Computer simulations of the US National Center for Atmospheric Research indicate that the natural Arctic climate variability, like seasonal and annual variations in pressure systems, wind patterns and precipitation or cloud cover, could be larger than previously thought.

There are two sides to this news story, one up and one down. Let’s first focus on the chances of good news. The graph above shows [in red: 2006-2061] the possibility of divergence from the melting track for a period of up to a decade – and also a realistic chance of ice growth years.

When the NCAR climate researchers however zoom their model to a twenty year timescale the chances for ice growth have all but disappeared. Comparing the two graphs gives a nice impression of the difference between variability and trend:

There have been other reports lately that confirm the suggestion the Arctic variation may be larger than previously thought – although this may also imply the sensitivity to warming could in fact be greater, as so much ice seems to have disappeared during the Holocene Thermal Maximum, a Science publication just a week ago showed.

And in December last year Nature had a climate model study suggesting Arctic melting may progress in a more linear fashion than recent melting records have suggested.

The NCAR findings were published on Thursday in Geophysical Research Letters.

Arctic melting record 2011

Meanwhile, according to NSIDC, the Arctic sea ice in May, June and July reached its smallest extent ever. In August the ice melting slowed down to just below record year 2007. That year was not just hot, climatologists say, in the Arctic it was also windy. The one fits the trend of climate change, the other the definition of natural variability. The simple fact that the ice has not recovered from an extreme helps to understand where the trend is going.

© Rolf Schuttenhelm | www.bitsofscience.org