Arctic sea ice cover heading towards another record low?
The September 2007 sea ice minimum was probably the lowest extent of sea ice aerial extent in the Arctic in 50 years, definitely since satellite observations began in 1979. Last week the sea ice cover fell below the recorded extent at the same time in 2007.
Over the two upcoming weeks, shrinking sea ice will thus be one of the hottest science topics. The IPY Oslo Science Conference, scheduled for next week (8-12 June), will be the largest polar science gathering ever with more than 2000 participants. The conference will publish early results from the International Polar Year 2007-2008 (IPY), with particular emphasis on new knowledge about the linkages between climate change in the Polar Regions and global climate systems. This week (31 May - 4 June) a smaller international symposium on sea ice is schedule to meet in Tromsoe.
- What I find interesting about this year is that the Sea Ice extent in 2010 almost reached the end of March winter maximum but then dropped much more rapidly than previous years until it is now below the 2007 sea ice extent, says David Barber. - This increase, close to the maximum extent, and then rapid decrease is most likely due to the fact that the thickness of the ice continued to decline (2007-2010) even though the maximum extent almost reached winter norms.
Leading one of the world's largest International Polar Year (IPY) projects, Dr. David Barber has had a team of 200 international researchers examining how global warming in the Arctic predicts the effects of climate change on our planet. In November last year he returned from an expedition which largely failed to find multiyear ice in the Beaufort Sea off the Canadian coast. His ice breaker found hundreds of miles of what he called "rotten ice" - 50-cm thin layers of fresh ice covering small chunks of older ice.
- Our experience with this type of ice shows that by the end of summer, satellites may tell us that we have significant ice extent but it is so heavily decayed that it presents no barrier to ice navigation, at least in the Southern Beaufort Sea. The feedbacks that operate through the annual cycle are very strong and they continue to decrease the percent cover of multiyear sea ice to a point where the loss of all the thick multiyear sea ice could be imminent, says Dr. Barber
The maximum ice cover was reached almost a month later than normal this year. The melt season started on 31 March. The prior freeze season followed the curve recorded in the 2006-2007 season up until last part of February.
- Cold weather in March caused a late-season spurt in ice growth, confirms director of the National Snow and ice Data Center, Mark Serrreze. - This late season growth, however, consisted of thin ice, which was widely expected to quickly melt out with the onset of spring. While this is exactly what happened, the spring retreat has been especially rapid; as of May 25, extent had fallen to second lowest on record, just above what was observed in 2006.
Dr. Serreze says satellite data from NASA point to a weak and thin ice pack, with numerous openings (polynyas) in coastal seas. Based on the University of Colorado, Boulder, he studies Arctic climate, and the causes and global implications of climate change in the Arctic. Dr Serreze is well known for his research on the declining sea ice cover in the Arctic Ocean.
David Barber, director of the Centre for Earth Observation Science (CEOS) at the University of Manitoba, Winnipeg, wants to emphasise that the aerial extent of sea ice is only one of two major characteristics of sea ice and how it responds to global temperature, moisture and momentum; the second is sea ice thickness. The aerial extent, as measured by passive microwave radiometers, provides a consistent dataset which allows scientists to measure the extent of sea ice as a function of date and location in the Arctic. - Unfortunately we do not yet have a reliable way to measure ice thickness (although we are working on it with satellites like Cryosat-2), says Dr. Barber.
- The Pacific sector of the Arctic has lost a lot of summer ice over the last 30 years due to the circulation of the Beaufort Sea Gyre, the Transpolar Drift stream and a strong feedback to ice melt from the ocean surface mixed layer due to increase open water extent in the summer.
In September 2007, the last recorded minimum, the Arctic sea ice extent was only 4.13 million square kilometres. Much of the discussion covers the period since 1979, when consistent and reliable satellite observations began. However, considerable data exist for earlier years. One good source has been compiled by the United Kingdom's Hadley Centre for Climate Prediction and Research. Their analysis, based primarily on ship reports and aircraft reconnaissance, takes the record back to the turn of the 20th century.
Although the data quality prior to the early 1950s is debatable, no year in this century-long record comes close to matching what was observed and recorded in 2007. This record also points to a significant persistent downward trend in summer sea ice extent over at least the past fifty years. September 2007 sea ice extent was nearly 50% lower than during the 1950s and 1960s.
Last updated: 30.05.2010