Arctic sea ice back to record low

Summer ice cover reaches fourth lowest value since records began

Size of sea ice on September 14, 2010 © Kaleschke / Universität Hamburg
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The summer sea ice cover of the Arctic will reach one of the lowest levels of the past 20 years this year. This is shown by evaluations of satellite images. For the fourth time in a row, the Arctic Ocean is covered with less ice than would have been expected after the downtrend of recent decades.

The last decade was the warmest since the beginning of the climate recordings, which has recently been confirmed by new analyzes of climate data. The hardest hit is the high north of our planet, where temperatures rise disproportionately high - with fatal consequences for the Arctic ice sheet. It keeps shrinking. After the record low of the summer ice rink in September 2007, there is no sign of a recovery this year, as climate researchers said in a press conference on Monday.

Fourth lowest since the beginning of the measurements

Satellite images show that the sea ice area around the North Pole at the end of the Arctic summer will average around 4.9 million square kilometers in September. On average over the past 40 years, the ice had covered an area of ​​6.7 million square kilometers in September; In 1980, the expansion was 7.8 million square kilometers. The expected average for this September is one of the four lowest values ​​since the beginning of the satellite evaluation in the early 1970s.

Negative trend continues unbroken

"The results are questionable because the negative development has accelerated. There is no question of a 'recovery' of the ice cover, "explains Lars Kaleschke, Professor at KlimaCampus, University of Hamburg. The lowest sea ice extent registered the scientists in 2007 with 4.2 million square kilometers. The sea ice minimum is subject to strong fluctuations from year to year; on a statistical average, the area has been reduced by about eight percent per decade since 1970. According to Professor Rüdiger Gerdes of the Alfred Wegener Institute for Polar and Marine Research, this development can not be explained solely by natural causes, but above all by man-made climate change.

IPCC forecasts already undercut

In the past two years, the sea ice area has again increased compared to 2007. Therefore, it was not excluded that this year, the negative trend of recent years could be broken. However, this expectation was not confirmed. That the actual ad

Ice conditions in the Arctic meanwhile fall below the calculated values ​​in the global climate models of the IPCC report, according to Gerdes can have different causes.

Gerdes is a sea ice expert of the Alfred Wegener Institute, where he is responsible, inter alia, for the evaluation of climate models for the Arctic.

Interplay of climate change and decadal oscillation

"Today, long-term natural climate variability and human influence play comparable roles in Artkis, " says Gerdes. The anthropogenic temperature rise coincides with a warm phase of the Atlantic Multidecadal Oscillation (AMO); both together lead to the extreme ice drop of the past years. In the AMO, a warm period followed for a cold period between 1860 and 1930 with lower water surface temperatures in the 1940s. Since the 1990s, another warm period followed. For the future development of sea ice, it is crucial how quickly the AMO returns to its cold phase.

According to Gerdes, the fact that the warm period in the 1940s did not lead to the melting of sea ice to the present extent is due to the different development of sea ice thickness. "In the meantime, the ice mass in winter had in some cases fallen below the critical point that permitted melting in the summer. 70 years ago, the winter ice was so thick that it could not happen, "said Gerdes.

(Alfred Wegener Institute, Climate House Bremerhaven, KlimaCampus, 14.09.2010 - NPO)