In the Arctic, the area covered by sea ice that survives through the summer has been on a downward trend for as long as we've been monitoring it. But the area of ocean covered by ice only tells part of the story. Some of that ice is relatively thin, having only formed during the previous winter. Other areas have thick ice that has built up over several years and is more likely to survive through the summer.
Getting a grip on the ice thickness throughout the Arctic has been a challenge. While there have been some sporadic regional surveys, they don't provide a complete picture of the polar region. That changed with the launch of the ESA's CryoSat-2 satellite, which has been gathering data since 2010. Now, researchers have used the data to show that the thickness of the sea ice is quite dynamic, with a single cold summer being enough to reverse part of the downward trend.
CryoSat-2 has an instrument that can detect the altitude from the top of sea ice, even differentiating it from snow on the ice's surface. To understand ice thickness, the authors of the new paper compared that to the height of the ocean near the ice. From there, based on what we know about ice's buoyancy, it's possible to calculate the thickness. This is a little more complicated than it sounds, however, given that they had 88 million individual measurements spanning four years (2010-2014).
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