chemistry in Mainz, West Germany, suggested that a cataclysmic nuclear war could be followed by a period of icy gloom. Later, Atmospheric Scientist Richard Turco of R&D Associates in Marina del Rey, Calif., Astronomer Carl Sagan of Cornell University and a handful of other researchers elaborated on the idea, concluding that the cold, which they called nuclear winter, could last for months. Some scientists have disagreed with a few of the more extreme predictions of this hypothesis, which has been given its first official stamp of credibility by the 193-page N.A.S. report. Declared Committee Member Turco: "This legitimizes the problem."

The study, which was commissioned in 1983 by the Department of Defense's nuclear agency, cautioned that uncertainties remain in many of the calculations. Even so, said George E Carrier, an applied mathematician at Harvard University who was chairman of the 18-member committee, the N.A.S. findings were "consistent" with the original studies, which predicted global cooling and severe hardship for any survivors. The panel recommended that high priority be given to serious research to try to answer some of the more elusive questions that the nuclear-winter theory has raised.

The answers could eventually play a role in formulating the nation's defense strategy. Already one U.S. Government defense study, prepared by the Center for Aerospace Doctrine, Research and Education in Montgomery, Ala., has based its policy analyses on the assumption that the nuclear-winter theory is correct. Says Theodore Postol, a strategic-arms consultant at Stanford University: "I see this as a vehicle to raise questions about our whole nuclear strategy."

Science Adviser George Keyworth II and other members of the Reagan Administration are citing nuclear winter as further justification for developing the Star Wars defense system, which might employ space-based weapons to destroy incoming missiles. With such a system in place, argues Keyworth, neither side would be tempted to strike first, hence the risk of a major war and its climatic consequences would be diminished. But Postol and many other nuclear strategists insist that Star Wars would more likely force the Soviets also to build advanced weapons and thus increase the threat of global holocaust.

The U.S. and the Soviet Union together now have about 50,000 weapons with an explosive power of 13,000 megatons in their nuclear arsenals. Carrier's committee studied a hypothetical war in which about half these weapons were used, both on military targets and on the 1,000 largest cities in the North Atlantic Treaty Organization and Warsaw Pact countries. The blasts from such a war, the report concluded, would immediately send 10 million to 24 million tons of dust into the stratosphere. Another 20 million to 650 million tons of smoke coming from the blasted cities and forests would be deposited mostly in the troposphere. Vast clouds of dust and smoke would spread across entire continents within days, and the Northern Hemisphere could be blocked from 99% of the sun's light.

Those grim findings could enhance the prospects for a major federal study. In response to the N.A.S. report, the White House may ask for at least part of a $50 million investigation of nuclear winter that is under consideration. Global weather patterns and the behavior of forest fires are two areas likely to figure prominently in the study.

Whether nuclear winter would actually occur after an atomic conflagration is debatable, because the subject involves a complex amalgam of chemistry, physics and meteorology. Indeed the researchers who originated the concept stumbled upon it from several different directions. Many scientists had considered the climatic effects of nuclear war to be relatively insignificant until Paul Crutzen, together with U.S. Chemist John Birks, on leave from the University of Colorado, drew attention to a previously overlooked problem: soot from fires. In 1981, while researching a journal article on the atmospheric consequences of nuclear war, the two assumed that at least 386,000 sq. mi. of forest could burn during a nuclear holocaust. They estimated that the enormous columns of smoke rising into the troposphere--where weather is generated--and possibly into the stratosphere would be enough to block out nearly all sunlight in many areas for weeks and maybe months.

In the U.S., Sagan and Turco, together with Brian Toon, Thomas Ackerman and James Pollack (the three are now at NASA's Ames Research Center in Moffett Field, Calif), arrived at their own idea of nuclear winter in a somewhat more circuitous fashion. They devised a series of equations, growing out of a study of the Martian climate, to explain the cooling effects of dust in the atmosphere. The scientists analyzed everything from storms on Mars and volcanoes on earth to the possibility that an asteroid collision 65 million years ago was responsible for the demise of some of the dinosaurs. Finally, they realized that yet another event would kick up large amounts of obscuring dust: a nuclear war.

The Turco research team, hearing of Crutzen's work just before publication, was able to incorporate the effects of smoke and soot into its calculations. The following year, using a powerful Cray computer at Ames, they produced dozens of scenarios showing the climatic impact of nuclear wars of varying intensity and location. Christened TTAPS, after the authors' last initials, the study assumed a nuclear bombardment of 5,000 megatons. Targets were confined to the Northern Hemisphere but included sites ranging from missile silos to crowded cities. The study showed that the detonations would suck up more than 25,000 tons of dust into the troposphere and lower stratosphere. Vast firestorms would gallop through forests and urban areas alike. Says Steven Schneider, a climatologist for the National Oceanographic and Atmospheric Administration (NOAA), who has studied nuclear winter in detail: "Everything that burns--tables, chairs, human beings--is going to be turned into something that smokes."

The American scientists predicted that the clouds of smoke would combine into fewer, more enormous columns containing as much as 225 million tons of soot, which would collect in the troposphere and stratosphere (see diagram). Perhaps most startling of all, the calculations showed the smoke spreading from its origin in the Northern Hemisphere to the sky below the equator.

Even a relatively small conflict of 100 megatons could trigger a nuclear winter if the targets were cities, according to the TTAPS study. In sum, the researchers declared, the reality of nuclear winter raises the possibility that any aggressor will end up exterminating himself. Says Sagan: "A doomsday machine has been built cooperatively by the U.S. and the Soviet Union, but nobody knew it was there."

Since the appearance of the TTAPS paper, Nuclear Physicist Edward Teller and his colleagues at California's Lawrence Livermore Laboratory, a major weapons-research center, have sought to downplay the degree of destruction postulated by TTAPS. Writing in the authoritative research journal Nature last August, Teller noted that several factors may serve to thaw a nuclear winter: firestorms that loft smoke to a high altitude are very rare and depend on dense concentrations of fuel and precise weather conditions that allow all available oxygen to be consumed. Any slight incidence of cooling, Teller told TIME, "will be much less bad than the direct effects of a nuclear war."

Livermore calculations buttress Teller's theories. In one computer simulation of a detonation of a single-megaton explosion, Physicist Joyce Penner, who heads the laboratory's study of nuclear smoke, found that a column did indeed rise six miles into the sky, but that half the smoke dropped quickly into the troposphere. The 50% that remained aloft, Penner estimated, contained nearly three times the condensation needed to produce rain. This finding suggested that even smoke in the stratosphere, beyond the reaches of normal weather patterns, would create its own storm and fall back to earth.

Neither computers nor scientists on either side of the argument have yet been able to answer the major questions about conditions following a nuclear attack: How high would a column of smoke rise from an urban obliteration? How much smoke would fall back to earth? Would the sun cause smoke plumes to heat up and rise higher into the stratosphere? How many megatons would have to be detonated in order to trigger nuclear winter? To get some answers, several federal agencies, including the Departments of Defense and Energy, the NOAA, NASA and the Environmental Protection Agency are about to launch a comprehensive study. In one of the survey's likely investigations, a plane will fly above large-scale forest fires, and on-board equipment will gauge particle size and the destination of the soot. High above the earth, satellites will photograph the smoke plumes.

The information gathered will then be fed into computers. Classified data on weapon yields and height of bursts will be included as well. Still, there is no guarantee that all the mysteries of nuclear winter can be unraveled. Says Alan Hecht, director of the National Climate Program Office in Washington: "We're being asked to solve a question that is at the heart of meteorology today." In other words, if scientists cannot predict tomorrow's weather, how can they foresee the aftermath of World War III?

Perhaps the ultimate meaning of the possibility of nuclear winter is the pressing need for effective arms-control agreements. Says Crutzen: "My advice to world leaders is, 'Come to your senses.' " --By Natalie Angler.

Reported by Barrett Seaman/Washington and Dick Thompson/San Francisco

HOW IT MIGHT HAPPEN

1.) Nuclear device is exploded over a populated area. Blast ignites fires.

2). Fires converge into a single firestorm. Heat from fire pumps a black column of smoke up through the troposphere. Some reaches the stratosphere.

3)Clouds of dust and smoke block sun's rays, then spread over vast areas of the globe, causing ground temperatures to fall. Much of the soot in lower troposphere is eventually washed out by rain, but clouds higher up continue to block sun for weeks or months. The particles that reach stratosphere could remain for a year or more.

With reporting by Barrett Seaman, Dick Thompson