Satellite data show that arctic late-summer ice has been in decline for about 25 years.
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This makes it hard to say how fast the summer ice cover will continue to shrink.
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But it is also possible that one or other of them will win through, with a significant effect on this year's summer ice.
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As summer ice in the Arctic has declined in recent years, the area has become the subject of intense interest from oil and gas companies.
Last month, scientists at the US National Snow and Ice Data Center said Arctic summer ice was almost 30% below the long-term average, and predicted 2007 would show the lowest ice cover on record.
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Since about 2002, the satellite data record has indicated that the downward trends in summer ice cover have accelerated, with the implication that a seasonally ice-free Arctic ocean may be realized sooner than projected by our most advanced climate models.
It's also important to remember that when people talk about decreases in sea ice, they're usually referring to summer sea ice.
They also look very similar to the simulations coming out of Piomas (Pan-Arctic Ice-Ocean Modelling and Assimilation System), an influential computer model that has been used to estimate Arctic sea-ice volume and which has been the basis for several predictions about when summer sea ice might disappear completely.
Many scientists expect summer sea ice to disappear in a matter of decades.
The area is now more likely to become open water each summer, bringing forward the potential date when the summer sea ice will be completely gone.
Absorption is particularly fast in cold water so the Arctic is especially susceptible, and the recent decreases in summer sea ice have exposed more sea surface to atmospheric CO2.
The general warming trend -- 13 of the warmest years have occurred in the 15 years since 1997 -- was highlighted by summer sea ice melt in the Arctic.
The term describes the moment at which the planet shifts from one environmental state to another: in this case, from an Arctic with summer sea ice to one without it.
Reducing soot (and also ozone, an industrial pollutant that acts as a greenhouse gas) would not stop the summer sea ice disappearing, but it might delay the process by a decade or two.
The study, published in the latest edition of the journal Geophysical Research Letters, found that the actual rate at which summer sea ice had shrunk per decade during the past 50 years was more than three times faster than an average of 18 of the most highly regarded climate simulations.
According to a recent paper by Francis and Vavrus in Geophysical Research Letters, the preferential warming of the Arctic, with a concomitant decline in late-summer sea ice, results in a more meandering jet stream, which is why Sandy shifted westward, rather than being shoved out to sea by the normally strong westerlies associated with the jet.
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For instance, sea ice is predicted to increasingly shrink as a result of climate change: the late-summer Arctic sea ice may vanish almost entirely by the middle of the century, triggering unprecedented maritime challenges, with an increase in shipping and oil and gas exploration in high-latitude waters previously covered in ice.
Ten years ago scientists reckoned that summer sea-ice would be gone by the end of this century.
Very few scientists think Greenland would be stable in an Arctic with little or no summer sea-ice, and opinion is split as to whether it is past its tipping point already.
One theory is that the summer sun melts ice on the surface of the glacier which creates pools of water which then flow into moulins -- narrow tubular shafts in the glacier.
"This suggests that current model projections may in fact provide a conservative estimate of future Arctic change, and that the summer Arctic sea ice may disappear considerably earlier than IPCC projections, " said NSIDC's Julienne Stroeve who led the study.
For a number of reasons, computer models with added atmospheric carbon dioxide preferentially warm the mid-and high-latitude land areas of the northern hemisphere that are ice-free, which also enhances summer melting of the relatively shallow ice in the Arctic Ocean.
The analysis produced a summer Arctic sea-ice minimum extent of 6.9 million sq km.
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The ban effectively postpones any work in Alaska until at least next summer, as sea ice prevents winter drilling.
Estimates range from 2013 terrifyingly soon to 2050 for the first year when the Arctic is free of ice in summer.
Every summer an extra area of ice six times the size of California has been disappearing.
This past summer, the Arctic sea ice dwindled to its second lowest level.
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Warming Arctic seas and a marked decline in sea ice during the summer months made it likely, they concluded, that numbers would fall by one third within three generations (45 years).
By the mid-2030s, scientists have predicted that the Arctic will be ice-free for at least one month of every summer, which will expand to two-to-three ice-free months by around mid-century.
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