The blanket of sea ice that floats on the Arctic Ocean appears to have reached its lowest extent for the year. Arctic sea ice extent fell to 4.33 million square kilometers (1.67 million square miles) on September 9, 2011. This year’s minimum was the second lowest in the satellite record, which started in 1979. The lowest extent was recorded in 2007.
Over the last thirty years, ice extent, a two-dimensional measure of the ice cover on the Arctic Ocean, has declined in all months, with a more pronounced drop in summer. Scientists attribute this decline in large part to climate change. Arctic sea ice melts and refreezes in an annual cycle, reaching its lowest point in late summer, and its highest point in late winter.
Scientists are worried about declining Arctic sea ice because the ice plays an important role in global climate. The bright white sea ice reflects sunlight and heat back into space, so that the Arctic region remains cooler than it otherwise would. The cold temperatures in the Arctic in turn act as a sort of air conditioner for the rest of the world.
As ice cover retreats, additional areas of open water absorb more heat during the summer, leading to a positive feedback effect where the loss of sea ice in turn leads to more sea ice loss and puts more heat into the upper part of the ocean. While ice will grow back during the winter period of polar darkness, come spring it will be thinner than it used to be, melting out all the more easily the next summer.
The last five years (2007 to 2011) have been the five lowest extents in the continuous satellite record, which extends back to 1979. While the record low year of 2007 was marked by a combination of weather conditions that favored ice loss (including clearer skies, favorable wind patterns, and warm temperatures), this year has shown more typical weather patterns but continued warmth over the Arctic. This supports the idea that the Arctic sea ice cover is continuing to thin. Models and remote sensing data also indicate this is the case. A large area of low concentration ice in the East Siberian Sea, visible in NASA Moderate Resolution Imaging Spectroradiometer (MODIS) imagery, suggests that the ice cover this year is particularly thin and dispersed this year.
Please note that this number (i.e., 4.33 million square kilometers) is preliminary – changing winds could still push the ice extent lower. During the first week of October, NSIDC will issue a full analysis of the possible causes behind this year’s ice conditions, including a discussion of how the summer’s low ice extent may affect the winter ice growth season ahead, and graphics comparing this year to the long-term record.
The National Snow and Ice Data Center (NSIDC) is part of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder. NSIDC scientists provide Arctic Sea Ice News & Analysis content, with partial support from NASA.
Source: NSIDC.
