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Previous positive predictions about the ozone-layer recovery by 2040 have now received a serious coup: a new study suggests that by 2040 there will be no ice left for polar bears.
Already considered among the most endangered species of animals in the world, the polar bears are again threatened by the conclusions of a new study, published in scientific journal Geophysical Research Letters on Tuesday, which indicates that the Arctic pole will not be a barren desert of ice by this century’s half, but a warm ocean.
The North Pole is already significantly warmer than the South Pole because it lies at sea-level in the middle of an ocean (which acts as a reservoir of heat), rather than at altitude in a continental land mass.
Winter (January) temperatures at the North Pole can range from about −43°C (−45篎) to −26°C (−15°F), perhaps averaging around −34°C (−30篎). Summer temperatures (June, July and August) average around freezing point (0°C, 32°F).
The sea ice at the North Pole is typically around two or three meters thick, though occasionally the movement of floes exposes clear water. Some studies have indicated that the average ice thickness has decreased in recent years due to global warming.
One of these studies is the one recently unveiled in the Geophysical Research Letters.
\"The effects of greenhouse warming are starting to rear their ugly head,\" said Mark Serreze, a scientist at the National Snow and Ice Data Center at the University of Colorado in Boulder.
Previous studies have shown that the Arctic water fails to freeze back in winter, a natural process that has been going on for millennia. According to scientists, 2006 is the second year in a row when the sea ice covering the Arctic Ocean didn't manage to reach its normal winter size, thus leading to an overall shrinking. Climate experts say that this is due to rapid global climate change and will cause a serious expansion of open water in the upcoming summer.
An independent team at the University of Illinois has already proven in March that the ice retreat in September was the biggest measured since 1979, when satellites began routinely monitoring the region in and is also probably the biggest in the last 100 years.
Moreover, as the Arctic area enters its six months of daylight, this condition is likely to be amplified by the ice turning to water because of the water absorption of the sunlight that ice would otherwise reflect.
Mark Serreze, a scientist at the National Snow and Ice Data Center in Boulder, Colorado, which monitors the region using satellites, published a previous study in spring 2006, where he warned about the possibility of seeing the Arctic ice disappearing by 2070.
Now, the same scientist revises its forecast and predicts the ice melting sooner: by this century’s half.
Last month, the sea that was frozen covered an area that was two million sq km less than the historical average.
\"That's an area the size of Alaska,\" said leading ice expert Mark Serreze.
\"We're no longer recovering well in autumn anymore. The ice pack may now be starting to get preconditioned, perhaps to show very rapid losses in the near future,\" the University of Colorado researcher added.
On 14 September, the sea ice reached its minimum extent in 2006, making the current year the fourth lowest on record in 29 years of satellite record-keeping, but below the all-time record registered last year.
Marika Holland, a scientist at the National Center for Atmospheric Research, projects a slow, steady decline of Arctic ice as global warming continues, with a dramatic \"tipping point\" in about two decades.
\"The ice is actually quite stable until 2025 and then boom, it goes,\" Holland told the fall meeting of the American Geophysical Union in San Francisco.
Simulation on supercomputers has also proven that the observations collected by satellites are in direct connection with the theoretical modeling of climate evolution.
As the Arctic area enters its six months of daylight, this melting is likely to be amplified by the ice turning to water because of the water absorption of the sunlight that ice would otherwise reflect.
\"As the ice retreats, the ocean transports more heat to the Arctic and the open water absorbs more sunlight, further accelerating the rate of warming and leading to the loss of more ice,\" explained Dr Marika Holland.
\"This is a positive feedback loop with dramatic implications for the entire Arctic region.\"
Eventually, she said, the system would be \"kicked over the edge\", probably not even by a dramatic event but by one year slighter warmer than normal. Very rapid retreat would then follow.
The melting of the ice from the North Pole brings some good and bad effects. Bad effects mean the disappearing of the natural habitat for a few endemic species, like the polar bear. Good effects are the opening of the maritime routes and the economic boom for Canada and Russia.
On a global scale, the Earth would lose a major reflective surface and so absorb more solar energy, potentially accelerating climatic change across the world.
\"We don't think that state has existed for hundreds of thousands of years; this is a dramatic change to the Arctic climate system,\" Dr Holland told the BBC.
\"My gut feeling is that it might be around the year 2030 that we really see a rapid decline of that ice. Now could it occur sooner? It might well. Could it occur later? It might well.
\"It depends on the aspects of natural variability in the system. We have to remember under greenhouse warming, natural variability has always been part of the picture and it always will be part of the picture.\" |
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发表于 2006-12-13 15:16:30