h*h 发帖数: 27852 | 1 【 以下文字转载自 ChinaNews 讨论区 】
发信人: hsh (三胡), 信区: ChinaNews
标 题: 气温变暖也许是好事?
发信站: BBS 未名空间站 (Wed Nov 9 14:33:32 2011, 美东)
如果现在是冰河期的话,地球能支持多少人?
30亿?40亿死掉?
20亿?50亿死掉?
Next Ice Age Delayed by Global Warming, Study SaysChristine Dell'Amore
National Geographic News
September 3, 2009
Humans are putting the brakes on the next ice age, according to the most
extensive study to date on Arctic climate change.
The Arctic may be warmer than it's been in the past 2,000 years—a trend
that is reversing a natural cooling cycle dictated by a wobble in Earth's
axis.
Previously, researchers had looked at Arctic temperature data that went back
just 400 years. (See photos of how climate change is transforming the
Arctic.)
That research showed a temperature spike in the 20th century, but it was
unclear whether human-caused greenhouse gas emissions or natural variability
was the culprit, noted study co-author Gifford Miller of the Institute of
Arctic and Alpine Research at the University of Colorado, Boulder.
By looking even farther back in time, Miller and colleagues' newest study
reveals that the 20th century's abrupt warming may have in fact interrupted
millennia of steady cooling.
It's "pretty clear that the most reasonable explanation for that reversal is
due to increasing greenhouse gases," Miller said.
The researchers' computer climate models dovetails with field data such as
sediment cores and tree rings, which "really … solidifies our understanding
," he said.
Eventually Earth will slip again into the pattern of cyclical ice ages,
Miller added, but it may be thousands of years before that happens.
Ice Age, Interrupted
Earth's angle toward the sun changes due to a natural 26,000-year-long
wobble, which causes the planet to spin on is axis like an unstable top, so
that a line drawn from the axis would trace a cone in the sky.
The wobble causes Earth to make its closest pass by the sun in different
months over the long term. For the past 7,000 years, Earth has passed
closest to the sun in January.
This means less sunlight has been hitting the Arctic during its summertime,
so the region should be cooling.
To estimate past temperatures, the research team looked at Arctic lake
sediments and at previously published data of glacial ice cores and tree
rings.
The team also examined a computer model of global climate based at the
National Center for Atmospheric Research in Colorado.
Miller and colleagues found that the wobble in Earth's tilt causes Arctic
temperatures to drop by about 0.36 degree Fahrenheit (0.2 degree Celsius)
every thousand years during a cooling phase.
But human-caused global warming overwhelmed that gradual cooling in the mid-
1990s, shooting temperatures up by about 2.5 degrees Fahrenheit (1.4 degrees
Celsius) over the course of a few decades.
In fact four of the five warmest decades in the past 2,000 years occurred
after 1950, according to the study, which will be published tomorrow in the
journal Science.
Ecologist Syndonia Bret-Harte said she has seen the effects of climate
change firsthand during her research on the changing Alaskan tundra.
The new study "doesn't seem that surprising, but it's good to confirm what
researchers were already thinking," said Bret-Harte, of the Institute of
Arctic Biology at the University of Alaska, Fairbanks.
Global Warming Amplifiers
The effects of climate change are powerfully amplified in the Arctic, which
has been heating up faster than anywhere else on Earth.
That's because Arctic temperatures are greatly impacted by melting from both
summer sea ice and permafrost, or frozen soil, experts say.
Summer Arctic sea ice, which hit a record low in 2007, will probably have
dissolved completely by 2030.
Without swaths of white ice to reflect sunlight back into the atmosphere,
those rays will instead be absorbed into the darker oceans—speeding up the
region's warming.
And melting permafrost is already starting to release carbon dioxide and
methane, two potent greenhouse gases that have long been trapped underground
.
"It's pretty straightforward that amplification will continue in the future.
There will be direct impacts in the Arctic," study co-author Miller said.
"The big issue is, when you melt ice, the sea level rises—that's a global
issue, and that has major impacts."
Bret-Harte agreed that the amplifying effects are "going to continue until
summer sea ice is gone—there's no way to reverse the trend in the short
term."
But that doesn't mean people shouldn't act, she said.
"Realistically we're looking at a warmer world, and there are two questions:
How do we adapt to that as humans but [also] slow down the pace of [climate
] change? The faster it is, the harder it is to adapt." |
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