Environment / Earth Science

By 2100 Siberia as we know it may not exist—all that frozen ground may have thawed. The defrosting could release nearly 1,000 gigatons of carbon stored in the permafrost and hasten global warming, according to a report in June. The unnerving new estimate puts permafrost up there with soils (1,500 gigatons) and vegetation (650 gigatons), Earth's second and third largest repositories of carbon after the oceans. In a separate study, Katey Walter, an aquatic ecologist at the University of Alaska at Fairbanks, showed that much of this buried carbon may emerge as methane, a greenhouse gas some 20 times more powerful than carbon dioxide. One type of permafrost called yedoma is full of grass roots, bones, and other biological material. For tens of thousands of years, this organic matter has been in cold storage; when permafrost melts, it gives rise to thaw lakes, where the organics decompose and release bubbles of methane. While monitoring two Arctic thaw lakes for 13 months, Walter's team found that they gave off five times as much methane as previously estimated. She also showed that the lakes are growing, potentially starting a feedback loop that could lead to more rapid warming.

Samir S. Patel

In 2005 MIT climatologist Kerry Emanuel stirred intense debate with a study indicating that global warming had caused hurricanes to nearly double in strength since the 1970s. In 2006 other researchers rushed in to test the claim. Their studies strengthen the theory that a warmer climate heats the ocean surface and fuels massive storms. But the core question—is global warming leading to more extreme weather?—remains frustratingly unresolved.

Although hurricane records date back more than a century, they have been gathered using techniques of varying accuracy, such that it is often hard to compare new data with old. This motley record has divided researchers. Meteorologists, attuned to ever-shifting daily weather, are less familiar and less comfortable with the long-term data set. Climatologists, who study longer timescales and are used to working with incomplete records, have more faith in the data, yet know less about the day-to-day dynamics of hurricanes.

"Tropical meteorologists, we're a skeptical bunch," says John Knaff of Colorado State University. Kevin Trenberth, a climatologist at the National Center for Atmospheric Research, counters that the hurricane records, although messy and full of confounding factors, can reveal long-term trends, particularly in the Atlantic.

So far, the results from climate models do not match the dramatic rise in storm intensity seen by Emanuel. But researchers on both sides agree that current models are still inadequate. Georgia Tech climatologist Peter Webster and others are looking at better ways to mine the hurricane record by excluding the most heavily disputed data.

Webster is now studying the duration of the hurricane season each year, from the first tropical cyclone to the last. His findings, which are not yet published, are not reassuring. "The length of the hurricane season has been expanding," he says, "increasing by about five days per decade—about 15 days since 1970."

Elise Kleeman

Katrina. Rita. Wilma. Are humans to blame?

Discover talks hurricanes with meteorologist William Gray, one of the world's most famous hurricane experts.

Geologists at Stanford settled a long-simmering dispute over the age of the Sierra Nevada range by studying gravel that was soaked with rainwater eons ago. The residue of trapped water contains both regular hydrogen atoms and a heavier isotope, deuterium. Deuterium-laden water falls at lower altitudes, so the ratio of isotopes can indicate how high the gravel was when the rain fell. The ratios in Sierra samples 45 million years old resemble those in modern rainfall from the same locations, which suggests the range's height hasn't changed for tens of millions of years. Most scientists had put the Sierras' age at under 5 million years old.

Kathy A. Svitil