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In a Summer of Fire, Is Warming a Cause?

August 27, 2000|Lewis MacAdams | Lewis MacAdams, a poet, is the founder and chairman of Friends of the Los Angeles River. His new book, "Birth of the Cool," will be published early next year

By the beginning of the year, analysts at the National Interagency Fire Center in Boise, Idaho, were nervous. All over the inter-mountain West, a slew of warm, wet El Nino winters had fed the growth of new trees and brush. Then came last winter's La Nina--cold and dry, with howling winds. The forest under-story was becoming the kind of fuel that can turn a small fire into a devastating inferno. The Fire Danger Index, which the Interagency Fire Center uses to estimate the likelihood of a fire being triggered by anything from a cigarette flipped out a car window to a lightning storm, was veering upward of 80%.

The first major blaze went off in February, scorching 40,000 acres of southeast New Mexico ranchlands. Three months, more than 70,000 fires and 5.8 million acres later, an area larger than New Hampshire has been seared, with the fire season still a long way from over. The epicenter of the fires has shifted north, to the Idaho-Montana border, where more than a million acres is burning out of control, and a pall of smoke has blanketed the land for a month. Backed by 65 air tankers, 225 helicopters and mountains of gigantic earthmoving machinery, 25,000 firefighters, augmented by crews from Australia, New Zealand, Canada and Mexico, have joined the battle, alongside elements of the U.S. Army, the National Guard and the Marines. By every measure, this is the worst fire season in 50 years.

Many factors add up to a forest or range fire: dry weather, strong winds, high temperatures. Ecologists would add industrial forestry and the rapidly growing urban population concentrated in our most arid states. Now scientists have begun to study another, more ominous possibility: global warming.

Everybody cautions that computer models aren't good enough yet to make predictions. "It's very difficult to say with a great degree of certainty," warns UC Berkeley Professor John Harte, who studies climate and its effect on the ecosystem, "but what you can say is that this summer's events are very typical of the kinds of phenomenon we would see more of during global warming." Ecosystem ecologist Janine Bloomfield of Environmental Defense in New York concurs. "This type of year is the kind of year you'd expect from climate change," she says.

Computer models project that a sustained increase of only 1 degree Celsius in global mean temperatures will cause changes in regional climates that will affect the ability of forests to grow and regenerate. The United Nations Intergovernmental Panel on Climate Change estimates that a 1 degree to 3.5 degree C heat increase over the next 100 years would adversely affect one-third of the world's remaining forests. According to a series of papers presented at a 1997 climate forum hosted by the White House Office of Science and Technology Policy, plants from the desert Southwest appear to be migrating north. Current biogeographical models indicate arid-land species are expanding into the Great Basin. By 2050, the Hadley Center for Climate Prediction and Research at the United Kingdom Meteorological Office predicts that huge blocks of Earth's remaining forest will die back, becoming grassland, steppe or desert.

Most forest fires are ignited by lightning. At any given moment, some 2,000 thunderstorms are in progress across the Earth's surface, and lightning strikes about 100 times each second--typically at higher altitudes. Timothy Ingalsbee, a PhD at the Western Fire Ecology Center in Eugene, Ore. states, "Global warming unsettles the weather." Unsettled weather, particularly in warm climates, is the ultimate cause of lightning.

When warm air bubbles up from the Earth's surface, it collides with cooler air from the upper atmosphere to produce the towering cumulonimbus clouds that become thunderstorms. But because this has been such a dry year, the clouds contain so little moisture they produce lightning without rain.

As the planet heats up, warmer climates expand north and south. Harte, speaking from a field station at the Rocky Mountains Biological Laboratory 10,000 feet up the western slope of the Rockies, explains that the differential between the earth's warmer surface and the cooler upper air will increase, leading to more violent weather. Earle R. Williams of the Massachusetts Institute of Technology suggests a relatively small increase in local temperatures produces a large increase in thunderstorm activity. A 1 degree C rise in the Earth's average temperature, according to researcher Colin Pierce of Columbia University, increases the potential for lighting by 10 kilovolts.

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