Photo via NASA Goddard/Flickr
The area covered by Arctic sea ice probably won't set a new record low this year. But according to new satellite measurements from the European Space Agency, the thickness of sea ice may still indeed reach record low levels in 2013.
The volume of sea ice, rather than its extent, is a more accurate measurement of the sort of climate changes taking place in the Arctic, the ESA says. Contrary to some truly poor, poor reporting in the Daily Mail over the weekend, Arctic ice area not hitting a new record low does not mean that the Earth is cooling.
Satellite measurements from the past three years show that at the end of last winter, the volume of Arctic sea ice was less than 15,000 cubic kilometers, lower than any other year. That indicates that regrowth of ice last winter was lower than usual. We'll only be able to determine whether a new record low volume will be set once satellite measurements are in from October, after sea ice melt halts for the year.
Regardless, the numbers show a massive decline. Thirty years ago Arctic sea ice volume at the end of winter was roughly 30,000 cubic kilometers. Using the ESA's recent data, the video below shows the variations in Arctic sea ice thickness dating from 2010 through April of this year.
Even before the ESA's satellite measurements started, data from NASA showed dramatic thinning of sea ice. Looking at the years from 2004 to 2007, NASA's satellite measurements showed an average thinning of Arctic ice of about seven inches per year. The area of multi-year sea ice—that is, ice that hasn't melted entirely in summer and then regrown in winter—declined 42 percent during that same time period. On average, multi-year sea ice is about 2.75 meters thick, with seasonal ice cover reaching 1.8 meters.
The declines seem stark, but the ESA has been careful to highlight that calculating the total magnitude of decline relies on a good understanding of how ice cover varies from year to year. BBC News quotes ESA's Professor Alan O'Neill as saying that while the current data is certainly consistent with what we can expect with global warming, "we also need to understand better the natural variation that occurs in the system on perhaps decadal timescales."
In other words, it's the same story as with climate change more broadly: There's long term climate change, brought about by increases in greenhouse gases from human industrial activity, mixed with other air pollution, some of which amplifies warming (black carbon) and some of which decreases warming (sulfates from coal burning, for example). That man-made climate change mixes with even longer-running natural cycles, some of which also amplify observed changes and some of which decrease them. The end result is that climate data can be relatively noisy, which makes relying on long-term trends important.