“Other people had argued that 75 to 80 percent ice volume loss was too aggressive. What this new paper shows is that our ice loss estimates may have been too conservative, and that the recent decline is possibly more rapid.”
—polar scientist Axel Schweiger
By now most people are well aware of the shrinking ice cap at the North Pole. Side-by-side comparisons of satellite photos of the Arctic show that in the last thirty years the size of the ice cap has shrunk dramatically.
What a lot of people forget is that those side-by-side photos only tell part of the story. They are limited to showing the shrinking area covered by the ice cap. But there’s a third dimension to that floating ice cube up north, and the thickness or volume has been declining too. But by how much?
A new report just published online in Geophysical Research Letters reveals that the Arctic sea ice volume is now only 20 percent of what it was back in 1979, 3261 cubic kilometres down from 16,855 cubic kilometres. It turns out the volume is decreasing at a much quicker rate than the area: in other words, it’s getting thinner more quickly than it’s shrinking in extent.
A number of satellites have been measuring the amount of ice lost at the North Pole for years, but the recent report obtained more useful information from CryoSat-2, a satellite operated by the European Space Agency and better able to measure volume rather than just area.
A press release from the Natural Environment Research Council explains how it manages to measure volume. For those of you interested in understanding the technology involved:
CryoSat-2 measures ice volume using a high-resolution synthetic aperture radar altimeter, which fires pulses of microwave energy down towards the ice. The energy bounces off both the top of sections of ice and the water in the cracks in between. The difference in height between these two surfaces let scientists calculate the volume of the ice cover.
Loss of Arctic sea ice is significant because it can contribute to positive feedback mechanisms that can accelerate global warming even further. For one, the darker ocean absorbs more solar energy than the more reflective ice does, decreasing the planet’s albedo. Another is that the subsequent warmer ocean waters will contribute to the melting of permafrost, leading to the release of methane that’s been stored inside that permafrost, and in the ocean’s deep methane hydrate stores.
Losing sea ice volume is sometimes difficult to appreciate because we’re more used to looking at Earth’s surface, not thinking about that surface in the third dimension. Here’s a brief video that shows in graphic format what’s been happening these last three decades.
Once more it seems that it’s become even more imperative that we cut back our emissions and strive to steer clear from business-as-usual. So many times it seems that as we probe deeper into the state of things, we find it’s worse than we used to think more often than we find it’s not as bad as we used to think.