Chilly Manjaro | The Watchers

Rate of summer ice melt smashes two previous record lows and prompts warnings of accelerated climate change. Arctic sea ice cover likely melted to its minimum extent for the year on September 16, according to scientists at the National Snow and Ice Data Center (NSIDC).

Satellite images show that the rapid summer melt has reduced the area of frozen sea to 3.41 million square kilometers (1.32 million square miles), now the lowest summer minimum extent in the satellite record – less than half the area typically occupied four decades ago.

The Arctic Sunrise makes its way through the ice floes during Greenpeace’s expedition to document the lowest sea ice level on record. Sea ice in the Arctic has shrunk to its smallest extent ever recorded, smashing the previous record minimum and prompting warnings of accelerated climate change (Credit: Daniel Beltrá/Greenpeace)

A record low in 2007 of 4.17m sq km was broken on 27 August 2012; further melting has since amounted to more than 500,000 sq km.

Sea ice extent fell to 4.10 million square kilometers (1.58 million square miles) on August 26, breaking the lowest extent on record set on September 18, 2007 of 4.17 million square kilometers (1.61 million square miles). On September 4, it fell below 4.00 million square kilometers (1.54 million square miles), another first in the 33-year satellite record.

Arctic sea ice extent for September 16, 2012 was 3.41 million square kilometers (1.32 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole. (Credit: National Snow and Ice Data Center)

Arctic Ocean could be ice-free in summer months within 20 years, leading to possibly major climate impacts. Recent climate models suggest that ice-free conditions may happen before 2050, though the observed rate of decline remains faster than many of the models are able to capture. Arctic sea ice cover has been shrinking since the 1970s when it averaged around 8m sq km a year, but such a dramatic collapse in ice cover in one year is highly unusual.

Satellite data reveal how the new record low Arctic sea ice extent, from Sept. 16, 2012, compares to the average minimum extent over the past 30 years (in yellow). Sea ice extent maps are derived from data captured by the Scanning Multichannel Microwave Radiometer aboard NASA’s Nimbus-7 satellite and the Special Sensor Microwave Imager on multiple satellites from the Defense Meteorological Satellite Program. (Credit: NASA/Goddard Scientific Visualization Studio)

Sea ice experts said they were surprised by the collapse because weather conditions were not especially conducive to a major melt this year. The ice is now believed to be much thinner than it used to be and easier to melt.

Arctic sea ice follows an annual cycle of melting through the warm summer months and refreezing in the winter. The sea ice plays a critical role in regulating climate, acting as a giant mirror that reflects much of the Sun’s energy, helping to cool the Earth.

The graph above shows Arctic sea ice extent as of September 17, 2012, along with daily ice extent data for 2007 and 2005, the previous record low years. 2012 is shown in blue and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. (Credit: National Snow and Ice Data Center )

David Nussbaum, chief executive of WWF-UK, explains that the disappearance of Arctic ice is the most visible warning sign of the need to tackle climate change and ensure we have a world fit to pass on to the next generation. The sheer scale of ice loss is shocking and unprecedented. This alarm call from the Arctic needs to reverberate across Whitehall and boardrooms.

Canadian scientists said this week that the record melt this year could lead to a cold winter in the UK and Europe, as the heat in the Arctic water will be released into the atmosphere this autumn, potentially affecting the all-important jet stream. While the science is still developing in this area, the Met Office said in May that the reduction in Arctic sea ice was contributing in part to the colder, drier winters the UK has been experiencing in recent years.

The animation below, released by the NOAA on September 17, shows the 2012 time-series of ice extent using data from the DMSP SSMI/S satellite sensor:

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