Arctic Sea-Ice Recovery

New research suggests that the decrease in sea-ice seen in recent years in the Arctic may not be as bad as some have suggested. Summer Arctic sea-ice has been decreasing in extent for the past three decades, estimated at about 11 per cent a decade, although there are large interannual and regional variations.In September 2007 the ice extent declined to a record minimum coverage of 4.28 million square km. 2008 was only slightly larger. However, in 2009 there was a recovery restoring the ice extent to its extrapolated place on the decadal liner trend.In some climate models Arctic sea-ice thinning and retreat are predicted, driven by an ice-albedo feedback. Some models suggest that Arctic ice is in long-term decline leading to sea-ice free summers. Whilst such speculations have been amplified by the media there are many climate scientists who regard this as unlikely pointing to the little understood but dominant role that weather and large-scale atmospheric circulation plays.A limiting factor in predicting what might happen to Arctic sea-ice over the next decade is our poor knowledge of variations in ice thickness over the region.To gather new data on ice thickness researchers led by Dr Christian Hass of the University of Alberta, undertook a series of aircraft flights last year during which a sensor was towed beneath the aircraft whilst flying an Arctic transept. It was the first time that a fixed-wing aircraft had carried out a survey over regions of old ice in the important region between Svalbard and Alaska.Accurate ice thickness data is sparse over wide regions of the Arctic although the situation has improved a little recently due to airborne and satellite laser altimetry which can give the height of the ice above the water level. This data, combined with assumptions about ice density profiles, snow density and depth can give some information about ice thickness although it must be said that the errors are large and this approach is in its early stages.The researchers involved in the new study used another technique, Electromagnetic Induction, which detects the distance between the sensor and the ice-water boundary. The sensor, lowered 10 metres below an aircraft and towed 20 metres above the ice, was flown over key Arctic regions north of Svalbard, Greenland, Canada and Alaska. It is not a very accurate technique (precision of about 10 cm) but it is useful to study relative changes.Nine flights were undertaken with a total length of 2412 km. The thickest ice (up to 6.06 m) was found along the coast of Ellesmere Island. The thinnest was in the Beaufort and Chukchi seas and the Fram Strait (1.69 – 1.88 m). Click on image to enlarge. Overall the researchers conclude that the distribution of old Arctic ice has changed little since 2007 and what changes there have been are well within the range of natural variability. They speculate that the large ice loss seen in 2007 may have been offset by weather patterns since then that prevented further ice loss.“There is still hope for the ice,” said Christian Hass, adding that in many ways thje ice is in better shape entering the melt season than it has been for years. He dismisses suggestions that a “tipping point” may soon be encountered that will result in catastrophic, runaway ice loss. Extreme melts there may be, but he considered they would be compensated for by rapid recoveries.This technique is set for a busy future. It is scheduled to be used extensively during the forthcoming test runs with the Cryosat satellite as it observes sea-ice between Canada and the North Pole between 2011-12.Feedback: david.whitehouse@netzerowatch.com