The Year in Science: Environment

Siberian methane, the recovering ozone layer, hurricane history in tree rings, and more.

Monday, January 30, 2006

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

Arctic Waterfowl Sanctuary Dries Up

The Canada geese and other waterfowl that wing north every spring may soon face some disorienting surprises. Their Arctic summer home is changing. A report released in June reveals that the freshwater lakes are shrinking, some even draining completely.

Permafrost normally forms an impermeable layer under the summer lake water, containing it the way a bowl holds soup. But the Arctic has been growing warmer for the last three decades, and the permafrost is defrosting. That allows lake water to drain into the subsurface soils, according to a team of scientists led by Laurence C. Smith, a UCLA geographer, and Larry Hinzman, a hydrologist at the University of Alaska in Fairbanks. In short, surface water is becoming groundwater. "The effects," says Hinzman, "are dramatic, not subtle."

After comparing recent satellite images of over 10,000 large Arctic lakes with images from the 1970s, Smith and Hinzman concluded that the total number had declined by 11 percent, with 125 of them vanishing completely. That 85 percent of the disappearances occurred within 124 miles of the continuous-permafrost boundary suggests that warming permafrost is the cause. The defrosting is likely to have a cascading effect, concentrating migratory birds that feed at the freshwater lakes into smaller areas and making some species more vulnerable to predators like foxes. At the same time, the change in adjacent vegetation will affect migratory mammals, like caribou. "The Arctic," says Smith, "is our canary in the mine."  —Michael W. Robbins

Poisons Permanently Harm Male Offspring And Later Generations

For the first time, environmental toxins have been shown to damage several generations of offspring—without changing a single gene sequence.

The discovery occurred when Michael Skinner, a molecular and cellular biologist at Washington State University, injected the chemicals vinclozolin, a fungicide used on wine grapes, and methoxychlor, a pesticide, into pregnant rats. Males born to those rats (and exposed to toxins in the womb) produced sperm that swam slowly and died early. The surprise came when those males fathered offspring: Ninety percent of their sons had the same problem. The pattern repeated in the grandsons and in the great-grandsons.

Genetic mutations, such as those caused by radiation and certain chemicals, do not show such high heritability. "There was no mechanism previously known that would allow this to occur," Skinner says. Instead, he says, epigenetics is the culprit: What changed was not what the genes say but what they do. The toxins permanently altered the way the rat DNA was expressed, perhaps by altering the chemical tags that some genes carry. "It's not naked DNA that you inherit," explains Emma Whitelaw of the Queensland Institute of Medical Research in Australia, whose work was the first to show that expression patterns can be heritable in animals. 

Skinner says his study, published in June, provides the first direct evidence that the environment can alter gene expression for generations. So far his results apply only to rats. But future generations of humans may come to wish that today's toxicologists had started thinking about them now.  —Jessica Ruvinsky

Sea Level Rises 50 Percent Faster

For sinking cities like New Orleans and Venice, ocean warming trends will make a bad situation even worse. When ice sheets melt and oceans heat up, the sea level rises. A fleet of satellites has been monitoring the situation, and in July Steve Nerem, a geophysicist at the University of Colorado at Boulder, and his colleagues  pulled together the evidence. Bottom line: Oceans are rising about 50 percent faster than in previous decades.

The sea-level readings come from NASA satellites called TOPEX/Poseidon and Jason-1, which map the oceans every 10 days. On average, sea level has risen more than a tenth of an inch per year over the last 12 years. That's a sizable increase over the rate of the previous 50 years, as estimated by tide gauges around the world. Nerem cautions that it's too soon to pin the result on global warming; it could be due to regular changes in ocean climate. "It's hard to know whether this reflects a long-term change or a short-term change," he says. It will take another 10 to 15 years to settle the case. Still, the increase is about what's predicted by computer models of global climate.

According to calculations by other scientists, roughly half the rise comes from the thermal expansion of the oceans as they warm. Melting mountain glaciers and polar ice are also adding to new heights. And climatologists suspect that the ice sheets of Greenland and Antarctica are involved, although exactly how much is not known. These ice sheets have been sliding ever faster toward the sea, but research this year showed that parts of Antarctica are actually getting thicker. That means the overall contribution to sea level "is still a little fuzzy," says glaciologist Richard Alley of Pennsylvania State University. Finding out how ice sheets are behaving is crucial, Alley and others say: The ice of Antarctica and Greenland contains enough water to raise the sea level by more than 200 feet.  —Erik Stokstad

Scientists Warm To A New Climate Model

Skeptics who doubt that greenhouse-gas emissions produced by humans cause global warming often point to data from satellites and weather balloons that indicate the troposphere—the lowest 10 miles or so of the atmosphere—has actually been cooling since 1979. But extracting trends from the information recorded by the dozen satellites and thousands of weather balloons launched over the years is a difficult business.

 "There are a lot of things that can go wrong with these soundings," says Steven Sherwood, an atmospheric scientist at Yale University. In August Sherwood and his collaborators published the results of a study that corrected for the heating effect of direct sunlight on older weather balloons. Another study adjusted for the gradual drift of satellite orbits, and a third took the revised satellite data and compared them with 19 existing global climate models. The conclusion: The troposphere is warming after all.

The three papers remove a major stumbling block to a scientific consensus, says Benjamin Santer of Lawrence Livermore National Laboratory, lead author of the climate model study. "Will all of this make a difference to the real dyed-in-the-wool climate skeptics? I doubt it," he says. "Will it make a difference to the scientific community and to the general public in what they might think about the nature and causes of climate change? I hope so." —Alex Hutchinson

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