The Best American Science and Nature Writing Part 9

That's not the only way birds cope with human noise. In 2007 Richard Fuller and two other scientists at the University of Sheffield in the United Kingdom discovered that European robins liv ing in noisy urban areas have radically departed from their normal behavior of singing during the day. Now they sing almost exclusively at night, presumably to evade interference from the human din. If you hear a bird singing on your way home from a night at the pub, it's probably a robin, Fuller says.

In Berlin, nightingales have taken a different approach, raising their singing volume in response to traffic noise, according to a study by Henrik Brumm of that city's Free University, published in the Journal of Animal Ecology. In what is known as the Lombard effect, where a singer or speaker raises his voice to be heard, the nightingales try to counteract rush-hour clamor by singing louder on weekday mornings than on weekend mornings.

Most research on the impact of human sounds has focused on birds, but there is growing evidence that what's happening in the avian world is playing out across the animal kingdom, even in remote places that might seem impervious to human soundsa"places like the deep ocean.

Cities are getting louder, but underwater noise is increasing even faster. There are about twice as many ships plying the world's oceans now as in the 1960s, and these ships are faster, more powerful, and collectively far noisier than their predecessors. When scientists at the Scripps Inst.i.tution of Oceanography and the Colorado-based company Whale Acoustics compared sound levels west of California's San Nicolas Island in 2003 and 2004 with measurements made during the 1960s at the same site, they found that ambient noise levels had increased about tenfold. And this area may be representative of the entire northeast Pacific, the scientists say in a report published in the Journal of the Acoustical Society of America.

Instead of containing this noise within shipping lanes or coastal areas, the ocean's unique dynamics actually help the sounds travel hundreds or even thousands of kilometers. The so-called "deep sound channel" is a layer of water where sound travels slowly but encounters little resistance or interference. Some scientists suspect that humpback whales dive down to this channel and then sing into it, communicating with other humpbacks hundreds of kilometers away. And when noises from commercial shipping, offsh.o.r.e drilling, and other human activities get caught in the channel, they too are carried far from the original source.

Researchers have only just begun investigating these sounds' exact impacts, but a few studies suggest man-made noise is forcing marine mammals to respond in much the same way as birds do. Scientists at the Inst.i.tute of Ocean Sciences in Sidney, Canada, have shown that beluga whales change their vocal patterns in response to the presence of icebreakers, whose systems interfere with the belugas' preferred frequencies. Belugas also switch the frequencies of their echolocation clicks when background noise increases. Elsewhere, orcas in the Pacific Northwest have changed their calls, perhaps in response to increased traffic by commercial ships and whale-watching boats.

In more extreme cases, human sounds have forced whales to abandon their preferred habitat. For instance, gray whales have long used Baja California's Guerrero Negro lagoon as a calving ground. But when construction at a nearby salt factory spurred increases in ship traffic and dredging activities, the whales stayed away from the lagoon for several years, returning only after construction ebbed.

Some researchers interpret these adaptations as a heartening sign, pointing out that some animals will simply change along with the soundscape. But Slabbekoorn cautions that some species could be wiped out by the human din.

Because low-frequency traffic noise accounts for most of humans' clamor, animals that use low-frequency calls and can't switch to higher frequencies are threatened most. Slabbekoorn says birds such as orioles, great reed warblers, and house sparrows fit this category. Populations of house sparrows are declining throughout Europe; researchers haven't pinpointed the cause, but Slabbekoorn suspects human noise is a factor.

Bernie Krause has witnessed a similar phenomenon among spadefoot toads in the Mono Lake basin east of Yosemite National Park. Using its big front claws, the toad buries itself one meter below the desert floor and can survive there for up to six years. When rain finally comes, the toad emerges and joins others to sing in chorus, which makes it harder for predators such as owls and coyotes to get a bead on where the sound is coming from.

The problem is that during nighttime periods when the toads do their singing, military jet planes often use the basin for training. Flying only one hundred meters above the ground, the planes are so loud that the toads can't hear each other. Even after the planes leave, it takes twenty to forty-five minutes for the toads to resume their synchronized chorus, and in the meantime they're vulnerable to predators. Krause believes the noise is partly responsible for a precipitous decline in spadefoot populations, which he has studied since 1984.

Even adaptable species may be altered in fundamental ways. For instance, if changing calls or switching frequencies helps male birds be heard, they could earn an advantage when it comes to attracting female mates. Over time, this dynamic could force evolutionary changes, splitting populations of birds into localized species with specialized reactions to the sounds in their vicinity.

Slabbekoorn and his colleague Erwin Ripmeester think these noise-driven evolutionary forces may already be separating European blackbirds into urban and rural subspecies. The two researchers have even begun testing whether rural birds can recognize their urban brethren's hip new calls. If Slabbekoorn and Ripmeester's hunch is correct, it could mean that humans, already powerful conductors of the material world, may be extending their fierce control to the audible one.

ELIZABETH KOLBERT The Catastrophist.

FROM The New Yorker.

A FEW MONTHS AGO, James Hansen, the director of NASA's G.o.ddard Inst.i.tute for s.p.a.ce Studies, in Manhattan, took a day off from work to join a protest in Washington, D.C. The immediate target of the protest was the Capitol Power Plant, which supplies steam and chilled water to congressional offices, but more generally its object was coal, which is the world's leading source of greenhouse-gas emissions. As it happened, on the day of the protest it snowed. Hansen was wearing a trench coat and a wide-brimmed canvas boater. He had forgotten to bring gloves. His sister, who lives in D.C. and had come along to watch over him, told him that he looked like Indiana Jones.

The march to the power plant was to begin on Capitol Hill, at the Spirit of Justice Park. By the time Hansen arrived, thousands of protesters were already milling around, wearing green hard hats and carrying posters with messages like POWER PAST COAL and CLEAN COAL IS LIKE DRY WATER. Hansen was immediately surrounded by TV cameras.

"You are one of the preeminent climatologists in the world," one television reporter said. "How does this square with your science?"

"I'm trying to make clear what the connection is between the science and the policy," Hansen responded. "Somebody has to do it."

The reporter wasn't satisfied. "Civil disobedience?" he asked, in a tone of mock incredulity. Hansen said that he couldn't let young people put themselves on the line "and then I stand back behind them."

The reporter still hadn't got what he wanted: "We've heard that you all are planning, even hoping, to get arrested today. Is that true?"

"I wouldn't hope," Hansen said. "But I do want to draw attention to the issue, whatever is necessary to do that."

Hansen, who is sixty-eight, has greenish eyes, spa.r.s.e brown hair, and the distracted manner of a man who's just lost his wallet. (In fact, he frequently misplaces things, including, on occasion, his car.) Thirty years ago, he created one of the world's first climate models, nicknamed Model Zero, which he used to predict most of what has happened to the climate since. Sometimes he is referred to as the "father of global warming," and sometimes as the grandfather.

Hansen has now concluded, partly on the basis of his latest modeling efforts and partly on the basis of observations made by other scientists, that the threat of global warming is far greater than even he had suspected. Carbon dioxide isn't just approaching dangerous levels; it is already there. Unless immediate action is takena"including the shutdown of all the world's coal plants within the next two decadesa"the planet will be committed to change on a scale society won't be able to cope with. "This particular problem has become an emergency," Hansen said.

Hansen's revised calculations have prompted him to engage in activitiesa"like marching on Washingtona"that aging government scientists don't usually go in for. Last September, he traveled to England to testify on behalf of anticoal activists who were arrested while climbing the smokestack of a power station to spray-paint a message to the prime minister. (They were acquitted.) Speaking before a congressional special committee last year, Hansen a.s.serted that fossil fuel companies were knowingly spreading misinformation about global warming and that their chairmen "should be tried for high crimes against humanity and nature." He has compared freight trains carrying coal to "death trains," and he wrote to the head of the National Mining a.s.sociation, who sent him a letter of complaint, that if the comparison "makes you uncomfortable, well, perhaps it should."

Hansen insists that his intent is not to be provocative but conservative: his only aim is to preserve the world as we know it. "The science is clear," he said, when it was his turn to address the protesters blocking the entrance to the Capitol Power Plant. "This is our one chance."

The fifth of seven children, Hansen grew up in Denison, Iowa, a small, sleepy town close to the western edge of the state. His father was a tenant farmer who, after World War II, went to work as a bartender. All the kids slept in two rooms. As soon as he was old enough, Hansen went to work, too, delivering the Omaha World-Herald. When he was eighteen, he received a scholarship to attend the University of Iowa. It didn't cover housing, so he rented a room for twenty-five dollars a month and ate mostly cereal. He stayed on at the university to get a Ph.D. in physics, writing his dissertation on the atmosphere of Venus. From there he went directly to the G.o.ddard Inst.i.tute for s.p.a.ce Studiesa"GISS, for shorta"where he took up the study of Venusian clouds.

By all accounts, including his own, Hansen was preoccupied by his research and not much interested in anything else. GISS's offices are a few blocks south of Columbia University; when riots shut down the campus, in 1968, he barely noticed. At that point, GISS's computer was the fastest in the world, but it still had to be fed punch cards. "I was staying here late every night, reading in my decks of cards," Hansen recalled. In 1969 he left GISS for six months to study in the Netherlands. There he met his wife, Anniek, who is Dutch; the couple honeymooned in Florida, near Cape Canaveral, so they could watch an Apollo launch.

In 1973 the first Pioneer Venus mission was announced, and Hansen began designing an instrumenta"a polarimetera"to be carried on the orbiter. But soon his research interests began to shift earthward. A trio of chemistsa"they would later share a n.o.bel Prizea"had discovered that chlorofluorocarbons and other man-made chemicals could break down the ozone layer. It had also become clear that greenhouse gases were rapidly building up in the atmosphere.

"We realized that we had a planet that was changing before our eyes, and that's more interesting," Hansen told me. The topic attracted him for much the same reason Venus's clouds had: there were new research questions to be answered. He decided to try to adapt a computer program that had been designed to forecast the weather to see if it could be used to look further into the future. What would happen to Earth if, for example, greenhouse-gas levels were to double?

"He never worked on any topic thinking it might be any use for the world," Anniek told me. "He just wanted to figure out the scientific meaning of it."

When Hansen began his modeling work, there were good theoretical reasons for believing that increasing CO2 levels would cause the world to warm, but little empirical evidence. Average global temperatures had risen in the 1930s and '40s; then they had declined, in some regions, in the 1950s and '60s. A few years into his project, Hansen concluded that a new pattern was about to emerge. In 1981 he became the director of GISS. In a paper published that year in Science, he forecast that the following decade would be unusually warm. (That turned out to be the case.) In the same paper, he predicted that the 1990s would be warmer still. (That also turned out to be true.) Finally, he forecast that by the end of the twentieth century a global-warming signal would emerge from the "noise" of natural climate variability. (This, too, proved to be correct.) Later, Hansen became even more specific. In 1990 he bet a roomful of scientists that that year or one of the following two would be the warmest on record. (Within nine months, he had won the bet.) In 1991 he predicted that owing to the eruption of Mt. Pinatubo, in the Philippines, average global temperatures would drop and then, a few years later, recommence their upward climb, which was precisely what happened.

From early on, the significance of Hansen's insights was recognized by the scientific community. "The work that he did in the seventies, eighties, and nineties was absolutely groundbreaking," Spencer Weart, a physicist turned historian who has studied the efforts to understand climate change, told me. He added, "It does help to be right."

"I have a whole folder in my drawer labeled 'Canonical Papers,'" Michael Oppenheimer, a climate scientist at Princeton, said. "About half of them are Jim's."

Because of its implications for humanity, Hansen's work also attracted considerable attention from the world at large. His 1981 paper prompted the first front-page article on climate change that ran in the Timesa"STUDY FINDS WARMING TREND THAT COULD RAISE SEA LEVELS, the headline reada"and within a few years he was regularly being invited to testify before Congress. Still, Hansen says, he didn't imagine himself playing any role besides that of a research scientist. He is, he has written, "a poor communicator" and "not tactful."

"He's very shy," Ralph Cicerone, the president of the National Academy of Sciences, who has known Hansen for nearly forty years, told me. "And, as far as I can tell, he does not enjoy a lot of his public work."

"Jim doesn't really like to look at anyone," Anniek Hansen told me. "I say, 'Just look at them!'"

Throughout the 1980s and '90s, the evidence of climate changea"and its potential hazardsa"continued to grow. Hansen kept expecting the political system to respond. This, after all, was what had happened with the ozone problem. Proof that chlorofluorocarbons were destroying the ozone layer came in 1985, when British scientists discovered that an ozone "hole" had opened up over Antarctica. The crisis was resolveda"or, at least, prevented from growing worsea"by an international treaty phasing out chlorofluorocarbons, which was ratified in 1987.

"At first, Jim's work didn't take an activist bent at all," the writer Bill McKibben, who has followed Hansen's career for more than twenty years and who helped organize the anticoal protest in D.C., told me. "I think he thought, as did I, If we get this set of facts out in front of everybody, they're so powerfula"overwhelminga"that people will do what needs to be done. Of course, that was naive on both our parts."

As recently as the George W. Bush administration, Hansen was still operating as if getting the right facts in front of the right people would be enough. In 2001 he was invited to speak to Vice President d.i.c.k Cheney and other high-level administration officials. For the meeting, he prepared a detailed presentation t.i.tled "The Forcings Underlying Climate Change." In 2003 he was invited to Washington again, to meet with the head of the Council on Environmental Quality at the White House. This time he offered a presentation on what ice-core records show about the sensitivity of the climate to changes in greenhouse-gas concentrations. But by 2004 the administration had dropped any pretense that it was interested in the facts about climate change. That year NASA, reportedly at the behest of the White House, insisted that all communications between GISS scientists and the outside world be routed through political appointees at the agency. The following year, the administration prevented GISS from posting its monthly temperature data on its website, ostensibly on the ground that proper protocols had not been followed. (The data showed that 2005 was likely to be the warmest year on record.) Hansen was also told that he couldn't grant a routine interview to National Public Radio. When he spoke out about the restrictions, scientists at other federal agencies complained that they were being similarly treated, and a new term was invented: government scientists, it was said, were being "Hansenized."

"He had been waiting all this time for global warming to become the issue that ozone was," Anniek Hansen told me. "And he's very patient. And he just kept on working and publishing, thinking that someone would do something." She went on, "He started speaking out, not because he thinks he's good at it, not because he enjoys it, but because of necessity."

"When Jim makes up his mind, he pursues whatever conclusion he has to the end point," Michael Oppenheimer said. "And he's made up his mind that you have to pull out all the stops at this point, and that all his scientific efforts would come to naught if he didn't also involve himself in political action." Starting in 2007, Hansen began writing to world leaders, including Prime Minister Gordon Brown, of Britain, and Yasuo f.u.kuda, then the prime minister of j.a.pan. In December 2008, he composed a personal appeal to Barack and Mich.e.l.le Obama.

"A stark scientific conclusion, that we must reduce greenhouse gases below present amounts to preserve nature and humanity, has become clear," Hansen wrote. "It is still feasible to avert climate disasters, but only if policies are consistent with what science indicates to be required." Hansen gave the letter to Obama's chief science adviser, John Holdren, with whom he is friendly, and Holdren, he says, promised to deliver it. But Hansen never heard back, and by the spring he had begun to lose faith in the new administration. (In an e-mail, Holdren said that he could not discuss "what I have or haven't given or said to the President.") "I had had hopes that Obama understood the reality of the issue and would seize the opportunity to marry the energy and climate and national-security issues and make a very strong program," Hansen told me. "Maybe he still will, but I'm getting bad feelings about it."

There are lots of ways to lose an audience with a discussion of global warming, and new ones, it seems, are being discovered all the time. As well as anyone, Hansen ought to know this; still, he persists in trying to make contact. He frequently gives public lectures; just in the past few months, he has spoken to Native Americans in Washington, D.C.; college students at Dartmouth; high school students in Copenhagen; concerned citizens, including King Harald, in Oslo; renewable-energy enthusiasts in Milwaukee; folk music fans in Beacon, New York; and public health professionals in Manhattan.

In April I met up with Hansen at the state capitol in Concord, New Hampshire, where he had been invited to speak by local anticoal activists. There had been only a couple of days to publicize the event; nevertheless, more than 250 people showed up. I asked a woman from the town of Ossipee why she had come. "It's a once-in-a-lifetime opportunity to hear bad news straight from the horse's mouth," she said. For the event, Hansen had, as usual, prepared a PowerPoint presentation. It was projected onto a screen beside a faded portrait of George Washington. The first slide gave the t.i.tle of the talk, "The Climate Threat to the Planet," along with the disclaimer "Any statements relating to policy are personal opinion."

Hansen likes to begin his talk with a highly compressed but still perilously long discussion of climate history, beginning in the early Eocene, some 50 million years ago. At that point, CO2 levels were high and, as Hansen noted, the world was very warm: there was practically no ice on the planet, and palm trees grew in the Arctic. Then CO2 levels began to fall. No one is entirely sure why, but one possible cause has to do with weathering processes that, over many millennia, allow carbon dioxide from the air to get bound up in limestone. As CO2 levels declined, the planet grew cooler; Hansen flashed some slides on the screen, which showed that between 50 million and 35 million years ago, deep ocean temperatures dropped by more than 10 degrees. Eventually, around 34 million years ago, temperatures sank low enough that glaciers began to form on Antarctica. By around 3 million years agoa"perhaps earliera"permanent ice sheets had begun to form in the Northern Hemisphere as well. Then, about 2 million years ago, the world entered a period of recurring glaciations. During the ice agesa"the most recent one ended about 12,000 years agoa"CO 2 levels dropped even further.

What is now happening, Hansen explained to the group in New Hampshire, is that climate history is being run in reverse and at high speed, like a ca.s.sette tape on rewind. Carbon dioxide is being pumped into the air some ten thousand times faster than natural weathering processes can remove it.

"So humans now are in charge of atmospheric composition," Hansen said. Then he corrected himself: "Well, we're determining it, whether we're in charge or not."

Among the many risks of running the system backward is that the ice sheets formed on the way forward will start to disintegrate. Once it begins, this process is likely to be self-reinforcing. "If we burn all the fossil fuels and put all that CO2 into the atmosphere, we will be sending the planet back to the ice-free state," Hansen said. "It will take a while to get therea"ice sheets don't melt instantaneouslya"but that's what we will be doing. And if you melt all the ice, sea levels will go up two hundred and fifty feet. So you can't do that without producing a different planet."

There's no precise term for the level of CO2 that will a.s.sure a climate disaster; the best that scientists and policymakers have been able to come up with is the phrase "dangerous anthropogenic interference," or DAI. Most official discussions have been premised on the notion that DAI will not be reached until CO2 levels. .h.i.t 450 parts per million. Hansen, however, has concluded that the threshold for DAI is much lower.

"The bad news is that it's become clear that the dangerous amount of carbon dioxide is no more than three hundred and fifty parts per million," he told the crowd in Concord. The really bad news is that CO2 levels have already reached 385 parts per million. (For the ten thousand years prior to the industrial revolution, carbon dioxide levels were about 280 parts per million, and if current emissions trends continue they will reach 450 parts by around 2035.) Once you accept that CO2 levels are already too high, it's obvious, Hansen argues, what needs to be done. He displayed a chart of known fossil fuel reserves represented in terms of their carbon content. There was a short bar for oil, a shorter bar for natural gas, and a tall bar for coal.

"We've already used about half of the oil," he observed. "And we're going to use all of the oil and natural gas that's easily available. It's owned by Russia and Saudi Arabia, and we can't tell them not to sell it. So, if you look at the size of these fossil fuel reservoirs, it becomes very clear. The only way we can constrain the amount of carbon dioxide in the atmosphere is to cut off the coal source, by saying either we will leave the coal in the ground or we will burn it only at power plants that actually capture the CO2." Such power plants are often referred to as "clean-coal plants." Although there has been a great deal of talk about them lately, at this point there are no clean-coal plants in commercial operation, and, for a combination of technological and economic reasons, it's not clear that there ever will be.

Hansen continued, "If we had a moratorium on any new coal plants and phased out existing ones over the next twenty years, we could get back to three hundred and fifty parts per million within several decades." Reforestation, for example, if practiced on a ma.s.sive scale, could begin to draw global CO2 levels down, Hansen says, "so it's technically feasible." But "it requires us to take action promptly."

Coincidentally, that afternoon a vote was scheduled in the New Hampshire state legislature on a proposal involving the state's largest coal-fired power plant, the Merrimack Station, in the town of Bow. The station's owner was planning to spend several hundred million dollars to reduce mercury emissions from the planta"a cost that it planned to pa.s.s on to ratepayers. Hansen, who said he thought the plant should simply be shut, called the plan a "terrible waste of money." A lawmaker sympathetic to this view had introduced a bill calling for more study of the project, but, as several people who came up to speak to Hansen after his talk explained, it was opposed by the state's construction unions and seemed headed for defeat. (Less than an hour later, the bill was rejected in committee by a unanimous vote.) "I a.s.sume you're used to telling policymakers the truth and then having them ignore you," one man said to Hansen.

Hansen smiled ruefully. "You're right."

In scientific circles, worries about DAI are widespread. During the past few years, researchers around the world have noticed a disturbing trend: the planet is changing faster than had been antic.i.p.ated. Antarctica, for example, had not been expected to show a net loss of ice for another century, but recent studies indicate that the continent's ma.s.sive ice sheets are already shrinking. At the other end of the globe, the Arctic ice cap has been melting at a shocking rate; the extent of the summer ice is now only a little more than half of what it was just forty years ago. Meanwhile, scientists have found that the arid zones that circle the globe north and south of the tropics have been expanding more rapidly than computer models had predicted. This expansion of the subtropics means that highly populated areas, including the American Southwest and the Mediterranean basin, are likely to suffer more and more frequent droughts.

"Certainly, I think the shrinking of the Arctic ice cap made a very strong impression on a lot of scientists," Spencer Weart, the physicist, told me. "And these things keep popping up. You think, What, another one? Another one? They're almost all in the wrong direction, in the direction of making the change worse and faster."

"In nearly all areas, the developments are occurring more quickly than had been a.s.sumed," Hans Joachim Sch.e.l.lnhuber, the head of Germany's Potsdam Inst.i.tute for Climate Impact Research, recently observed. "We are on our way to a destabilization of the world climate that has advanced much further than most people or their governments realize."

Obama's science adviser, John Holdren, a physicist on leave from Harvard, has said that he believes "any reasonably comprehensive and up-to-date look at the evidence makes clear that civilization has already generated dangerous anthropogenic interference in the climate system."

There is also broad agreement among scientists that coal represents the most serious threat to the climate. Coal now provides half the electricity in the United States. In China, that figure is closer to 80 percent, and a new coal-fired power plant comes online every week or two. As oil supplies dwindle, there will still be plenty of coal, which could bea"and in some places already is beinga"converted into a very dirty liquid fuel. Before Steven Chu, a n.o.bel Prize-winning physicist, was appointed to his current post as energy secretary, he said in a speech, "There's enough carbon in the ground to really cook us. Coal is my worst nightmare." (These are lines that Hansen is fond of invoking.) A couple of months ago, seven prominent climate scientists from Australia wrote an open letter to the owners of that country's major utility companies urging that "no new coal-fired power stations, except ones that have ZERO emissions," be built. They also recommended an "urgent program" to phase out old plants.

"The unfortunate reality is that genuine action on climate change will require that existing coal-fired power stations cease to operate in the near future," the group wrote.

But if Hansen's anxieties about DAI and coal are broadly shared, he is still, among climate scientists, an outlier. "Almost everyone in the scientific community is prepared to say that if we don't do something now to reverse the direction we're going in we either already are or will very, very soon be in the danger zone," Naomi Oreskes, a historian of science and a provost at the University of California at San Diego, told me. "But Hansen talks in stronger terms. He's using adjectives. He has started to speak in moral terms, and that always makes scientists uncomfortable."

Hansen is also increasingly isolated among climate activists. "I view Jim Hansen as heroic as a scientist," Eileen Claussen, the president of the Pew Center on Global Climate Change, said. "He was there at the beginning, he's faced all kinds of pressures politically, and he's done a terrific job, I think, of keeping focused. But I wish he would stick to what he really knows. Because I don't think he has a realistic view of what is politically possible, or what the best policies would be to deal with this problem."

In Washington, the only approach to limiting emissions that is seen as having any chance of being enacted is a so-called cap and trade system. Under such a system, the government would set an overall cap for CO2 emissions, then allocate allowances to major emitters, like power plants and oil refineries, which could be traded on a carbon market. In theory, at least, the system would discourage fossil fuel use by making emitters pay for what they are putting out. But to the extent that such a system has been tried, by the members of the European Union, its results so far are inconclusive, and Hansen argues that it is essentially a sham. (He re cently referred to it as "the Temple of Doom.") What is required, he insists, is a direct tax on carbon emissions. The tax should be significant at the starta"equivalent to roughly a dollar per gallon for gasolinea"and then grow steeper over time. The revenues from the tax, he believes, ought to be distributed back to Americans on a per capita basis, so that households that use less energy would actually make money, even as those that use more would find it increasingly expensive to do so.

"The only defense of this monstrous absurdity that I have heard," Hansen wrote a few weeks ago, referring to a cap and trade system, "is 'Well, you are right, it's no good, but the train has left the station.' If the train has left, it had better be derailed soon or the planet, and all of us, will be in deep doo-doo."

GISS's headquarters, at 112th Street and Broadway, sits above Tom's Restaurant, the diner made famous by Seinfeld and Suzanne Vega. Hansen has occupied the same office, on the seventh floor, since he became the director of the inst.i.tute, almost three decades ago. One day last month, I went to visit him there. Hansen told me that he had been trying to computerize his old files; still, the most striking thing about the s.p.a.cious office, which is largely taken up by three wooden tables, is that every available surface is covered with stacks of paper.

During the week, Hansen lives in an apartment just a few blocks from his office, but on weekends he and Anniek frequently go to an eighteenth-century house that they own in Bucks County, Pennsylvania, and their son and daughter, who have children of their own, come to visit. Hansen dotes on his grandchildrena"in many hours of conversation with me, just about the only time that he spoke with unalloyed enthusiasm was when he discussed planting trees with them this springa"and he claims they are the major reason for his activism. "I decided that I didn't want my grandchildren to say 'Opa understood what was happening, but he didn't make it clear,'" he explained.

The day that I visited Hansen's office, the House Energy and Commerce Committee was beginning its markup of a cap and trade bill cosponsored by the committee's chairman, Henry Waxman, of California. The billa"the American Clean Energy and Security Acta"has the stated goal of cutting the country's carbon emissions by 17 percent by 2020. It is the most significant piece of climate legislation to make it this far in the House. Hansen pointed out that the bill explicitly allows for the construction of new coal plants and predicted that it would, if pa.s.sed, prove close to meaningless. He said that he thought it would probably be best if the bill failed so that Congress could "come back and do it more sensibly."

I said that if the bill failed I thought it was more likely that Congress would let the issue drop, and that was one reason most of the country's major environmental groups were backing it.

"This is just stupidity on the part of environmental organizations in Washington," Hansen said. "The fact that some of these organizations have become part of the Washington 'go along, get along' establishment is very unfortunate."

Hansen argues that politicians willfully misunderstand climate science; it could be argued that Hansen just as willfully misunderstands politics. In order to stabilize carbon dioxide levels in the atmosphere, annual global emissions would have to be cut by something on the order of three-quarters. In order to draw them down, agricultural and forestry practices would have to change dramatically as well. So far, at least, there is no evidence that any nation is willing to take anything approaching the necessary steps. On the contrary, almost all the trend lines point in the opposite direction. Just because the world desperately needs a solution that satisfies both the scientific and the political constraints doesn't mean one necessarily exists.

For his part, Hansen argues that while the laws of geophysics are immutable, those of society are ours to determine. When I said that it didn't seem feasible to expect the United States to give up its coal plants, he responded, "We can point to other countries being fifty percent more energy-efficient than we are. We're getting fifty percent of our electricity from coal. That alone should provide a pretty strong argument."

Then what about China and India?

Both countries are likely to suffer very severely from dramatic climate change, he said. "They're going to recognize that. In fact, they already are beginning to recognize that.

"It's not unrealistic," he went on. "But the policies have to push us in that direction. And, as long as we let the politicians and the people who are supporting them continue to set the rules, such that 'business as usual' continues, or small tweaks to 'business as usual,' then it is unrealistic. So we have to change the rules." He said that he was thinking of attending another demonstration soon, in West Virginia coal country.

ELIZABETH KOLBERT The Sixth Extinction?.

FROM The New Yorker.

THE TOWN OF El Valle de Antn, in central Panama, sits in the middle of a volcanic crater formed about a million years ago. The crater is almost four miles across, but when the weather is clear you can see the jagged hills that surround the town, like the walls of a ruined tower. El Valle has one main street, a police station, and an open-air market that offers, in addition to the usual hats and embroidery, what must be the world's largest selection of golden-frog figurines. There are golden frogs sitting on leaves anda"more difficult to understanda"golden frogs holding cell phones. There are golden frogs wearing frilly skirts, and golden frogs striking dance poses, and ashtrays featuring golden frogs smoking cigarettes through a holder, after the fashion of FDR. The golden frog, which is bright yellow with dark brown splotches, is endemic to the area around El Valle. It is considered a lucky symbol in Panamaa"its image is often printed on lottery ticketsa"though it could just as easily serve as an emblem of disaster.

In the early 1990s, an American graduate student named Karen Lips established a research site about two hundred miles west of El Valle, in the Talamanca Mountains, just over the border in Costa Rica. Lips was planning to study the local frogs, some of which, she later discovered, had never been identified. In order to get to the site, she had to drive two hours from the nearest towna"the last part of the trip required tire chainsa"and then hike for an hour through the rainforest.

Lips spent two years living in the mountains. "It was a wonderland," she recalled recently. Once she had collected enough data, she left to work on her dissertation. She returned a few months later, and, though nothing seemed to have changed, she could hardly find any frogs. Lips couldn't figure out what was happening. She collected all the dead frogs that she came acrossa"there were only a half dozen or soa"and sent their bodies to a veterinary pathologist in the United States. The pathologist was also baffled: the specimens, she told Lips, showed no signs of any known disease.

A few years went by. Lips finished her dissertation and got a teaching job. Since the frogs at her old site had pretty much disappeared, she decided that she needed to find a new location to do research. She picked another isolated spot in the rainforest, this time in western Panama. Initially, the frogs there seemed healthy. But before long, Lips began to find corpses lying in the streams and moribund animals sitting on the banks. Sometimes she would pick up a frog and it would die in her hands. She sent some specimens to a second pathologist in the United States, and, once again, the pathologist had no idea what was wrong.

Whatever was killing Lips's frogs continued to move, like a wave, east across Panama. By 2002 most frogs in the streams around Santa F, a town in the province of Veraguas, had been wiped out. By 2004 the frogs in the national park of El Cop, in the province of Cocl, had all but disappeared. At that point, golden frogs were still relatively common around El Valle; a creek not far from the town was nicknamed Thousand Frog Stream. Then, in 2006, the wave hit.

Of the many species that have existed on Eartha"estimates run as high as 50 billiona"more than 99 percent have disappeared. In light of this, it is sometimes joked that all of life today amounts to little more than a rounding error.

Records of the missing can be found everywhere in the world, often in forms that are difficult to overlook. And yet extinction has been a much contested concept. Throughout the eighteenth century, even as extraordinary fossils were being unearthed and put on exhibit, the prevailing view was that species were fixed, created by G.o.d for all eternity. If the bones of a strange creature were found, it must mean that that creature was out there somewhere.

"Such is the economy of nature," Thomas Jefferson wrote, "that no instance can be produced, of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken." When, as president, he dispatched Meriwether Lewis and William Clark to the Northwest, Jefferson hoped that they would come upon live mastodons roaming the region.

The French naturalist Georges Cuvier was more skeptical. In 1812 he published an essay on the "Revolutions on the Surface of the Globe," in which he asked, "How can we believe that the immense mastodons, the gigantic megatheriums, whose bones have been found in the earth in the two Americas, still live on this continent?" Cuvier had conducted studies of the fossils found in gypsum mines in Paris and was convinced that many organisms once common to the area no longer existed. These he referred to as espces perdues, or lost species. Cuvier had no way of knowing how much time had elapsed in forming the fossil record. But, as the record indicated that Paris had, at various points, been under water, he concluded that the espces perdues had been swept away by sudden cataclysms.

"Life on this earth has often been disturbed by dreadful events," he wrote. "Innumerable living creatures have been victims of these catastrophes." Cuvier's essay was translated into English in 1813 and published with an introduction by the Scottish naturalist Robert Jameson, who interpreted it as proof of Noah's flood. It went through five editions in English and six in French before Cuvier's death in 1832.

Charles Darwin was well acquainted with Cuvier's ideas and the theological spin they had been given. (He had studied natural history with Jameson at the University of Edinburgh.) In his theory of natural selection, Darwin embraced extinction; it was, he realized, essential that some species should die out as new ones were created. But he believed that this happened only slowly. Indeed, he claimed that it took place more gradually even than speciation: "The complete extinction of the species of a group is generally a slower process than their production." In On the Origin of Species, published in the fall of 1859, Darwin heaped scorn on the catastrophist approach: "So profound is our ignorance, and so high our presumption, that we marvel when we hear of the extinction of an organic being; and as we do not see the cause, we invoke cataclysms to desolate the world."

By the start of the twentieth century, this view had become dominant, and to be a scientist meant seeing extinction as Darwin did. But Darwin, it turns out, was wrong.

Over the past half-billion years, there have been at least twenty ma.s.s extinctions, when the diversity of life on Earth has suddenly and dramatically contracted. Five of thesea"the so-called Big Fivea"were so devastating that they are usually put in their own category. The first took place during the late Ordovician period, nearly 450 million years ago, when life was still confined mainly to water. Geological records indicate that more than 80 percent of marine species died out. The fifth occurred at the end of the Cretaceous period, 65 million years ago. The end-Cretaceous event exterminated not just the dinosaurs but 75 percent of all species on Earth.

The significance of ma.s.s extinctions goes beyond the sheer number of organisms involved. In contrast to ordinary, or so-called background, extinctions, which claim species that, for one reason or another, have become unfit, ma.s.s extinctions strike down the fit and the unfit at once. For example, brachiopods, which look like clams but have an entirely different anatomy, dominated the ocean floor for hundreds of millions of years. In the third of the Big Five extinctionsa"the end-Permiana"the hugely successful brachiopods were nearly wiped out, along with trilobites, blastoids, and eurypterids. (In the end-Permian event, more than 90 percent of marine species and 70 percent of terrestrial species vanished; the event is sometimes referred to as "the mother of ma.s.s extinctions" or "the great dying.") Once a ma.s.s extinction occurs, it takes millions of years for life to recover, and when it does it generally has a new cast of characters; following the end-Cretaceous event, mammals rose up (or crept out) to replace the departed dinosaurs. In this way, ma.s.s extinctions, though missing from the original theory of evolution, have played a determining role in evolution's course; as Richard Leakey has put it, such events "restructure the biosphere" and so "create the pattern of life." It is now generally agreed among biologists that another ma.s.s extinction is underway. Though it's difficult to put a precise figure on the losses, it is estimated that if current trends continue, by the end of this century as many as half of Earth's species will be gone.