Pump up the volume (before the ice is gone)

By Gareth Renowden 12/08/2012


Early results from the European Space Agency’s Cryosat-2 satellite, launched in 2010, suggest that the Arctic sea ice volume in summer is currently being lost at the rate of 900 cubic kilometres per year, Robin McKie reports in The Guardian. By combining Cryosat data with other sources they have concluded that there has been a dramatic reduction in sea ice volume over the last eight years:

In winter 2004, the volume of sea ice in the central Arctic was approximately 17,000 cubic kilometres. This winter it was 14,000, according to CryoSat.

However, the summer figures provide the real shock. In 2004 there was about 13,000 cubic kilometres of sea ice in the Arctic. In 2012, there is 7,000 cubic kilometres, almost half the figure eight years ago. If the current annual loss of around 900 cubic kilometres continues, summer ice coverage could disappear in about a decade in the Arctic.

Ten years (or less) ’til its gone in summer. I hate to say I told you so, but…

Until Cryosat data came along, the only comprehensive source of information on sea ice volume was the PIOMAS modelling done at the University of Washington. The last time I looked at PIOMAS numbers, back in 2010, they showed an annual reduction of 780 km3 in the mean volume of sea ice at minimum in September. I’m not sure how the Cryosat and PIOMAS numbers will stack up against each other, but the Guardian report suggests that they are telling the same story. And that’s not a good thing, as McKie points out:

The consequences of losing the Arctic’s ice coverage, even for only part of the year, could be profound. Without the cap’s white brilliance to reflect sunlight back into space, the region will heat up even more than at present. As a result, ocean temperatures will rise and methane deposits on the ocean floor could melt, evaporate and bubble into the atmosphere. Scientists have recently reported evidence that methane plumes are now appearing in many areas. Methane is a particularly powerful greenhouse gas and rising levels of it in the atmosphere are only likely to accelerate global warming. And with the disappearance of sea ice around the shores of Greenland, its glaciers could melt faster and raise sea levels even more rapidly than at present.

This summer in Greenland has already been extraordinary, but ice melt is likely to go further into overdrive if the entire ice sheet is surrounded by rapidly warming oceans. I suspect that a lot of assumptions about what sorts of melt rates are feasible are going to have to be reviewed — and in the wrong direction.

Professor Chris Rapley of UCL said: “With the temperature gradient between the Arctic and equator dropping, as is happening now, it is also possible that the jet stream in the upper atmosphere could become more unstable. That could mean increasing volatility in weather in lower latitudes, similar to that experienced this year.”

Rapley’s point is key. The continuing loss of sea ice cover on the Arctic Ocean is already affecting northern hemisphere weather patterns1. The loss of sea ice is therefore driving changes in climate throughout the northern mid-latitudes. Climate change is no longer an abstract concept for future generations to worry about. It’s real, it’s here and it’s happening now.

[See also: Arctic Sea Ice blog, and for what might happen to winter ice, my thoughts from 2010.]

[MARRS]

  1. See Jennifer Francis’ presentation, linked a week ago.