Say goodbye to the world’s tropical glacie

问题：

Say goodbye to the world’s tropical glaciers and ice caps. Many will vanish within 20 years. When Lonnie Thompson visited Peru’s Quelccaya ice cap in 1977, he couldn’t help noticing a school-bus-size boulder that was upended by ice pushing against it. Thompson returned to the same spot last year, and the boulder was still there, but it was lying on its side. The ice that once supported the massive rock had retreated far into the distance, leaving behind a giant lake as it melted away.
Foe Thompson, a geologist with Ohio State University’s Byrd Polar Research Center, the rolled-back rock was an obvious sign of climate change in the Andes Mountains. "Observing that over 25 years personally really brings it home," he says. "Your don’t have to be a believer in global warming to see what’s happening."
41. Thawed ice caps in the tropics.
Quelccaya is the largest ice cap in the tropics, but it isn’t the only one that is melting, according to decades of research by Thompson’s team. No tropical glaciers are currently known to be advancing, and Thompson predicts that many mountaintops will be completely melted within the next 20 years.
42. Situation in areas other than the tropics.
The phenomenon isn’t confined to the tropics. Glaciers in Europe, Russia, new Zealand, the United States, and elsewhere are also melting.
43. The worsening effects of global warming.
For many scientists, the widespread melt-down is a clear sign that humans are affecting global climate, primarily by raising the levels of carbon dioxide and other greenhouse gases in the atmosphere.
44. Receding ice caps.
That’s not to say that glaciers, currently found on every continent except Australia, haven’t melted in the past as a result of natural variability. These rivers of ice exist in a delicate balance between inputs (accumulating snow and ice) and outputs (melting and "calving" of large chunks of ice). Over time, the balance can tilt in either direction, causing glaciers to advance or retreat. What’s different now is the speed at which the scales have tipped. "We’ve been surprised at how rapid the rate of retreat has been," says Thompson. His team began mapping one of the main glaciers flowing out of the Quelccaya ice cap in 1978, using satellite images and ground surveys.
45. Thinning ice cores.
And its’ not just the margin of the ice cap that is melting. At Quelccaya and Mount Kilimanjaro, the researchers have found that the ice fields are thinning as well. Besides mapping ice caps and glaciers, Thompson and his colleagues have taken core samples from Quelccaya since 1976, when the ice at the drilling location was 154 meters thick.
Thompson and his colleagues have also drilled ice cores from other locations in South America, Africa, and China. Trapped within each of these cores is a climate record spanning more than 8,000 years. It shows that the past 50 years are the warmest in history.
The 4-inch-thick ice cores are now stored in freezers at Ohio State. On the future, says Thompson, that may be the only place to see what’s left of the glaciers of Africa and Peru.
[A] The latest report from the Intergovernmental Panel on Climate Change, prepared by hundreds of scientists and approved by government delegates from more than 100 nations, states. "There is new and per evidence that most of the warming observed over the last 50 years is attributable to human activities." The report, released in January, says that the planet’s average surface temperature increased by about 0. 6℃ during the 20th century, and is projected to increase another 1.4℃ to 5.8℃ by 2100. That rate of warming is "with-out precedent during at least the last 10,000 years," says the IPCC.
[B] Alaska’s massive Bering and Columbia Glaciers located in nontropical regions, for example, have receded by more than 10 kilometers during the past century. And a study by geologists at the University of Colorado at Boulder predicts that Glacier National Park in Montana, under the influence of melting, will lose all of its glaciers by 2070.
[C] For example, about 97 per cent of the planet’s water is seawater. Another 2 per cent is locked in icecaps and glaciers. There are also reserves of fresh water under the earth’s surface but these are too deep for us to use economically.
[D] For example, Africa’s Mount Kilimanjaro in tropical areas has lost 82 percent of its ice field since it was first mapped in 1912. That year, Kilimanjaro had 12.1 square kilometers of ice. By last year, the ice covered only 2.2 square kilometers. At the current rate of melting, the snows of Kilimanjaro that Ernest Hemingway wrote about will be gone within 15 years, Thompson estimates. "But it probably will happen sooner, because the rate is speeding up."
[E] "I fully expect to be able to return there in a dozen years or so and see the marks on the rock where our drill bit punched through the ice," says Thompson. If that happens, it will mean that a layer of ice more than 500 feet thick has vanished into thin air.
[F] The glacier, Qori Kalis, was then retreating by 4. 9 meters per year. Every time the scientists returned, Qori Kalis was melting faster. Between 1998 and 2000, it was retreating at a rate of 155 meters per years (more than a foot per day), 32 times faster than in 1978. "You can almost sit there and watch it move," says Thompson.