20. Global Warming Leaves Its Marks

Sixteen places where global warming is apparent.

1. Africa: Ice fields on the mountains near the equator are shrinking and could vanish within 20 years.

2. Alpine glaciers: The Alps could lose between 80 and 100 percent of their glaciers by the end of this century.

3. Antarctica: Winter air temperatures over Antarctica have risen by more than 2 degrees Celsius since the 1970s.

4. Greenland and Antarctica: 20 billion tons of water flows into oceans every year because of runoff from ice sheets in these two polar areas. Greenland's ice is now melting three times as quickly as it was just five years ago.

5. The Arctic: Giant cracks larger in total area than the British Isles appeared in August in the Arctic sea ice.

6. Western United States: Large forest fires have occurred more frequently as spring temperatures have increased. The dry season grew longer, and summers got hotter.

7. Northern Bering Sea: Whales are moving farther north as temperatures warm.

8. Sweden: The country plans to be the world's first oil-free economy within 15 years.

9. Britain: Scientists report that 80 percent of more than 300 animals studied have extended the northern boundary of their habitats. Also, episodes of extreme rain have become more frequent in parts of the United Kingdom over a 40-year period.

10. Europe: Spring arrives an average of six to eight days earlier than in the 1970s. Seventy-eight percent of 542 plant species studied flowered and fruited earlier in the year. Migratory birds were flying home to Northern Europe earlier in time for the beginning of spring.

11. Northern Siberia: As lakes in the permafrost zone of northern Siberia thaw, they are releasing methane—a potent greenhouse gas. The carbon in the methane had been sequestered in the permafrost for more than 40,000 years.

12. Atlantic and Pacific oceans: Average sea surface temperatures in the tropical Atlantic and Pacific oceans have risen by 1.2 and 0.58 degrees Fahrenheit in the 20th century; the number of category 4 and 5 hurricanes worldwide has nearly doubled over the past 35 years.

13. Pacific: The flow of air currents that fuels Pacific trade winds and modulates the weather from South America to Southeast Asia may be weakening.

14. South America: Glaciers in the region are melting so fast that some are expected to disappear within 15–25 years. The resulting water shortage would jeopardize people and food supplies in Colombia, Peru, Chile, Venezuela, Ecuador, Argentina, and Bolivia.

15. Himalayas: Snow and ice cover in the eastern Himalayas has shrunk by about 30 percent since the 1970s. The melt-off could cause flooding.

16. China: A November report predicts that the coal-powered, populous country will surpass the United States in 2009 as the world's biggest emitter of climate-warming carbon dioxide.

Josie Glausiusz

35. Melting Permafrost May Rev Up Global Warming

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

52. Storms May Be Getting Worse

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

61. Ancient Rain Settles Sierra's Age

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

81. Tut Jewel Formed by Asteroid Impact

The central jewel in King Tutankhamen's pectoral gear may have been literally out of this world—the result of an asteroid that exploded above the Sahara—according to Mark Boslough, a researcher at Sandia National Laboratories. In 1998 researchers elsewhere determined that Tut's jewel wasn't chalcedony but an unusual type of desert glass. Boslough, who was part of a team that created a computer simulation to predict what would happen when comet Shoemaker-Levy hit Jupiter, was later enlisted to figure out if the gem was meteoric in origin.

Boslough used Sandia's Red Storm supercomputer to ask what conditions would be required to melt Saharan sand into glass. The winning scenario: a 400-foot-wide stony asteroid that slammed into the air at 12 miles a second and exploded. For 20 seconds the resulting fireball would have been hot enough to melt quartz on the ground, creating glass that can still be found in the desert. Ancient Egyptians might have rightly recognized such ornaments as more precious than gold.

Michael Abrams

82. Secret Lakes Lie Under Polar Ice

A decade after Russian and British researchers announced the discovery of Lake Vostok, an enormous body of water more than two miles beneath the permanent ice sheet of Antarctica, two independent teams of scientists have evidence of other large subglacial lakes and rivers, and perhaps an entire watershed.

Robin Bell of Columbia University had long suspected that a slight depression on the surface of the ice indicated two additional, very large underground lakes, but this year she confirmed their existence with high-resolution measurements. The lakes, called 90°E and Sovetskaya, are each roughly the area of Lake Okeechobee in Florida; in Antarctica, only Lake Vostok is larger.

In April a group led by climate physicist Duncan Wingham of University College London announced the discovery of more subglacial lakes. They are linked by rivers that form when melting ice expands the lakes, increasing pressure under the ice cap and causing underground channels of water and mud to squirt out.

Instead of existing largely as separate entities, as experts had believed, the roughly 150 known lakes (and possibly thousands yet to be found) are likely part of a vast watershed, with streams periodically shooting from one lake to the next. While biologists long to sample this underground world for traces of life that may have been isolated for millions of years, the new evidence raises concerns that drilling for samples could contaminate the entire ecosystem.

Jeffrey Winters

90. Drillers Tap into Foundation of Earth's Crust

In April geologists reported that they had successfully drilled into the bottom layer of the ocean's crust for the first time—and so have come a step closer to understanding how the foundation of the world takes shape.

New crust forms at midocean ridges where the sea floor spreads apart. Lava leaking from the ridges creates the crust's upper layer; beneath that lies a second layer, composed of the fossilized channels that once piped molten rock to the ridges. The formation of the lowermost crust, made up of a dark, magnesium-rich rock called gabbro, is still largely a mystery, one that holds the key to the workings of the magma source that feeds the whole process.

Douglas Wilson, a geophysicist at the University of California at Santa Barbara, and his colleagues traveled 500 miles west of Costa Rica to an area of ocean floor that formed 15 million years ago. There they found just the right piece of crust—not too hot, not too thick, and not too crumbly—to drill down to the gabbro. In 2006 they released their findings: After drilling through nearly a mile of sediment and crust, they finally hit the gabbro layer for the first time. Wilson hopes to drill deeper into this third layer by 2009. Then he will truly plumb Earth's deep secrets.

Anne Sasso