Domingo 11 de Enero de 2009

Dark green
Por Drake Bennett

When we look at nature, it has become commonplace to see a fastidiously self-regulating system at work: wildebeest trim the savannah grasses, lions cull the wildebeest herds, and vultures clean the bones of both. Forests take in the carbon dioxide we exhale, use it to grow, and replace it with oxygen. The planet even has a thermostat, the carbon cycle, which relies on the interplay of volcanoes, rain, sunlight, plants, and plankton to keep the earth's temperature in a range congenial to life.

This idea of nature's harmonious balance has become not just the bedrock of environmental thought, but a driving force in policy and culture. It is the sentiment behind Henry David Thoreau's dictum, "In wildness is the preservation of the world." It lies behind last summer's animated blockbuster "Wall-E," in which a single surviving plant helps revive an earth smothered beneath the detritus of human overconsumption. It underlies environmental laws that try to minimize the damaging influence of humans on land and the atmosphere.

In this line of thought, the workings of the natural world, honed over billions of years of evolution, have reached a dynamic equilibrium far more elegant - and ultimately durable - than the clumsy attempts humankind makes to alter or improve them.

According to the paleontologist Peter Ward, however, nothing could be further from the truth. In his view, the earth's history makes clear that, left to run its course, life isn't naturally nourishing - it's poisonous. Rather than a supple system of checks and balances, he argues, the natural world is a doomsday device careening from one cataclysm to another. Long before humans came onto the scene, primitive life forms were busily trashing the planet, and on multiple occasions, Ward argues, they came close to rendering it lifeless. Around 3.7 billion years ago, they created a planet-girdling methane smog that threatened to extinguish every living thing; a little over a billion years later they pumped the atmosphere full of poison gas. (That gas, ironically, was oxygen, which later life forms adapted to use as fuel.)

The story of life on earth, in Ward's reckoning, is a long series of suicide attempts. Four of the five major mass extinctions since the rise of animals, Ward says, were caused not by meteor impacts or volcanic eruptions, but by bacteria, and twice, he argues, the planet was transformed into a nearly total ball of ice thanks to the voracious appetites of plants. In other words, it's not just human beings, with our chemical spills, nuclear arsenals, and tailpipe emissions, who are a menace. The main threat to life is life itself.

"Life is toxic," Ward says. "It's life that's causing all the damn problems."

Ward, a paleontologist at the University of Washington and a scholar of the earth's great extinctions, calls his model the Medea Hypothesis, after the mythological Greek sorceress who killed her own children. The name makes clear Ward's ambition: To challenge and eventually replace the Gaia Hypothesis, the well-known 1970s scientific model that posits that every living thing on earth is part of a gargantuan, self-regulating super-organism.

Ward holds the Gaia Hypothesis, and the thinking behind it, responsible for encouraging a set of fairy-tale assumptions about the earth, and he'd like his new book, due out this spring, to help puncture them. He hopes not only to shake the philosophical underpinnings of environmentalism, but to reshape our understanding of our relationship with nature, and of life's ultimate sustainability on this planet and beyond.

Although Ward's ideas have yet to reach a broad audience, some scientists are welcoming his portrait of a constantly off-kilter earth as a corrective to the gauzier precepts that have cast their spells on environmental philosophy and policy. Others, however, describe his hypothesis as simply Gaia's dark twin, a model undermined by the same inclination to see one tendency as the whole story. Ward is open to the criticism that he's taken things too far; what's important, he believes, is weaning people from the idea that the earth works better without us. Even if Medea is an incomplete framework for viewing the natural world, it introduces a hardheadedness into environmental debates often driven by an unexamined idealism about Mother Nature.

Ward himself believes that the only help for the planet over the long run is management by human beings - whether that means actively adjusting the chemical composition of the atmosphere or using giant satellites to modify the amount of sunlight that reaches us. As Ward sees it, the planet doesn't need our help destroying itself. It will do that automatically. It needs us to save it.

For most of human history, it would have been alien to think of the planet as a "system" at all - the earth seemed an essentially infinite expanse of lands and seas that, depending on your theology, awaited human cultivation or demanded human deference. But with the Industrial Revolution it started to become clear that humans themselves were making changes with far-reaching, unintended, and destructive consequences, and over the 20th century an alternative understanding of the natural world began to take hold. This view saw the earth as a closed system with an inherent natural order, and pointed out the ways it broke down when we stressed it by pumping chemicals into the air or killing off animals that were vital links in food chains.

By the late 1970s, when the British scientist James Lovelock proposed the Gaia Hypothesis, something that once might have seemed like science fiction - the notion that all living things on the planet were linked like the cells in a single body - seemed like a persuasive model.

Lovelock was a serious scientist - a creation of his, the electron capture detector, was to prove instrumental in revealing the depletion of the ozone layer - and he had plenty of evidence for his theory. He pointed to the fact that, despite the wide variability of the sun's heat over the eons, microbes and plants have altered both the atmosphere and the ground to keep the temperature almost entirely within the narrow range in which terrestrial life thrives. For nearly as long, the amount of oxygen that plants and geological processes released into the atmosphere has remained at a point high enough to feed the metabolisms of quintillions of animals, but not so high that every forest was constantly going up in flames.

In the Gaian model, the world is maintained by an interlocking feedback system that puts a brake on drastic changes. Lovelock pointed to the role that plants play in the carbon cycle's planetary thermostat: When the planet warms, forests and phytoplankton suck carbon dioxide out of the air at a faster rate and create sheltering layers of clouds, both of which work to cool the planet. In a more familiar example from the animal kingdom, populations of predator and prey limit each other's sizes.

While the Gaia Hypothesis may be the most explicit version, the idea of a self-regulating, counterpoised planet has been central to the thinking of conservationists and environmentalists, and to the policies they have helped to shape. Removing dams, fighting the encroachment of alien plant and animal species, restoring the Everglades, reintroducing wolves into the American West, all are justified at least partly because they help restore a balance that man has disturbed.

As Ward sees it, however, this is almost exactly backward. Looking at the evidence of past extinctions - written in fossils and in the chemical makeup of deeply buried rock sediments - as well as the workings of today's oceans, atmosphere, and myriad food chains, he finds evidence of a planet that tends not toward harmony but toward extremes. Although windows of stability are possible, they are simply respites between catastrophic boom-and-bust cycles. He attributes one of the largest extinctions in history to the out-of-control proliferation of plankton feeding on upwellings of nutrients from the ocean floor. Rather than being elegantly brought back to equilibrium, the tiny organisms reproduced until they choked off much of the life in the upper ocean. Exhausting their newfound food supply, they died en masse, and decaying by the trillions used up all the oxygen in the water, killing off everything else.

As for the earth's temperature control, Ward, drawing on the writing of the environmental scientist James Kirchner, points out that more often than not the thermostat seems to be hooked up backward, with warming triggering more warming, and cooling more cooling. In a process we're seeing today, as the planetary temperature rises, warming increases the rate at which soil releases greenhouse gases - not only carbon dioxide, but methane and nitrous oxide. It leads to more forest growth in places that formerly were barren tundra, even as more carbon dioxide in the air makes plants hardier and better able to grow in areas once given over to desert. More plants in more places means a darker earth, and therefore a more heat-absorbent and warmer one. It's an escalating feedback loop that becomes even more powerful as the planet's white, ice-covered poles give way to darker open water.

The dangerous positive feedback can run the other way, too, Ward argues. He blames a planetary glut of plant life for the two prehistoric "snowball earth" episodes, 2.3 billion and 700 million years ago, when the planet froze from pole to pole. In a reverse greenhouse effect, the earth's plants, photosynthesizing madly, sucked so much carbon dioxide out of the air that temperatures plunged. Far from nurturing life, the world's plants nearly froze it to death.

Although Ward is a leading expert on the Cretaceous-Tertiary extinction (the one, 65 million years ago, that killed off the last of the dinosaurs), his reputation in recent years has been as a writer of popular science books - his best known, "Rare Earth," is an argument against the likelihood of complex life being found elsewhere in the universe, coauthored in 2000 with the astronomer Donald Brownlee. Ward hopes the forthcoming book will find a wide readership, but also intends it as a serious theoretical framework for research into the interplay between living things and their environment.

So far, since Ward has not presented the Medea Hypothesis in papers or at conferences, it remains relatively unknown to environmental researchers and earth scientists. But among those familiar with it, there is a sense that its focus on nature's lethal erraticism could shape the debate, both in and out of academe, over the planet's long-term prospects.

"I think that it's a very valuable contribution to be focusing on the very serious destabilizing effects of life," says David Schwartzman, a professor at Howard University who reviewed a draft of Ward's book. Schwartzman's field, biogeochemistry, grew to prominence largely out of arguments over the Gaia Hypothesis. "There's no a priori reason to think that life's feedback with the environment necessarily is stabilizing."

"We do tend to think about everything being coordinated and helping each other," says Tyler Volk, an earth systems scientist at New York University and author of the book "CO2 Rising." "I basically agree with Ward that organisms can come along and create conditions that make it very difficult for a lot of other species."

But Schwartzman and Volk, among others, also caution that Medea may be as incomplete a model in its way as Gaia is. Since the late 1970s, even prominent Gaian thinkers such as Lovelock have moderated some of their stronger claims: They no longer describe the biosphere as a single organism, and they concede that not all the planet's feedback loops tend toward stability.

In fact, most earth scientists see no need to choose between Gaia and Medea: The earth, naturally, is a bit of both. "The natural world is an interestingly complex place," says Kirchner, director of the Swiss Federal Institute for Forest, Snow and Landscape Research.

Stephen Schneider, a climatologist at Stanford University, is more dismissive. "Anybody who tells you [the feedbacks] are all positive or all negative is writing a potboiler," he says.

Other scientists take issue with Ward's reading of the prehistoric record, suggesting he may be blaming early life forms for catastrophes they did not cause. In the field of paleontology, some of the fiercest arguments of recent decades have been over what caused prehistory's great die-offs, and Ward has been in the middle of a few of those arguments. There's still significant debate, for example, over whether living things actually caused the Great Oxidation Event (and ensuing extinction) 2.5 billion years ago, and whether plants and other organisms can really be blamed for the "snowball earth" deep freezes and some of the more recent mass extinctions.

Ward cheerfully concedes that he may be proven at least partly wrong.

"I'm just erecting a series of hypotheses - some are going to turn out to be true," he predicts. "But there is nothing else to balance Gaia, there's nothing else for people to take a swat at. I welcome that. I have thick skin."

At the very least, Ward hopes to shape the image of the earth in the public imagination, and by extension in public policy. Beneath much environmental regulation lies the basically Gaian belief that, when faced with a brewing global problem like climate change, our best response should be to try as much as possible to take ourselves out of the equation, to reduce our carbon emissions to the point where we're no longer a factor in the feedback loops. Trying instead to manage something as hopelessly complex as the climate is seen as an act of Frankensteinian hubris.

Ward, however, argues that this way of seeing things only makes sense if one assumes that the earth will, once righted, inevitably return to the set of conditions most suitable for our continued survival. History, he argues, suggests it very well may not. Faced with a planet where life is almost guaranteed to wipe itself out - and take us with it - he is urging us to be active, and occasionally intrusive, guardians.

To combat climate change, Ward sees that role including engineering projects on a previously unimaginable scale, like cooling the atmosphere by seeding it with sulfuric acid or installing giant shields in space to deflect away sunlight. As the scientific consensus around climate change has spread and hardened, these so-called "geoengineering" projects have received more of a hearing, but most climate and earth scientists remain skeptical because of the enormous uncertainties about what their full effects would be.

Ironically, Lovelock himself has also, in the last few years, become an advocate for a geoengineering fix for climate change - specifically, an armada of vertical pipes placed in the oceans to bring colder, nutrient-rich water to the surface to absorb more carbon out of the air. But while Lovelock has described his proposal as an "emergency treatment" for a critically ill planet, Ward believes such schemes are going to have to become business as usual if we and our descendants are going to survive.

"The longevity of the biosphere can only be sustained through large-scale geoengineering," Ward argues. Without our firm hand, he believes, "the earth will go to hell in a handbasket," just as it has again and again in the past.