- Changes in Minimum Arctic Sea Ice Extent - NASA
The Arctic region is undergoing dramatic changes to its sea ice cover in terms of both thickness and extent. As detailed in an article written by researchers at the National Snow and Ice Data Center (NSIDC), virtually all climate models used by the Intergovermental Panel on Climate Change (IPCC) predicted a decline in Arctic sea ice extent over the 21st century but recent research has found that the Arctic sea ice cover is decreasing more rapidly than predicted.
The Arctic Sea Ice Cover
Sea ice is frozen seawater that forms in high latitude oceans during winter. By late winter, sea ice covers roughly 14-16 million square kilometres in the Arctic. Most of this ice melts during summer although approximately 7 million square kilometres remains at the beginning of the following winter. Some sea ice can persist for two or more years (termed “multiyear ice”).
Why Is Sea Ice Important?
Sea ice is important for regulating climate. Its light colour means it reflects more of the sun’s radiation than dark ocean water, and therefore reduces heat absorbed by the planet. A decrease in sea ice leads to increased absorption of solar radiation, which causes warming and an increase in ice melt. This feedback cycle is one of the reasons changes in sea ice cover are so worrying.
Sea ice also affects heat exchange between the ocean and atmosphere and regulates precipitation in polar regions, which also influences climate. Moreover, the Arctic ecosystem is reliant on sea ice cover, with a number of animals (perhaps the most well known being the polar bear) being threatened by changes in sea ice conditions. There is already evidence that polar bear populations are being affected by decreasing sea ice cover.
The Evidence for Arctic Sea Ice Decline
In recent years a number of researchers have studied long-term changes in Arctic sea ice thickness and extent. The aim is to identify trends and use those patterns to work out what may happen in the future. One of the main challenges is figuring out what is a trend and what is normal variability but researchers have found compelling evidence for a decline in Arctic sea ice cover over several decades.
The NSIDC details worrying findings arising from recent studies. One research group found that Arctic sea ice extent decreased by approximately 8% per decade between 1953 and 2006, while another group showed that Arctic sea ice thickness had decreased by roughly 1.3m during the late 20th century. Other studies have made similar observations.
Shorter term patterns are also cause for concern. The September minimum sea ice extent in the Arctic was unusually low in 2002, 2005, 2007, 2008 and 2009 compared with records from 1979 to the present, with a record low in 2007, when sea ice extent was 39% less than the 1979-2000 average minimum value.
In recent years low summer sea ice cover has been accompanied by poor winter recovery, leading to a decrease in multiyear ice. First year ice is thin and more vulnerable to melt than multiyear ice, so the trend towards a thinner, younger ice cover suggests that the Arctic sea ice may be becoming increasingly vulnerable to temperature changes.
Why is the Arctic Sea Ice Declining?
It is difficult to determine the cause of trends in sea ice cover as it experiences a lot of natural variability. However, many experts think that an increase in global average temperature associated with an increase in atmospheric greenhouse gases is forcing the general trend towards thinner, less extensive sea ice cover. As sea ice cover decreases, feedback cycles such as that described above become increasingly important.
Climate models are used by organisations such as the IPCC to predict what is likely to happen to the Earth in years to come. These models use current climatic conditions and incorporate projected future input of greenhouse gases to the atmosphere, and they are used to determine likely future environmental conditions. Worryingly, sea ice observations indicate that the Arctic ice cover is declining more rapidly than IPCC models predicted.
Sources
NASA 2005, Arctic Sea Ice Continues to Decline, Arctic Temperatures Continue to Rise In 2005, written 28 September 2005, Nasa.gov Accessed July 2010
NASA 2006, Slow Retreat of Sea Ice Lengthens Arctic Polar Bear's Fast, written 13 September 2006, Nasa.gov Accessed July 2010
NSIDC, State of the Cryosphere, updated 18 February 2010, Nsidc.org Accessed July 2010
Margaret Wallace - Hello, my name is Mags Wallace. I did an MESci in geophysics and Geology from Liverpool University, followed by a PhD in Physical ...
