Expanding glaciers and ice cover spreading across Greenland began driving the Norse settlers out.
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This makes it hard to say how fast the summer ice cover will continue to shrink.
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According to WWF researchers, sea ice cover has declined by about 40% over the last quarter century.
Ice age is an important indicator of the health of the ice cover.
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September ice cover of less than 1m km2 could be normal within decades.
ECONOMIST: Summer ice in the Arctic Ocean is vanishing rapidly
For example, at higher altitudes only certain plant and animal species can survive under long periods of snow and ice cover.
This has allowed scientists to retrieve information about the Arctic Ocean region's gravity field, its surface circulation, and the thickness of its sea-ice cover.
More recently, his techniques have begun to reveal how the changing ice cover might affect the interaction between the Arctic Ocean and the atmosphere.
When combined with data on past sea levels, these give an estimate of global temperatures and sea-ice cover for the past three million years.
Martin Sommerkorn from the WWF International Arctic Program believes that the changes in sea-ice cover in the region are likely to increase global temperatures further.
Ice cover loss can influence winds and precipitation on other continents, possibly leading to less rain in the western United States and creating more in Europe.
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Arctic sea ice cover grows each winter as the sun sets for several months, and shrinks each summer as the sun rises higher in the northern sky.
What is more, the extent of sea ice cover influences the abundance of krill and the fish species that eat them - both food sources for the penguins.
Although few humans live in the Arctic, the disappearance of this ice cover can have effects far beyond the few residents and the wildlife of this harsh region.
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These days, thanks to global warming and a receding ice cover, the voyage is easier to complete, says explorer James Delgado, author of Across the Top of the World.
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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Climate change models of Arctic sea ice cover in September, the month when ice is usually at its minimum, suggest an average loss of 2.5 percent of ice cover per decade from 1953 to 2003.
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.
Earlier this month NSICD scientists reported that winter sea ice cover in the Arctic was just 14.7 million square kilometers (5.7m square miles) -- slightly better than the all-time low 14.5m square kilometers (5.6m square miles) in 2006 -- but well short of the 15.7m average for 1979-2000.
In theory, climate models should help tease out which of these indirect effects is playing the biggest role, and also say how much of the decline in ice cover can be assigned to natural variability and how much to feedback loops in which a little warming leads to a lot more.
ECONOMIST: Summer ice in the Arctic Ocean is vanishing rapidly
The Greenland ice sheets cover 1.7m square km an area only a little smaller than Mexico and the surface of the ice rises to an altitude of 3km.
The programme aims to maintain a network of at least 3, 000 Argo floats, over all ocean areas without ice-cover, to study ocean variability in the long term.
With 102 holes drilled so far, hundreds of measurements have been made of ice thickness and snow cover over the 243km covered to date.
Of these freshwater resources, about 24 million km3 or 70% is in the form of ice and permanent snow cover in mountainous regions, the Antarctic and Arctic regions.
Weather is caused by disturbances within the atmosphere, but climate is controlled by external influences, such as the distribution of oceans and continents, the extent of ice and snow-cover, variations in the amount of energy from the sun, and changes in the chemical composition of the atmosphere.
By 1996 it had become a new flavour of Ben and Jerry's ice cream and the title on a Newsweek cover.
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Weather stations, ocean measurements, decreases in snow cover, reductions in Arctic sea ice, longer growing seasons, balloon measurements, boreholes and satellites all show results consistent with the surface record of warming.
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"Even clad in full winter gear, with ice-axes, winter boots and full waterproof body cover, it was a struggle, " said Mr Rodwell.
"It means there is more light penetrating through the ice - that depends to a high degree on the snow cover but once it has melted the light can get through, " Dr Gerland said.
Added to the general atmospheric warming in the region, the researchers also describe an amplification process whereby reduced snow cover on the surrounding tundra and less sea-ice in the Arctic Ocean push up temperatures still further.
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