Climate Change in The Arctic - Modelling, History, and Predictions of Sea Ice

Modelling, History, and Predictions of Sea Ice

See also: Arctic sea ice ecology and history

Computer models predict that the sea ice area will continue to shrink in the future, although recent work has called into question their ability to accurately predict sea ice changes. Current climate models frequently underestimate the rate of sea ice retreat. In 2007 the IPCC reported that "the projected reduction is accelerated in the Arctic, where some models project summer sea ice cover to disappear entirely in the high-emission A2 scenario in the latter part of the 21st century.″ There is currently no scientific evidence that a seasonally ice-free Arctic Ocean existed anytime in the last 700,000 years, although there were periods when the Arctic was warmer than it is today. Scientists are studying possible causal factors such as direct changes resulting from the greenhouse effect as well as indirect changes such as unusual wind patterns, rising Arctic temperatures, or shifting water circulation (such as increasing inflows of warm, fresh water to the Arctic Ocean from rivers.)

According to the Intergovernmental Panel on Climate Change, "warming in the Arctic, as indicated by daily maximum and minimum temperatures, has been as great as in any other part of the world." Reduction of the area of Arctic sea ice means less solar energy is reflected back into space, thus accelerating the reduction. Studies have shown that recent warming in the polar regions was due to the net effect human influence; the warming radiative forcing of greenhouse gases is only partially offset by the cooling effect of ozone depletion. Reliable measurement of sea ice edge begin within the satellite era in the late 1970s. Before this the region was less well monitored by a combination of ships, buoys and aircraft. On top of the long-term negative trend in recent years, attributed to global warming, there is considerable interannual variation. Some of this variation may be related to effects such as the arctic oscillation, which may itself be related to global warming; some of the variation is essentially random "weather noise".

The Arctic sea ice September minimum extent reached new record lows in 2002, 2005, 2007 (39.2 percent below the 1979–2000 average) and 2012. (Roughly 50% below the 1979-2000 average) In 2007, Arctic sea ice broke all previous records by early August—a month before the end of melt season, with the biggest decline ever in Arctic sea ice minimum extent, more than a million square kilometers. In the first time in human memory, the fabled Northwest Passage opened completely. The dramatic 2007 melting surprised and concerned scientists.

From 2008 to 2011, Arctic sea ice minimum extent was higher than 2007, but it did not return to the levels of previous years. In 2012 however, the 2007 record low was exceeded in late August with 3 weeks still left in the melt season. A few days later, as August ended, the sea ice extent was below 4 million square kilometers for the very first time on record. It continued to fall, going below 3 and half million square kilometers by mid September, over 600,000 square kilometers lower than the 2007 record low. It bottomed out on 16 September 2012 at 3.41 million square kilometers (1.32 million square miles), or 760,000 square kilometers (293,000 square miles) below the previous low set on 18 September 2007.

The sea ice thickness field, and accordingly the ice volume and mass, is much more difficult to determine than the extension. Exact measurements can be made only at a limited number of points. Because of large variations in ice and snow thickness and consistency air- and spaceborne-measurements have to be evaluated carefully. Nevertheless the studies made support the assumption of a dramatic decline in ice age and thickness. The Catlin Arctic Survey reported an average thickness of 1.8 meters across the northern Beaufort Sea, an area that had traditionally contained older, thicker ice. Another approach is to simulate ice growth, melting and drift numerically in an integrated ocean-atmosphere model with input parameters fine tuned to fit model output to known thickness and extent data.

The rate of the decline in entire arctic ice coverage is accelerating. From 1979–1996, the average per decade decline in entire ice coverage was a 2.2% decline in ice extent (i.e., area with at least 15% sea ice coverage) and a 3% decline in ice area. For the decade ending 2008, these values have risen to 10.1% and 10.7%, respectively. These are comparable to the September to September loss rates in year-round ice (i.e., perennial ice, which survives throughout the year), which averaged a retreat of 10.2% and 11.4% per decade, respectively, for the period 1979–2007. This is consistent with ICESat measurements indicating decreased thickness in arctic ice and a decline in multi-year ice. For the period 2005–2008, multi-year ice decreased 42% in coverage and 40% in volume, a loss of ~6300 km3. While the Arctic Ice Coverage showed an accelerating downward trend, recent reports on the Arctic Ice Volume showed an even sharper decline then the Ice coverage. Since 1979, the ice volume has shrunk by 80% and in just the past decade the volume declined by 36% in the Autumn and 9% in the winter.

A 2010 study attributes that the recent Arctic temperature amplification was caused by the loss of sea ice itself, which exposes water instead of more reflective ice to solar radiation.