The arctic is highly sensitive to climate change. While rising temperatures could wreak havoc with northern communities and ecosystems, shrinking sea ice and permafrost threaten to accelerate climate change with global impacts.

Sea Ice
During the fall and winter, a huge portion of northern oceans freezes, forming a one- to three-metre-thick layer of sea ice. In the spring and summer much of this ice melts again. Sea ice provides shelter and transportation for seals, walrus, arctic foxes, polar bears and Inuit. The underside of the ice also provides a surface on which algae can flourish, forming the base of a rich food chain which supports cod, char, beluga and narwhal.

Although large annual fluctuations and the remoteness of the arctic make changes in sea ice difficult to measure, many independent studies have shown that arctic sea ice is shrinking. Records from satellite and submarine data show that sea ice area has been decreasing by three to five per cent per decade since the 1950s. The year 2002 had less sea ice than any previous year since detailed observations began 50 years earlier.

"It is likely that sea ice extent will continue to decline over the 21st century as the climate warms," says Mark Serreze, of the National Snow and Ice Data Center in Boulder, Colorado (NASA, Dec 7,2002). "We may see an approximate 20 per cent reduction in the annual mean sea ice by 2050, and by then we might be approaching no ice at all during the summer months."

Permafrost
Permanently frozen soil and rock lies beneath almost 25 per cent of the northern hemisphere in layers up to 1,400 metres thick. In much of Canada and northern Asia, a thin near-surface layer melts during summer but the frozen ground beneath provides a firm foundation year round.

Many industrial structures, like this mining equipment on Baffin Island, may collapse as the supporting permafrost thaws.

When permafrost melts, the soil loses its supporting network of ice crystals. This causes the ground above to collapse, setting off slumps and landslides which can destabilize buildings, roads and other infrastructure. Although much of the arctic is sparsely inhabited, there are large mines, oilfields, pipelines, airstrips and - in Russia - a nuclear power station, all resting on permafrost. Most of these structures, designed after the 1940s, were engineered to rely on the stability of the permafrost beneath. As the ground shifts, they can collapse, spilling hazardous chemicals into the environment and sometimes threatening human lives.

Permafrost will continue to melt slowly over centuries as the arctic warms, retreating closer and closer to the pole. Unfortunately, its retreat could also generate billions of tonnes of additional greenhouse gases.

This frozen landscape could become a huge source of methane, accelerating climate change.

Snowballing effects
Permafrost and sea ice both have cooling effects on the climate. Because sea ice is white, it reflects light away from the earth's surface, keeping it cool. Less sea ice means more heat will be absorbed by the ocean, which further prevents sea ice formation and exacerbates climate change.

Meanwhile, permafrost serves as an enormous 'freezer' filled with undecayed plant matter, one of the largest carbon reservoirs on earth. As permafrost melts, that plant matter starts to rot, releasing huge quantities of methane - a greenhouse gas 21 times more potent that carbon dioxide. Many permafrost zones contain enough plant matter to keep generating methane for centuries, once warming begins.

Collapsing Ice Sheets
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