The melting season is now fully under way in the high Arctic. Months of relatively warm temperatures and nearly continuous sunshine have taken their toll on the ice that blankets the Arctic Ocean. By mid-September, the sea ice will reach its low point for the year, before starting its annual re-freeze. All of this is normal, but the conditions scientists are seeing this year are anything but normal. “Right now,” said Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colo., in an interview, “we’re on a record pace for ice loss. If the melt stopped today, we’d have the fourth lowest ice coverage on record.”
CryoSat determines variations in the thickness of floating sea-ice so that seasonal and interannual variations can be detected.
Credit: ESA /AOES Medialab
According to Serreze and other ice experts, we may be on the verge of an all-time low for Arctic ice coverage. In fact, as of August 12, Arctic sea ice extent had fallen below the level for the date seen in the record melt year of 2007. A new report just out from the Study of Environmental Arctic Change, or SEARCH, forecasts that sea ice coverage should dwindle to just 4.3 million square kilometers by mid-September. If that turns out to be correct it would come very close to beating the all-time record of 4.28 million square kilometers, set in 2007 — and given the uncertainties in the forecast this far out, the 2007 record could easily fall.
That’s worrisome enough by itself: the less ice covering the Arctic Ocean, the more of the Sun’s energy the underlying seawater absorbs, which ultimately leads to even more melting, along with generally higher Arctic temperatures overall. But preliminary readings from the European CryoSat-2 show that the remaining ice is far thinner than normal, which means that an especially warm spell, either now or sometime in the next few years, could melt a huge area of ice very quickly.
It’s not entirely clear why this year’s meltback is proceeding so fast. On average, thanks to global warming, there’s been less ice each summer since 1979, when satellite observations of the North Polar Region began (before that, scientists had to rely on random observations by ships and planes). But the drop hasn’t been a steady one, thanks to weather patterns that might speed melting one year and hold it back the next. The all-time record minimum in ice cover came in September of 2007; since then, there’s been a very slight rebound.
That may now be at an end. This year’s plunge in sea ice may be in part due to a huge cyclonic storm — like a tropical storm, only much chillier — that struck the Arctic during the first week of August. “It’s one of the strongest I’ve seen in more than 20 years,” Serreze said. Such storms typically break up sea ice, allowing it to melt more quickly; they also churn up warmer, saltier water from beneath the surface, which accelerates the melting. Sure enough, Serreze said, “we saw very rapid ice loss.” But there’s no smoking gun, he said, that proves the storm was the primary reason for ice loss. “The place with the biggest loss was the East Siberian Sea, where the ice was already poised to go.”
Whether this year’s ice loss ends up being worse than the melting in 2007 isn’t the most important question. “What is worrying,” said CryoSat-2 mission scientist Mark Drinkwater in an email, “is the reductions in volume and mass of the sea ice.” The reason is simple: if you’re just looking at how much of the Arctic Ocean is covered by ice, a thin layer is just as good as a thick layer. But a thin layer can melt much more easily, whether buffeted by storms or not, and decades of summer melting have thinned the ice dramatically. “Perhaps most disturbing,” Drinkwater said, “is the fact that current models would appear to be significantly underestimating the true values.”
In short, the new data confirm what scientists have been seeing for several years now: the ice is thinning a lot faster than climate models originally predicted it would, and while no one knows for sure when the first truly ice-free summer in the Arctic Ocean will come, it could plausibly be within years, not decades. That would be terrible news for seals and polar bears, but it could also accelerate the warming of the entire planet.
Open water will warm the ocean itself, which could undermine the glaciers on nearby Greenland. The generally warmer conditions could also speed the melting of permafrost on land in Alaska, Canada and Russia. That could release extra heat-trapping carbon dioxide into the atmosphere, which would further turbo charge global warming. So could the release of methane as plant material decays in soggy marshes, or escapes from hydrate deposits on the sea floor.
As for this year’s melting, it’s always possible that the weather could change and the current rate of ice loss could slow. Even if that happens, however, Arctic summer sea ice seems to be heading, more or less inexorably, to record low territory. Eventually, climate scientists say, the Arctic Ocean is likely to be nearly ice-free during the summer, if current trends continue.