Those standing on the two main sides of the climate debate are easy for most Americans to recognize.
There is the majority of researchers who actually study the climate and see abundant evidence that the earth is warming, driven largely by the human burning of fossil fuels. And there is a vocal minority of doubters, many of whom draw on critiques of the science promoted by industry-financed campaigns.
Eighty-three percent of Americans believe the world’s temperature is rising. Now researchers are studying why no one wants to talk about it.
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Coral fossils are hard to find but their fast growth allows researchers to identify how temperatures changed from month to month, rather than annually.
Argo, a system of 3,500 electronic buoys around the world, is collecting data on how oceans trap, redistribute, and release heat. “We’re goingto learn a lot, once we sort of pin down how much heat is going into the oceans,” says one researcher.
And yet the truth, often obscured by the fog of politics, is that the scientists are genuinely uncertain about how fast the warming is happening, what and how strong the negative effects will be, and how quickly those problems will begin showing up in your neighborhood.
That uncertainty has helped make them vulnerable to critics who have a long list of reasons for doubting virtually any science-based warnings, including the consensus hammered out by the United Nations Intergovernmental Panel on Climate Change that carbon-dioxide emissions must be reduced. Some contend the planet has been cooling since a period of unusual warmth in 1998. Some suggest wide temperature variations are natural. Some argue that the earth has processes that counteract any excess heat.
Scientists can explain why they’re not persuaded by those and many other objections. But—153 years after the British physicist John Tyndall proved that the earth’s atmosphere has a greenhouse effect by showing that water vapor absorbs infrared radiation —"there’s just a lot we don’t understand” about how the climate is responding to the increase in temperatures being thrust upon it, says Kim M. Cobb, an associate professor of earth and atmospheric sciences at Georgia Institute of Technology.
Getting better answers is tough work. It involves hunting for coral beneath the Pacific Ocean. It requires climbing through caves for stalagmites. And it means surviving treacherous conditions in the Antarctic. It’s also extremely complicated work, involving calculations so excruciatingly complex that even the world’s most powerful supercomputers can’t yet crunch all the numbers.
The Quest for Data
The basic problem is that climate change, as a natural phenomenon, usually occurs on the scale of centuries. Yet humans have been keeping direct temperature records around the globe, on a reliable and comparable basis, for only about 150 years.
Scientists, therefore, need indirect ways of reconstructing temperatures going back many thousands of years. They are now making major improvements in those methods, with a variety of techniques, often involving studies of natural processes affecting trees, ice, caves, and fossils.
The key to most methods is oxygen, which is found in ice, cave drippings, plants, and calcium-carbonate coral skeletons. Atoms have variations known as isotopes, and the temperature at the time of a specimen’s formation affects the percentage of rare isotopes of oxygen found in those specimens. “So, we can reconstruct the temperature,” Ms. Cobb says.
Coral fossils are proving especially valuable for this task. Their fast growth allows researchers to identify temperatures at a monthly resolution, rather than the annual resolution common with trees, ice cores, and stalagmites. Coral is also important because water covers most of the earth and holds temperatures more evenly and over longer periods of time than do air or land surfaces.
But variations in oxygen isotopes are also affected by salinity levels, raising an additional complication in calculations. And coral fossils are hard to find. Ms. Cobb tracks them down in the tropical Pacific and spends part of her time monitoring the schedules of cruise ships for opportunities to reach the area. Because coral relies on sunlight, it grows only about 20 feet to 40 feet underwater. And it also doesn’t thrive in surf zones, meaning it’s usually found only near the tops of underwater volcanoes. Corals “are delicate, and in a relatively narrow range,” she says.
Future Scenarios
Finding the earth’s past temperatures is only part of the challenge for climate scientists. The other major set of tasks involves learning more about how the earth responds to increased heat. Scientists expect hotter temperatures will melt polar ice caps and flood low-lying cities and countries. Other places could turn to deserts. Many regions of the world may face greater risks of hurricanes and other violent weather. But when? Exactly where? How badly?
Here, too, the tropical Pacific is a focal point because of its role in originating the El Niño and La Niña weather patterns felt worldwide on multiyear cycles. Contrary to skeptics’ claims that temperatures have cooled since 1998 (an assertion now widely disputed), year-to-year variations that do occur merely demonstrate the short-term effects of El Niño, says John W. Nielsen-Gammon, a professor of atmospheric sciences at Texas A&M University. Last year’s record-setting drought in Texas, for instance, was probably driven largely by El Niño, he says, though climate change made it worse.
Meanwhile, the underlying warming trend is persisting, and scientists expect temperatures to make up for lost ground each time El Niño cycles reverse.
One recent study with potential to help scientists understand the effects of El Niño examined dirt dug up from the bottom of Lake Chala, on the Kenya-Tanzania border. The climate there, at the foothills of Kilimanjaro, is heavily driven by El Niño. Strong winds across the lake stir up plant life, which dies each year, leaving clear layers of sediment. The separation of layers in one sediment core was clear enough to give the scientists 25,000 years of temperature data with almost annual resolution.
As they try to make predictions about future effects of climate change, researchers are focused on four broad areas that require better understanding: the circulation patterns of oceans, the mechanics of cloud formation, the effects of airborne particles, and the physics of ice melting.
Each of those systems, as well as the interplay among them, has effects on the temperature of the planet.
Oceans, because they cover so much of the earth, may be the most important system for scientists to understand better if they want to improve their predictions about the future course of climate change. They trap, redistribute, and release huge amounts of heat—but scientists aren’t sure about how much. Their vast size and depth make them extremely difficult to fully understand. The Scripps Institution of Oceanography at the University of California at San Diego is heading one major effort to remedy that. Known as Argo, it is a worldwide system of some 3,500 electronic buoys that automatically submerge and resurface, constantly transmitting data on underwater temperatures into a computerized collection network.
Argo promises “one of the most important new data sets we’re going to get in the near future,” says Chris E. Forest, an associate professor of climate dynamics at Pennsylvania State University’s main campus. “We’re going to learn a lot, once we sort of pin down how much heat is going into the oceans.”
There is evidence that the circulation of water between surface regions and lower depths could minimize, then compound, the effects of atmospheric warming by throwing out more carbon molecules as water temperatures increase. “The ocean in and of itself acts as the flywheel of the climate system,” with the potential to both slow down and then speed up warming trends, Mr. Forest says.
With clouds, it’s not even clear if warming temperatures produce more clouds or fewer. Their effect on the climate is also in question: More dense clouds at a low altitude could mean an overall slowing of the warming process because they reflect more sunlight back to space. An increase in higher, thinner clouds could accelerate the warming by trapping more radiation.
Particles in the air, from pollution or natural causes such as volcanoes, are known to have strong cooling effects. In fact some pollution controls have been associated with atmospheric heating. Airborne particles also play a central role in cloud formation, again with uncertain overall effects.
And scientists are being constantly surprised by the speeds at which sea ice melts. A prime example was the sudden collapse in 2002 of the Larsen B ice shelf, which covered 1,250 square miles of Antarctica at a thickness of 650 feet. Attention is now focused on Antarctica’s 1,600-foot-thick Pine Island Glacier, from which a 350-square-mile chunk appears to be rapidly breaking off.
Crunching the Numbers
As scientists gather better information about temperatures and earth systems, they have the monumental task of pulling it all together. To crunch all of the statistics—hundreds of thousands of years of temperature and atmospheric records, and global circulation patterns of clouds and water—supercomputers are necessary. The hope is that computers will find patterns that can predict what will happen in the future.
Researchers have some of their own predictions, and U.S. universities are working with three main climate-system models to test them. The models have been developed by the NASA Goddard Institute for Space Studies at Columbia University, the Geophysical Fluid Dynamics Lab at Princeton University, and the National Center for Atmospheric Research, which has more than 60 member universities.
Yet as much as researchers still need to learn about oceans and temperatures, their ability to collect data from ice cores and coral fossils already outpaces their ability to run that data through the models. Too few supercomputers exist, and too many other scientific fields demand them.
The nation’s most ambitious supercomputing effort for climate science is based at the Lawrence Livermore National Laboratory, where data are being collected for the next United Nations assessment of global warming. Scientists aiding the U.N. project get the benefit of some of the most advanced supercomputer processing of their models. In other cases, researchers have resorted to cobbling together collections of volunteers with personal computers to try to find enough computing power to test their ideas.
The IPCC’s next assessment report, due in 2014, will be a test of computing power—likely to generate nearly six times the amount of data generated for its most recent report, in 2007.
That report predicted a global temperature rise of 2 to 12 degrees Fahrenheit and a sea-level rise of 7.1 to 23 inches by the end of the current century. Without better calculations and better data sources, those figures are only approximations.
Still, a large majority of scientists believe those estimates are certain enough to require a move away from fossil fuels. “While there are uncertainties,” says Andrew E. Dessler, a professor of atmospheric sciences at Texas A&M University, “the biggest legitimate uncertainties are whether a business-as-usual future gives us two-degree-Celsius warming or four-degree-Celsius warming. The uncertainties are not big enough to include the possibility of near-zero warming in the future.”
Penn State’s Mr. Forest echoes that. “It’s very, very difficult to find a scenario” where the climate would not change drastically in response to the greenhouse gases, he says.
In fact, climate scientists can list several facts on which they’re clear: Increased concentrations of atmospheric carbon produce warming; the polar latitudes and equatorial regions are warming faster than middle latitudes where most people live; and heat waves are intensifying.
Regional variations will be significant, and identifying them is another fundamental challenge for climate research. “This is perhaps one of the biggest thrusts right now in the climate community,” says Axel Timmermann, a professor of oceanography at the University of Hawaii. How is warming happening “on my particular island or in my particular state or in my city?”
Better predictions about regional effects might also prove the key to finally persuading the public to bear the short-term costs necessary to confront climate change.
“If we could ever predict regional droughts, heat waves, or extreme precipitation events with accuracy,” Mr. Dessler says, “and tie that to climate change, then we would see acceptance of the general concept of climate change very rapidly.”
