Siberian Thaw Releases Methane And Accelerates Global Warming
The Siberian permafrost is melting, but that has been happening since the end of the last ice age about 10,000 years ago. What's new, researchers reported in August, is that the thaw appears to be speeding up. As it does, it could release tons of additional methane gas, which has 20 times the greenhouse effect of carbon dioxide, possibly increasing the rate of global warming.
Sergei Kirpotin, a botanist at Tomsk State University in Russia, and Oxford University researcher Judith Marquand say that rising temperatures are increasing the size of lakes in the frozen peat bog of western Siberia. "The most enormous change was between 2003 and 2005—the lakes had really expanded," says Marquand. In some places, "the vegetation can no longer recover from the amount of flooding each year," she says. Because water is darker than permafrost and absorbs more heat, melting can cause even more melting. As the permafrost disappears, carbon-rich material like grass roots, once trapped in icy soil, sinks to lake bottoms, where bacteria convert it into the greenhouse gas methane.
One type of especially carbon-rich permafrost, called Yedoma, holds "500 gigatons of carbon—two and a half times the amount of carbon that's in all the world's tropical forests," says aquatic ecologist Katey Walter of the University of Alaska in Fairbanks. In May Walter and her colleagues reported hot spots in Siberian lakes where methane bubbles up so quickly that ice never forms. "The lake looks like it's boiling," she says, "but it's not boiling with temperature; it's boiling with methane." —Elise Kleeman
Ozone Layer Halts Decline
Efforts during the last quarter century to save the ozone layer are finally paying off. In August a study conducted by the Cooperative Institute for Research in Environmental Sciences in Colorado revealed that ozone measurements have stopped declining over the midlatitudes of the Northern and Southern hemispheres, where the bulk of the world's population resides. Betsy Weatherhead, a coauthor of the study, attributes the apparent improvement to international measures taken to reduce chlorofluorocarbons and other ozone-strafing chemicals.
Although the new findings are encouraging, experts disagree about when ozone density might return to normal, pre-1980 levels over most of the globe. Some scientists believe we may never fully replenish what's been lost. And ozone loss above the Antarctic, where numbing cold creates high-altitude clouds that speed ozone depletion, remains an intractable challenge. "On the one hand, we think we have good news for where people live and get ultraviolet radiation and where we grow our crops," says Weatherhead. "On the other hand, the Antarctic ozone hole could persist for quite a few decades." —Jack Kelley
Tree Rings Tell Hurricane Tales
Are hurricanes increasing in number? Although 2005 broke a record for the number of hurricanes, scientists do not know if it portends a pattern connected to global warming. But at least they have a new tool—tree-growth rings—to help them determine just how bad a bad year is.
Tree rings can tell tales because hurricanes produce rain with low amounts of a specific isotope—oxygen-18. When the rainwater is absorbed by the shallow roots of pine trees, the low oxygen-18 signal is locked in the cellulose that forms rings.
To test the data, University of Tennessee geochemist Claudia Mora and dendrochronologist Henri Grissino-Mayer studied rings from longleaf and slash pines in Valdosta, Georgia. Whenever they found large dips in the oxygen-18 isotope, they found a corresponding historical record of a hurricane. The two now have continuous tree-ring hurricane records for parts of the southeast dating back 227 years, from 1770 to 1997. Their goal: "a 500-year archive with exact dates on everything."
That record could help climatologists understand decade- and century-long variations in hurricane patterns and begin to unravel the impact of global warming on storm cycles. Nonetheless, Mora says tree rings can't show the intensity of a hurricane: "That's the one thing we can't do; hurricanes are dynamic systems. They strengthen, they weaken, and they're moving. We're capturing a record in a stationary tree." —Anne Sasso
Did Mild Weather Kill Pacific Seabirds?
Beginning last spring, as many as 100,000 bird carcasses washed up on shore along the Pacific Coast from California to Washington. Although much of the mystery of the die-off remains, researchers are starting to untangle the puzzle.
Ecologist Julia Parrish of the University of Washington in Seattle says the deaths may be due to weather. Early in the year, weak winds failed to stir the Pacific as much as usual. That kept deep, nutrient-rich water from reaching the surface—an upwelling that serves as "a kind of turbo boost to the ecosystem," Parrish says. Without it, the food chain suffered: Plankton went missing, as did the little fish that ate them.
Birds couldn't just pick up and go elsewhere, because they were breeding. The stress caused many seabirds to mate much later than usual or not at all, and those that tried to raise young were faced with a grim quandary, Parrish says: "Do you stay and defend your chick from predators, or do you leave and get food? A lot of them waited too long." At a time when the birds should have been "fat and sassy, in the best body condition," she says, many ended up dead.
Why the winds were light is still a mystery. "If we are experiencing a new weather or climate phenomenon along the Pacific Coast," Parrish says, "we will see dramatic changes . . . it keeps me up at night." —Elise Kleeman