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May|June 2005
The Brains Behind Blackmun By David J. Garrow
Readers Respond: Justice Blackmun
Unbecoming Justice Blackmun By William Saletan
A Measure Of Truth By Kermit Roosevelt
The Federalist Capers By Roderick M. Hills, Jr.
A Dirty Little Secret By Eric Redman
Justice on the Half Shell By Aaron Kuriloff
The Prince of Darknet By Joseph D. Lasica

A Dirty Little Secret

Soot: The Carcinogenic, Climate-Changing Grime No One Talks About.

By Eric Redman

HUMANS CONTRIBUTE TO GLOBAL WARMING—scientifically, that's settled. But we rarely ask, by what means? We assume we know: Burning fossil fuels like coal, oil, and natural gas produces carbon dioxide (CO2), a "greenhouse gas" that traps heat in Earth's atmosphere. But that widely accepted hypothesis turns out to be seriously incomplete. So our CO2-focused climate policy and the layers of laws built on it—from European rules implementing the Kyoto Protocol to the United States regulations charging fees to new power plants for their CO2 emissions—are incomplete as well. That huge problem is partly driven by something tiny: the ultra-fine particles we know as soot.

Research papers on "black carbon" sometimes begin with a quotation from Bert, the London chimney sweep, in the movie Mary Poppins: "It's just good clean soot." The epigraph is meant ironically—soot is nasty stuff. A potent carcinogen, soot once caused widespread scrotal cancer among—who else?—London chimney sweeps. Soot also causes heart and lung disease. But today's soot researchers aren't writing about health. They're exploring global warming, an area of debate where activism and lawmaking can outstrip scientific understanding. Here at the noisy intersection of politics, law, and science, soot may perform a service: It could help change how policymakers think about global warming, and what they do about it.

THE IDEA THAT SOOT PLAYS A MAJOR ROLE IN GLOBAL WARMING burst upon the climate policy world in 2000, largely because of James Hansen, the head of NASA's Goddard Institute for Space Studies. Other scientists wrote about soot earlier. But Hansen, who sounded the alarm most forcefully in a paper published that year in Proceedings of the National Academy of Sciences, can fairly be described as soot's nemesis. Unfortunately, soot almost became his as well.

Hansen's message and its timing had drawbacks. The drafting of the Kyoto Protocol, which calls for major cuts in greenhouse gas emissions by Western nations, had been completed just three years earlier—with no provisions for soot or other pollutants. Kyoto exempts developing nations from emissions cuts completely. In 1992, when the Kyoto negotiations began, those nations used relatively little fossil fuel and produced correspondingly little CO2. But by 2000, when Hansen wrote, that had changed drastically. And developing nations produce most of the world's soot.

So when Hansen's paper gained attention outside the jargon-fortified walls of atmospheric science, his message that soot, not just CO2, helps drive global warming wasn't welcome among climatologists and activists, who wanted to keep the climate spotlight squarely on CO2 and the West. The political landscape made Hansen's message particularly worrisome. George W. Bush publicly rejected Kyoto, angering its drafters, environmentalists, and European leaders. Bush seemed to doubt the very notion of global warming, the climate impact of fossil fuels, and the policy of singling out Western nations for responsibility. Climate insiders feared that if soot were seen as playing a major role in global warming, Bush would seize upon it to justify his position.

Hansen's pronouncement came at an awkward moment—the moment Kyoto began to stall, its fate still uncertain. (Russia's ratification of Kyoto last year finally made the protocol effective.) And Hansen couldn't be ignored. He enjoyed immense stature as an early and effective proponent of the greenhouse gas theory of global warming. "In some respects, he's the father of the whole concept," said John Thompson, national advocacy coordinator for the Boston-based nonprofit Clean Air Task Force. "He's almost revered." While the mechanism of global warming was discovered in the 19th century, it took Hansen's 1982 Congressional testimony to bring it out of the laboratory and into rooms where people thrust microphones and pound gavels. Hansen didn't do it alone, yet he did lead the effort, and very visibly. How could he suddenly divert attention from CO2 to soot?

Fiercely committed to his science, Hansen perhaps displayed a certain moth-to-the-flame incaution. Just as he once needed to persuade the world about greenhouse gases, he now needed to persuade the world about soot and other non-CO2 pollutants, even though doing so meant some colleagues and environmentalists would vilify him. Nature magazine let others challenge his work, but wouldn't publish Hansen's response in a form he considered acceptable (he ultimately defended himself in an open letter circulated by e-mail). A November 2000 article by Richard Monastersky in The Chronicle of Higher Education quoted one scientist who called Hansen "naïve," another who termed his article "a con trick," and a Sierra Club representative who basically accused Hansen of aiding and abetting the enemy. Confirming the critics' worst fears, Bush actually did start to invoke Hansen's theory in one presidential debate with Al Gore—just as the moderator called "Time."

Even Hansen's close allies, like advocacy groups working to cut emissions from coal plants, didn't know what to do. They agonized about calling attention to the third world and its soot. They fretted about scientific uncertainty and about overstating soot's role. They worried about backlash from CO2-obsessed allies and funding sources. They worried about perceived apostasy and about playing into Bush's hands.

So for four years after 2000—as long as George W. Bush remained a candidate for re-election—few climate policymakers and environmental activists endorsed Hansen's soot argument. A generation earlier, Hansen had captivated the world by explaining the greenhouse effect. When it came to soot, folks either scowled or shrugged and then went back to talking about CO2.

Hansen never recanted. He was almost certainly right, as later research showed. But by 2004, when Hansen publicly chided the Bush Administration on science matters during the presidential campaign (another display of incaution, since Hansen was a NASA employee), a typical article by Hansen and colleagues emphasized an important qualification: "The substantial role inferred for soot in global climate does not alter the fact that greenhouse gases are the primary cause of global warming in the past century and are expected to be the largest [cause for] the rest of this century."

Hansen also writes about more than just soot. He focuses on neglected greenhouse gases like methane—which is 20 times more potent than CO2 as a global warmer, not in total but ounce for ounce—and other pollutants. But a typical Hansen article doesn't step back much from the challenge he first posed five years ago. He still argues that a quarter of observed global warming comes from just one of soot's impacts: its darkening of ice and snow (white surfaces reflect solar energy back to space; dirty ones don't). And, he asserts, the total warming impact of soot, plus methane and one form of ozone, may actually exceed that of CO2.

SOOT AND CO2 ARE CARBON COUSINS, both coughed up from burning, regardless of the fuel source. Because soot is never produced without CO2 being produced as well, when Hansen drew attention to the role of soot in global warming, some observers pooh-poohed its significance. Control the CO2, they said, and you'll control the soot.

But although CO2 and soot are born together, they differ in key respects. CO2 is fully burned carbon, the product of complete combustion. Soot is carbon that's partly burned, the product of incomplete combustion. In Western nations, most carbon gets burned completely. That efficiency, plus the West's prodigious appetite for fossil fuels, explains why the West produces so much CO2 and relatively little soot. The fuels on which the West relies make a difference, too: Gasoline gets burned efficiently, producing CO2 but not much soot.

In China, India, and the developing world generally, the situation is reversed: Fuel use is hugely inefficient, so its reincarnation as soot, not CO2, becomes the destiny of staggering amounts of carbon, whether it originates in coal, diesel fuel, firewood, or camel dung. Non-Western nations also depend on inherently sooty fuels. Most of the world's soot now comes from burning biomass. Half is from open burning of fields and forests. Thirty percent comes from residential use of coal, firewood, and dung. Ten percent comes from diesel vehicles. As a result, while the gas-guzzling but cleaner-burning West has cut soot production drastically, soot emissions from rapidly industrializing China and India have doubled since 1970. To tackle soot, policymakers must move way beyond Kyoto's focus on the West.

Although born together in fire, CO2 and soot become separated at birth and live largely independent lives. This, too, has major policy implications. CO2, a gas, heads straight for the atmosphere and resides there for decades, even centuries, before being recycled in vegetation or the sea. That's why the warming impact of CO2, once airborne, is so persistent, and why more CO2-driven warming is inevitable. Of course, reducing CO2 emissions today will help limit global warming eventually. But the response time won't be quick.

Soot, although formed in fine particles that float up into the air, remains for all its airiness an essentially earth-bound solid, like its heavier sibling, ash. It doesn't dwell long in the atmosphere. By CO2 standards, soot settles out almost at once—in hours, days, weeks. This means that controlling soot, unlike controlling CO2, could have a large effect immediately. Soot already aloft won't linger there, so cutting soot production could yield climate and health benefits right away.

This startling realization warrants pause, because controlling soot isn't on the agendas of climate policymakers or activists. As they have for decades, lawmakers and environmental advocates remain focused on CO2.

HANSEN AND OTHERS CALCULATE THAT SOOT accounts for more than a quarter of all observed global warming. In combination with other pollutants such as methane, it accounts for at least as much warming as CO2. As with all pollutants, including CO2, there's a "plus or minus" band around such estimates, so soot's contribution could actually be somewhat less—or more.

Soot's warming impact, like that of CO2, remains simpler to describe than to quantify. The effect of soot lying on the ground is easiest to understand. Because soot is dark, it absorbs sunlight instead of reflecting it back to space, thus heating the surfaces on which soot falls. This ground-level warming is producing alarming effects in the Arctic, on mountain peaks, and in other lands of ice and snow. News accounts of thinning ice and melting glaciers may have less to do with climate than with this localized soot-driven thawing. In other words, even apart from its global warming impacts, soot melts ice and snow directly. In China and Tibet, where clouds of hazy soot from India press up against the Himalayas, glaciers are now retreating rapidly in a region that's apparently growing colder.

Soot sullying the naturally reflective and earth-cooling Arctic and melting it seems particularly worrisome. (Global wind patterns aren't symmetrical, so less soot falls on Antarctica.) The Arctic produces little soot itself, of course; its soot arrives from abroad. Soot's direct thawing impact makes the Arctic a double victim, since one feature of global warming is that it typically produces twice the temperature hit in high latitudes as it does worldwide. That's one reason scientists prefer the term "climate change" to "global warming": although warming is measured as an increase in average global temperatures, its actual impacts are unevenly distributed.

Soot is unevenly distributed, too. It concentrates itself in plumes, rising from distinct sources—a tailpipe, a fire, a furnace or stove—venturing aloft, then settling back to earth. It never mixes evenly in the atmosphere. Soot's trajectory may carry it a few feet or to Alaska, a mile downwind or across an ocean. (The United States' West Coast apparently owes its increasingly vivid sunsets to soot from China, which also supplies a lot to faraway Greenland.) The global impact of a pollutant that behaves this way is tough to model.

Another complication is that a different product of incomplete combustion—organic carbon, a white constituent of smoke—has the opposite effect of soot, reflecting sunlight back to space. This reduces soot's warming impact, but no one knows by how much. Every source of soot, every fuel and means of burning it, has its own ratio of soot to organic carbon; few have yet been analyzed. "We don't even know," said Clean Air Task Force's executive director Armond Cohen, "exactly what comes out of a diesel tailpipe." Few people are trained to analyze what drifts up from New England chimneys, let alone the smoky vortex of a slash-burned tropical forest in Southeast Asia.

These complexities and uncertainties don't give soot a pass; it's still a climate warmer, and, unlike CO2, it makes people sick. More soot research is needed, but science already can tell us this: Although soot may not constitute the sum total of everything important yet unaddressed in climate policy, soot does indicate what's wrong. Years ago, thanks to Hansen and others, scientists recognized that CO2 warms the atmosphere. Climate treaties, laws, and regulations were then written, as a practical matter, to address this one pollutant almost exclusively. So current law and policy, public perceptions of global warming, and the coming drive for Congressional enactment of new CO2 taxes still reflect a half-truth: the notion that CO2 alone is the problem, and that nothing else much matters.

THE EARTH WARMS AND COOLS NATURALLY, in long and somewhat irregular cycles. That explains ice ages, and why, conversely, lions once roamed England's Salisbury Plain. At the moment, judging by the past, the planet is approaching a warming peak. It's not as warm (yet) as prior peaks, including the most recent one, and today's warming definitely has natural causes (an apparent cyclical increase in solar energy reaching the Earth) as well as human ones. The significance of human-caused greenhouse gases—particularly CO2, with its great longevity in the atmosphere—is that they "lock in" the warming trend for a long time to come.

No one wishes another ice age on our descendants. But neither do we wish them rising sea levels, widespread coastal flooding, and destruction of the Arctic environment—all of which scientists can confidently predict if the United States and other nations don't act now to check the increments of warming that human activity adds to the atmosphere.

The policy issue is what precisely "act now" should imply. Perhaps it made sense to concentrate on reducing CO2 emissions first, given CO2's prevalence and potency, and because early models of the atmosphere were too crude to reveal the role of non-CO2 pollutants in the climate equation. But today, knowledge about climate change is more sophisticated, and the meaning of "act now" should be as well.

What Hansen and his colleagues urge is not that policymakers forget about CO2 but that they buy more time to deal with it. In addition to controlling CO2, both Western and non-Western nations should adopt new laws and policies (and target foreign aid and investment) to reduce emissions of soot and other pollutants—pollutants that are potent warmers, cheaper than CO2 to control, and collectively as important as CO2. By doing this quickly, Hansen argues, policymakers can flatten the rising world temperature curve and help assure a lower ultimate peak temperature—plus save the Arctic and aid human health.

One reason to buy time is that it yields technological progress. (That's why the streets of New York escaped eventual immersion in horse manure as the city's population grew: someone invented cars.) Technological progress is almost certainly the key to reducing CO2 emissions without reducing human income, wealth, and conventional measures of well-being. Because CO2 comes from carbon that's already being burned efficiently, in order to put less into the atmosphere without reducing income or wealth we need either cost-effective substitutes for burning carbon or ways to store CO2 geologically and in vegetation. Time (and wealth) can buy us both.

The horizon is filled with promising, carbon-sparing new energy technologies. Wind and solar power alone can't fully substitute for fossil fuels. But a CO2-limiting energy strategy can be constructed from many parts. These include coal gasification (the process of transforming coal into gas for fuel use, which reduces CO2 per unit of energy produced), other forms of renewable energy, and, ultimately, fuel cells and other applications of the "hydrogen economy." Energy conservation throughout the West continues to advance rapidly, along with high-tech means to store CO2, thus reducing the amount that reaches the atmosphere.

But not all the needed technology is high-tech. And not all the climate-protecting dollars should be spent at home. It's important to remember how much of the world's carbon is burned inefficiently, without effective emission controls, yielding the dirty haze of soot and other pollutants that hangs over what used to be called the third world. What the world needs now includes small, inexpensive, clean-burning residential stoves. Western dollars could put one in every non-Western home. In both climate and health terms, it would be money well spent.

If governments and the activists who prod them are serious about limiting the human contribution to global warming, it's necessary to face east and tackle warming agents besides just CO2. Fortunately, as Hansen points out, there's a good example to guide this effort. In 1985, observation confirmed what science had predicted: a thinning of the ozone layer above the Earth, the result of human-produced chlorofluorocarbons (CFCs) reaching the stratosphere, changing to chlorine, and gobbling up the ozone. The world reacted almost instantly, not for climate reasons but to prevent sharp increases in skin cancer (the ozone layer limits ultraviolet rays). The West not only banned CFCs—used for refrigerator coolant and in spray cans—and found substitutes for them, but it also bought out CFC production in China and India by spending hundreds of millions of dollars for facilities to produce the substitutes.

In the current economic circumstances—with the West losing jobs and production of goods to the East—the notion of paying China, India, and other developing nations to use energy more efficiently and cut emissions of CO2, soot, and other climate warmers may prove politically galling as well as expensive. Critics might argue that the United States and other Western nations should tend their own gardens first. But if little is done beyond pruning CO2 emissions in the West, those gardens will grow ever warmer. And, thanks to long winds and relentless gravity, thicker with foreign soot.

Eric Redman is a lawyer with the firm of Heller Ehrman and the author of The Dance of Legislation.

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