JUSTIN GILLIS
LAMONT, Okla. — For decades, a small group of scientific dissenters has been trying to shoot holes in the prevailing science of climate change, offering one reason after another why the outlook simply must be wrong.
Over time, nearly every one of their arguments has been knocked down by accumulating evidence, and polls say 97 percent of working climate scientists now see global warming as a serious risk.
Yet in recent years, the climate change skeptics have seized on one last argument that cannot be so readily dismissed. Their theory is that clouds will save us.
They acknowledge that the human release of greenhouse gases will cause the planet to warm. But they assert that clouds — which can either warm or cool the earth, depending on the type and location — will shift in such a way as to counter much of the expected temperature rise and preserve the equable climate on which civilization depends.
Their theory exploits the greatest remaining mystery in climate science, the difficulty that researchers have had in predicting how clouds will change. The scientific majority believes that clouds will most likely have a neutral effect or will even amplify the warming, perhaps strongly, but the lack of unambiguous proof has left room for dissent.
“Clouds really are the biggest uncertainty,” said Andrew E. Dessler, a climate researcher at Texas A&M. “If you listen to the credible climate skeptics, they’ve really pushed all their chips onto clouds.”
Richard S. Lindzen, a professor of meteorology at the Massachusetts Institute of Technology, is the leading proponent of the view that clouds will save the day. His stature in the field — he has been making seminal contributions to climate science since the 1960s — has amplified his influence.
Dr. Lindzen says the earth is not especially sensitive to greenhouse gases because clouds will react to counter them, and he believes he has identified a specific mechanism. On a warming planet, he says, less coverage by high clouds in the tropics will allow more heat to escape to space, countering the temperature increase.
His idea has drawn withering criticism from other scientists, who cite errors in his papers and say proof is lacking. Enough evidence is already in hand, they say, to rule out the powerful cooling effect from clouds that would be needed to offset the increase of greenhouse gases.
However, politicians looking for reasons not to tackle climate change have embraced Dr. Lindzen and other skeptics, elevating their role in the public debate.
Dr. Lindzen has obliged by assuring them that they are running no risks by refusing to enact emission limits. “There’s been a lot of scare stuff put out that just doesn’t make sense,” he said in an interview.
Some politicians have welcomed that message, regularly calling Dr. Lindzen and a handful of other contrarian scientists before Congressional committees. During a hearing before a House subcommittee, Representative Dana Rohrabacher, a California Republican and vocal global warming skeptic, complained that “in the scientific community, there are people trying to tell us that we have got to accept draconian changes in our way of life mandated by law because the CO2 that we are emitting is going to cause drastic consequences to the planet’s climate.”
He repeatedly sought affirmation from Dr. Lindzen for his views, and got it.
At gatherings of climate change skeptics on both sides of the Atlantic, Dr. Lindzen has been treated as a star. During a debate in Australia over carbon taxes, his work was cited repeatedly. When he appears at conferences of the Heartland Institute, the primary American organization pushing climate change skepticism, he is greeted by thunderous applause.
While the scientific majority acknowledges that the lingering uncertainty about clouds plays into the hands of skeptics like Dr. Lindzen, they say that he has gone beyond any reasonable reading of the evidence to provide a dangerous alibi for inaction.
Dr. Lindzen is “feeding upon an audience that wants to hear a certain message, and wants to hear it put forth by people with enough scientific reputation that it can be sustained for a while, even if it’s wrong science,” said Christopher S. Bretherton, an atmospheric researcher at the University of Washington. “I don’t think it’s intellectually honest at all.”
With climate policy nearly paralyzed in the United States, many other governments have also declined to take action, and worldwide emissions of greenhouse gases are soaring.
Natural Thermostats
Clouds are so familiar they are easy to take for granted, but scientists point out that they have an enormous effect on the climate.
The energy that drives life on earth arrives as sunlight. To remain at a steady temperature, the earth has to return the energy it receives back to space, primarily as heat. Clouds alter the energy flow in both directions.
On balance, in today’s climate, clouds cool the earth. Dense, low-lying clouds are responsible for most of that effect, because they reflect considerable sunlight back to space. Many high, thin clouds have the opposite influence, allowing incoming sunshine to pass through but effectively trapping heat that is trying to escape.
“It’s like putting a lid on a pot on the stove,” said Andreas Muhlbauer, a cloud researcher at the University of Washington.
Humans are perturbing the earth’s heat balance by releasing greenhouse gases. Chemists proved in the 19th century that these gases, especially the carbon dioxide that results from burning fossil fuels, work like an invisible blanket in the atmosphere, blocking some heat that is attempting to escape to space. In the mid-20th century, as it became clear how fast carbon dioxide levels were rising, some scientists began to predict a warming of the planet. But they also realized that an exact forecast was difficult for several reasons, especially the question of how clouds would react.
Researchers are virtually certain the amount of water vapor in the atmosphere will rise with temperature, and evidence suggests this is already happening. But that does not say much about the type or location of clouds that will condense from the vapor.
Scientists use sophisticated computer programs to forecast future climate, but the computers are not yet powerful enough to predict the behavior of individual clouds across the whole earth over a century, which forces the researchers to use rough approximations.
The most elaborate computer programs have agreed on a broad conclusion: clouds are not likely to change enough to offset the bulk of the human-caused warming. Some of the analyses predict that clouds could actually amplify the warming trend sharply through several mechanisms, including a reduction of some of the low clouds that reflect a lot of sunlight back to space. Other computer analyses foresee a largely neutral effect. The result is a big spread in forecasts of future temperature, one that scientists have not been able to narrow much in 30 years of effort.
The earth’s surface has already warmed about 1.4 degrees Fahrenheit since the Industrial Revolution, most of that in the last 40 years. Modest as it sounds, it is an average for the whole planet, representing an enormous addition of heat. An even larger amount is being absorbed by the oceans. The increase has caused some of the world’s land ice to melt and the oceans to rise.
By midcentury, the level of greenhouse gases in the atmosphere is expected to double compared with the value that prevailed before the Industrial Revolution. At the low end, computers predict that the earth could warm in response by another 2 degrees Fahrenheit. The likelier figure, the analyses say, is 4 degrees. At the high end of projections, the warming could exceed 8 degrees. In all possible outcomes, the warming over land would be roughly twice the global average, and the warming in the Arctic greater still.
Even in the low projection, many scientists say, the damage could be substantial. In the high projection, some polar regions could heat up by 20 or 25 degrees Fahrenheit — more than enough, over centuries or longer, to melt the Greenland ice sheet, raising sea level by a catastrophic 20 feet or more. Vast changes in rainfall, heat waves and other weather patterns would most likely accompany such a large warming.
“The big damages come if the climate sensitivity to greenhouse gases turns out to be high,” said Raymond T. Pierrehumbert, a climate scientist at the University of Chicago. “Then it’s not a bullet headed at us, but a thermonuclear warhead.”
A major goal of climate research is to improve the way clouds are represented in the computer analyses, which should narrow the range of predicted temperatures. And some of the most important data that researchers need to do so are streaming from a hilltop in rural Oklahoma, near the town of Lamont, where the Department of Energy runs the world’s largest facility for measuring the behavior of clouds.
Accuracy is an overriding goal there. One recent morning, Patrick Dowell, a technician, worked his way across the hill with a rag in hand, carefully dusting dozens of instruments pointed at the sky. When his fingers knocked one gauge off kilter, tiny motors whirred and the device snapped back to position, as though annoyed with him.
“When you clean it,” Mr. Dowell said, “it kind of fights you.”
The questions that scientists still need to answer are voluminous. For instance, they want a better idea of how clouds form at a microscopic scale, how their behavior varies under different atmospheric conditions, and how sensitive they are to higher temperatures.
Recently, $30 million worth of new radars have been installed in Oklahoma and at other research facilities, promising a better view of the innards of clouds. Satellites are also supplying better data, and theories of the atmosphere are improving. “I feel like we’re on our way to doing a lot better,” said Anthony D. Del Genio, a researcher with NASA.
But the problem of how clouds will behave in a future climate is not yet solved — making the unheralded field of cloud research one of the most important pursuits of modern science.
A Feedback Loop?
Among the many climate skeptics who plaster the Internet with their writings, hardly any have serious credentials in the physics of the atmosphere. But a handful of contrarian scientists do. The most influential is Dr. Lindzen.
Dr. Lindzen accepts the elementary tenets of climate science. He agrees that carbon dioxide is a greenhouse gas, calling people who dispute that point “nutty.” He agrees that the level of it is rising because of human activity and that this should warm the climate.
But for more than a decade, Dr. Lindzen has said that when surface temperature increases, the columns of moist air rising in the tropics will rain out more of their moisture, leaving less available to be thrown off as ice, which forms the thin, high clouds known as cirrus. Just like greenhouse gases, these cirrus clouds act to reduce the cooling of the earth, and a decrease of them would counteract the increase of greenhouse gases.
Dr. Lindzen calls his mechanism the iris effect, after the iris of the eye, which opens at night to let in more light. In this case, the earth’s “iris” of high clouds would be opening to let more heat escape.
When Dr. Lindzen first published this theory, in 2001, he said it was supported by satellite records over the Pacific Ocean. But other researchers quickly published work saying that the methods he had used to analyze the data were flawed and that his theory made assumptions that were inconsistent with known facts. Using what they considered more realistic assumptions, they said they could not verify his claims.
Today, most mainstream researchers consider Dr. Lindzen’s theory discredited. He does not agree, but he has had difficulty establishing his case in the scientific literature. Dr. Lindzen published a paper in 2009 offering more support for his case that the earth’s sensitivity to greenhouse gases is low, but once again scientists identified errors, including a failure to account for known inaccuracies in satellite measurements.
Dr. Lindzen acknowledged that the 2009 paper contained “some stupid mistakes” in his handling of the satellite data. “It was just embarrassing,” he said in an interview. “The technical details of satellite measurements are really sort of grotesque.”
Last year, he tried offering more evidence for his case, but after reviewers for a prestigious American journal criticized the paper, Dr. Lindzen published it in a little-known Korean journal.
Dr. Lindzen blames groupthink among climate scientists for his publication difficulties, saying the majority is determined to suppress any dissenting views. They, in turn, contend that he routinely misrepresents the work of other researchers.
“If I’m right, we’ll have saved money” by avoiding measures to limit emissions, Dr. Lindzen said in the interview. “If I’m wrong, we’ll know it in 50 years and can do something.”
But mainstream scientists counter that society’s impulse to wait only heightens the risks.
Ultimately, as the climate continues warming and more data accumulate, it will become obvious how clouds are reacting. But that could take decades, scientists say, and if the answer turns out to be that catastrophe looms, it would most likely be too late. By then, they say, the atmosphere would contain so much carbon dioxide as to make a substantial warming inevitable, and the gas would not return to a normal level for thousands of years.
Researchers are trying various shortcuts to get a rapid answer. One of those is to use short-term natural variations, such as the El Niño cycle, to see how clouds react to higher ocean temperatures. Dr. Dessler, the Texas A&M researcher, did that recently. His analysis, while not definitive, offered some evidence that clouds will exacerbate the long-term planetary warming, just as many of the computer programs have predicted. Most, but not all, papers relying on the historical cloud record have come to similar conclusions.
In his Congressional appearances, speeches and popular writings, Dr. Lindzen offers little hint of how thin the published science supporting his position is. Instead, starting from his disputed iris mechanism, he makes what many of his colleagues see as an unwarranted leap of logic, professing near-certainty that climate change is not a problem society needs to worry about.
“You have politicians who are being told if they question this, they are anti-science,” Dr. Lindzen said. “We are trying to tell them, no, questioning is never anti-science.”
Among the experts most offended by Dr. Lindzen’s stance are many of his colleagues in the M.I.T. atmospheric sciences department, some of whom were once as skeptical as he about climate change.
“Even if there were no political implications, it just seems deeply unprofessional and irresponsible to look at this and say, ‘We’re sure it’s not a problem,’ ” said Kerry A. Emanuel, another M.I.T. scientist. “It’s a special kind of risk, because it’s a risk to the collective civilization.”
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