North pole unlikely to be ice-free this summer, say UK scientists, but long-term decline continues
By Megan Darby
Arctic sea ice extent has shrunk 40% since the 1970s, prompting speculation as to when it might disappear altogether.
At a scientific gathering last September, Cambridge University’s Peter Wadhams said it could be as soon as summer 2015.
That’s unlikely, according to UK scientists, after the latest data showed sea ice volume had rebounded from low points in 2010 and 2012.
A study published in Nature Geoscience on Monday found an unusually cool summer in 2013 drove a 41% increase in sea ice volume that year.
Models show Arctic sea ice melting over the long term, UCL scientist and lead author Rachel Tilling said. The latest data shows “it can recover by a significant amount if the melting season is cut short”.
It means the Arctic might be more resilient than previously thought, added Andy Shepherd, professor at UCL and at the University of Leeds.
“Understanding what controls the amount of Arctic sea ice takes us one step closer to making reliable predictions of how long it will last, which is important because it is a key component of Earth’s climate system.
“Although the jump in volume means that the region is unlikely to be ice free this summer, we still expect temperatures to rise in the future, and so the events of 2013 will have simply wound the clock back a few years on the long-term pattern of decline.”
The melting icecap has seen the region opened up to shipping and oil exploration in the summer.
Back in early July, unusual warmth helped trigger a sudden and dramatic spike in melting at the surface of Greenland’s ice sheet. Exactly what was happening, and whether the trend would continue, was unclear.
Two weeks later, we now know that while the extent of surface melting is still significantly above average, it has not come close to breaking the record (at least not yet).
At the same time, another significant milestone has been reached: The amount of sunlight reflected by snow on the ice sheet’s surface plummeted during the first week of July to the lowest levels seen in the 16 years that it has been measured by satellite.
Reflectivity of snow is not as esoteric as it may seem. It’s actually an important climate variable — one that played a critical role in Greenland’s record-setting surface melt in July of 2012. At that time, just a little less than 100 percent of the surface experienced melting.
It was an astonishing event, and warm temperatures were partly to blame. But so was another factor: darkening of the snow by soot from wildfires burning many hundreds of miles away. And as you’ll see in a minute, soot may have been a factor this summer too.
When snow at the surface melts, and even when it warms just shy of the melting point, it will become darker. This causes its reflectivity, or “albedo,” to drop. Although this summer started out cold and snowy in Greenland, by the second half of June, “temperatures were everywhere markedly higher than average,” according to National Snow and Ice Data Center.
Those warm temperatures, as well as bright, sunny skies, were linked to a dome of unusually high atmospheric pressure that formed over Greenland in June. This was in keeping with a trend in recent decades of higher pressures over Greenland and part of the Central Arctic Ocean during summer.
The surface of an ice sheet can also become darker when winds carry soot in from distant wildfires. And, in fact, by early July smoke traveling west from wildfires in Alaska, and drifting east from conflagrations in Canada, converged over Greenland.
We’ll have to wait until data from surface surveys are available to know how much of an impact wildfire soot may have had on the surface of the Greenland Ice Sheet in early July.
We do know that during 2012’s record melting, it turned out to be a key factor.
That year, temperatures at the surface were unusually warm, and those balmy conditions were enhanced by a low layer of clouds consisting of tiny water droplets. The cloud layer was thin enough to allow sunlight to pass through and help melt the surface. At the same time it was also thick enough to trap a significant amount of thermal energy being radiated upward from the surface.
But a study published last year suggests those factors alone probably weren’t enough to cause surface melting in the high, dry central region of the ice sheet. Yet melting happened there too — because soot from distant wildfires had lowered the albedo of the snow below a critical threshold, the researchers found.
And that’s why albedo — however esoteric the concept may seem — is really important.
In fact, global warming, wildfires, albedo, and melting snow and ice, are all potentially tied together in a reinforcing feedback loop. Here’s how:
Warmer temperatures due to human activities have been contributing to increased wildfire activity. This has caused darkening of the snow in Greenland, which — as we’ve seen — has helped lead to increased melting at the ice sheet’s surface. More melting of the ice sheet’s surface decreases its albedo, which causes still more melting. Now, add in more global warming from human activities, and you’ve got more fires, lower albedo, more melting, lower albedo, etc., etc.
In 2012, the biggest spike in surface melting in Greenland occurred about mid way through the warm season. That’s where we’re at right now. I wouldn’t bet on a similar event happening this year, because it would take an extraordinary confluence of events.
Extraordinary, but not impossible.