‘Nuclear Winter’ : Theory to Stand Test of Fire, Smoke

In the three years since “nuclear winter” was first postulated, controversy has raged in the absence of any hard data to either support or refute the theory that smoke from fires ignited during a nuclear war would block out sunlight, plunging Earth into a deadly deep freeze.

But this fall, scientists plan to set a huge experimental fire in the Angeles National Forest near Los Angeles that is expected to furnish the first real information about what any survivors of a nuclear holocaust can expect.

Until now, computer simulations of the nuclear winter effect have been riddled with uncertainties because such models are only as good as the supporting data, and there is no reliable data available.

‘Nuclear Fall’ Theory

Even some early subscribers are backing away from the dire nuclear winter scenario, saying that recent mathematical models suggest something more akin to a “nuclear fall.” Instead of Arctic-like temperatures that could quickly lead to extinction of the human race, they envision less severe conditions that nevertheless could destroy crops and lead to mass starvation.

And many simply do not believe that any climatic changes could come close to the destruction caused by the initial explosions and intense radioactivity of a nuclear war.

“It has just been my argument versus your argument,” said David Auton, manager of the nuclear winter program of the U.S. Defense Nuclear Agency.

Nobody expects the unprecedented experiment to settle the dispute. “We’re not going to answer all, maybe any, questions in this one burn,” said Richard Turco, a Los Angeles atmospheric scientist who coined the “nuclear winter” phrase. “It’s kind of a learning experience.”

Indeed the true significance of the planned experiment may be that it marks the beginning of a new approach in investigating the hotly contested hypothesis.

Burn of 1,200 Acres

The fire could be set as early as a week from Monday or as late as December, depending on the weather. The fire is to burn 1,200 acres of chaparral in a rugged canyon in the San Gabriel Mountains, lofting a 10,000-foot plume of smoke.

Officials prefer not to publicize the actual site because an arsonist has been active in the area.

The fire is designed to burn itself out within a few hours. And since June, according to Scott Franklin, supervisor of vegetation management for the Los Angeles County, workers have been burning a broad fire break around the site that should prevent the fire from spreading out of control.

The fire site is in a part of the forest that is usually closed to the public, Philip Riggan, a U.S. Forest Service scientist, said. He said the only members of the public who will be given advance notice of the fire are a handful of occupants of summer homes in the woods near the canyon.

The smoke from the fire should be visible throughout the Los Angeles Basin, but residents of La Verne and San Dimas will have front-row seats. They need not worry, however, officials said.

There will be plenty of firefighting crews and even aircraft on hand to make sure that nothing goes wrong, according to Angeles National Forest officials who will supervise that effort.

And because of the potential for flooding, erosion and pollution as a result of large fires, officials representing many additional state, regional and local agencies will also have a say in how the burn proceeds, Riggan said.

“First and foremost, we’ve had to sit down and figure out what’s safe,” Franklin added. “If the science doesn’t fit, then they have to find another way of doing it.”

Specific conditions--such as humidity, temperature and wind direction--must be met before the fire will be lighted, he said. For example, the fire will be set only after officials determine that prevailing winds will push any smoke away from the Los Angeles Basin.

The fire is to be managed under the same guidelines that regulate all controlled burns in the county, some of which are two or three times larger in terms of acreage. Indeed the only unusual feature to this fire is all the scientific equipment that will be trained on it.

$750,000 Cost

The $750,000 experiment, two years in the planning, is funded by seven federal, state and county agencies, and several hundred people will be involved in either studying or containing the fire.

Data gathered from the experiment will also be used to test new methods of monitoring and fighting wildfires, to help scientists assess the contribution of fires to the smog in Los Angeles and to assess the so-called greenhouse effect, a theorized and potentially destructive global warming caused by growing carbon dioxide and other gases that trap heat in the atmosphere.

Scientists say it will be the most studied fire in history.

The array of instruments will be on the ground as well as airborne. A helicopter, for example, will swoop in just above the flames to gather gas samples. An updated version of the U-2 spy plane will circle five miles above the plume, using an infrared scanner to map the progress of the flames.

Some of these instruments were put through a test run last week during a controlled burn of several thousand acres of light brush near Magic Mountain.

The overriding goal of the experiment is to learn about smoke. “We have been burning things for hundreds of thousands of years, but we still don’t know much about what goes on,” said Larry Radke, an atmospheric scientist who will be leading one of the many teams studying the fire.

Smoke samples will be gathered to determine the blackness and size of the particles, two factors that influence how much sunlight could be blocked.

Also, if smoke particles form seeds of cloud droplets, any effects of a nuclear winter might be reduced because rainfall will cleanse some of the smoke from the skies. A sure sign of this phenomenon would be a capping cloud above the plume.

It will take many months for such data to be deciphered.

The challenge of studying the atmospheric consequences of nuclear war, as Turco put it, is that “it is a subject that is not amenable to experimentation.”

The effects of nuclear weapons have been studied for four decades, but until the nuclear winter theory came along, most of the research focused only on the “prompt effects”--the power of the shock wave, the intensity of the sun-hot pulse of light, the potency of the radioactivity.

Some studies did examine the effects of nuclear war on climate and weather, but none considered the specific effects of smoke, said Starley Thompson, an atmospheric scientist at the National Center for Atmospheric Research who is one of the proponents of “nuclear fall.”

1966 Study

One early study that did mention smoke was a 1966 Rand Corp. report for the Atomic Energy Commission. It touched on the possibility that smoke from forest fires set by nuclear blasts could affect the weather and cited a 3,800-square-mile fire in Canada’s Alberta province in 1950 that may have been responsible for a 10-degree drop in temperature in Washington, D.C., shortly afterward. But the study did not predict any global effects.

Other studies looked back at the way that Hamburg, Tokyo and Hiroshima burned in World War II, even though Hamburg and Tokyo were bombed only with conventional weapons, with an eye to assessing and projecting the effects of an urban fire set by a nuclear explosion. But, for the most part, smoke again was ignored.

And in simulated urban fires, smoke was still neglected. For instance, in a study funded by the Office of Civil Defense in the 1960s, called Project Flambeau, mock city blocks were constructed in the hills near Mono Lake, east of Yosemite. Square stacks of cut timber, each representing a house, were laid out in a grid and burned. Again, the goal was to study the fire itself, not the smoke.

The destructive potential of smoke came to light in 1981 through a chance calculation by two atmospheric chemists who had been concerned about another possible byproduct of nuclear war: smog.

Nuclear fireballs release huge amounts of nitrogen oxides, which, in the presence of sunlight and smoke, could result in deadly amounts of smog.

But in the course of their research, Paul Crutzen at the Max Planck Institute in West Germany and John Birks at the University of Colorado realized that the same smoke that helped create the smog might impede smog formation by blocking sunlight.

So they came up with a crude calculation, based only on smoke from nuclear-set forest fires, that estimated how much smoke might be produced and how much sunlight it would block.

Theory’s First Step

It turned out that several hundred million tons of smoke could be produced and could block 99% of the sun’s light. Their report, published in the Swedish journal Ambio in 1982 and titled “The Atmosphere After a Nuclear War: Twilight at Noon,” is now widely acknowledged as the first step toward a nuclear winter theory.

Turco, an atmospheric scientist at R & D Associates, an aerospace research company in Marina del Rey, took the calculation one crucial step further. He cut back on the smoke estimates from forests--which he felt were overestimated--but added smoke from a new source: burning cities.

It quickly became clear that the smoke could cause a major climatic catastrophe, he said.

Turco and a handful of scientists, including three from the National Aeronautics and Space Administration’s Ames Research Laboratory, then put together a comprehensive analysis that fully supported the new concept.

Nuclear winter was presented at a special conference in Washington--on Halloween, 1983. The historic work was published that December in Science magazine, the highly respected weekly publication of the American Assn. for the Advancement of Science.

Turco’s co-authors were NASA scientists O. Brian Toon, Thomas Ackerman and James Pollack--and Cornell astronomer Carl Sagan. This quintet soon became known as TTAPS, an acronym based on their last initials.

They summarized their findings in one sentence:

“We find that a global nuclear war could have a major impact on climate--manifested by significant surface darkening over many weeks, subfreezing land temperatures persisting for up to several months, large perturbations in global circulation patterns, and dramatic changes in local weather and precipitation rates--a harsh ‘nuclear winter’ in any season.”

Their study was full of caveats, some of which pointed out that the projections were based on a rudimentary model of Earth’s atmosphere that was loaded with assumptions. But it created such a stir that the preliminary nature of the research was obscured.

The theory was quickly exploited by both its critics and boosters--attacked on the one side as anti-nuclear propaganda but held up by the other side as an unsurvivable “doomsday scenario.”

As increasingly sophisticated computer simulations of the phenomenon have been run, the initial, catastrophic findings of the TTAPS group have been mitigated. For example, rather than long periods of subfreezing temperatures across entire continents, many scientists now predict spotty areas of quick frosts--”nuclear fall.”

But even the best of the models still must include substantial assumptions, almost every assumption having to do with smoke, said Harold Brode, a veteran fire physicist at Pacific-Sierra Research, which does fire research primarily for the Pentagon. Scientists are ignorant of many of the details of the physics and chemistry of combustion, Radke added.

One important question is how much smoke would be produced by nuclear-set fires. But that may be an unanswerable question because of circumstances that simply cannot be predicted.

For example, if the United States and the Soviet Union target each another’s missile silos, the resulting fires would mostly be wild prairie fires; but if the targets were shipyards and oil fields, the consequences for the atmosphere could be much worse, Turco said.

Local weather conditions also could significantly affect how much smoke is produced. On a hazy or rainy day, the pulse of light from a nuclear explosion would not travel as far, and so there would be fewer fires.

Smoke production also depends on the time of year. “In the Pacific Northwest you can drop hydrogen bombs on forests in December and all you’re going to do is scorch the needles,” said Radke, who teaches at the University of Washington in Seattle. “It’s wet out there.”

It is such unknowns that make any simulated effects of a nuclear winter open to question. For example, one recent series of computer simulations at the National Center for Atmospheric Research had to use estimates of smoke that ranged from 20 to 180 million tons.

Another unresolved question--but one that may be answered by the upcoming experimental fire--concerns the nature of the smoke that is produced by large fires and how it behaves in the atmosphere. For example, black sooty smoke, the kind created when oils and plastics burn, is more effective at blocking sunlight than the light smoke produced when a forest burns. Also, different types of smoke are removed from the atmosphere at different rates.

“This is the real crux of the nuclear winter question,” Brode said.

During the experimental fire, researchers will be watching for the possible formation of a capping cloud, a mushroom-shaped cloud of water droplets created when hot gusts from a fire rush up and clash with cold air.

Such a cloud would be considered a sign that large numbers of smoke particles will be removed from the atmosphere--thus letting more sunlight through.

Water Vapor Condensation

Researchers believe that a capping cloud is created by large smoke particles that can form “cloud condensation nuclei” that condense water vapor into droplets. These eventually fall as rain, thus somewhat reducing the density of the smoke cloud.

Small smoke particles, on the other hand, tend to stay aloft longer, although some types of small particles can collide and stick together, forming larger particles that eventually rain out.

The most recent work on “rain-out,” according to scientists at the National Center for Atmospheric Research, indicates that “even under ideal rain-out conditions, a substantial amount of smoke would probably remain in the atmosphere.” But Turco and others say that more data must be gathered on this phenomenon.

Smoke not only plays an important role in determining how much sunlight gets in but also determines how much heat can leave Earth.

Small particles block incoming sunlight but allow heat radiating from Earth to escape into space. “Fine particles of soot work like a one-way mirror,” Brode said.

If the upper atmosphere became filled with very fine soot, Earth’s surface would cool, while the air surrounding the smoke would be heated by the solar energy absorbed by the smoke particles. And because hot air rises, the smoky, heated air masses would likely linger.

Still another important variable that affects the nature and the fate of smoke produced in a nuclear war is the rate and intensity of the fires, Brode said.

He and other scientists surmise that most modern cities--filled with cement, steel, wood and plastic--would probably burn slowly, producing sputtering, cool flames and sooty smoke.

‘Scale of a Hibachi’

The reason that no one knows for sure is because experiments in the physics of fire and smoke have taken place primarily in the laboratory, mostly “at the scale of a hibachi,” Radke said. “It takes a lot of imagination to think that anything coming out of a small flame in a laboratory has anything to do with a big fire.”

Brode put the problem this way: “Even though things may have worked fine at the fireplace scale, that doesn’t mean things will work the same way in a forest fire. And you can be sure that in an urban conflagration there will be more physical processes hiding in the wings.”

Added Stephen Schneider, an atmospheric scientist at the National Center for Atmospheric Research and a proponent of the “nuclear fall” theory: “You can’t possibly extrapolate any conclusion from a small-scale fire to what would happen if cities burned.”

A year ago, leading atmospheric scientists observed a controlled burn in the Ontario wilderness to rid 1,600 acres of dead timber that had been infested with spruce budworm.

At the time, the Canadian fire was touted as the first major attempt to simulate a nuclear fire. But no instruments at all were deployed, according to Turco, who watched the blaze from a 100-foot tower about two miles away.

All he came away with, he said, were simple observations that proved nothing.

The upcoming fire in the San Gabriel Mountains originally was planned in 1984 as a management burn to create a barrier against future fires, Riggan said. But Forest Service officials realized that such a burn would provide a valuable opportunity for researchers--hence the delay to allow scientists to gear up.

Nuclear Studies Added

Most of the research projects initially proposed dealt with local concerns, such as air pollution, erosion and flood control, according to Riggan, who is now directing all the research involving the fire. The nuclear winter studies were added later.

Riggan said that even though the fire may take place in the heart of Southern California’s brush fire season, officials are confident that the burn will proceed safely.

Indeed such concern for safety means that the fire will not be ideal from the scientific standpoint. “We want to burn it as fast as possible and as hot as possible,” Turco said. “(But) they don’t want Los Angeles to go up in flames.”

That leaves officials with only one real worry: the arsonist.

They don’t want the fire to start before they are ready.

NUCLEAR WINTER: PUTTING A CONTROVERSIAL THEORY TO THE TEST The “nuclear winter” theory predicts that smoke from fires ignited by nuclear weapons could block out the sun, plunging Earth into cold and darkness. The hotly debated scenario will be put to its first test this fall when scientists set off a fire in the Angeles National Forest near Los Angeles. Many aircrafts, including a helicopter and a U-2 spy plane, will study the plume, expected to rise 10,000 feet or more. 1. Planes will take samples of smoke particles and look for any “capping cloud” that might form. Such clouds would contain water droplets, which would absorb smoke particles, thereby letting sunlight through.

2. A helicopter will gather samples of smoke and gas from just above the flame tops to provide data on how particles age, from the moment they are created.

3. The sampling aircraft will be equipped to detect whether smoke particles absorb or scatter light. If sunlight is scattered, much of it will still reach the Earth. The smoke will be monitored for up to two days.