Arctic Melting In “Uncharted Territory”
May 18, 2016
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One of the oldest and best-established ideas about global warming is that it will hit the Arctic the hardest. The concept, which goes back to papers published decades ago, is called “Arctic amplification,” and the basic idea is that there’s a key feedback in this system that makes everything worse.
It works like this: Warmer air melts more of the sea ice cover that sits atop the Arctic ocean, especially during summer, which is, of course, ice melt season. That means the ocean is able to absorb more solar radiation than before, when it was covered with ice that reflected this sunlight away. That means there’s more heat retained in the system — and so on, and so on.
So Arctic amplification has long been understood — and, confirming the theory, the Arctic has already been warming much faster than the more temperate latitudes. Even in this context, though, scientists have been noting that there seems to be something especially stark about what’s happening atop the world this year, which has seen overall temperatures soar to new highs.
“We’re in record breaking territory no matter how you look at it,” says Jennifer Francis, an Arctic specialist at Rutgers University who has published widely on how Arctic changes affect weather in the mid-latitudes. “The ice is really low, the temperatures are really high, the fire seasons have started earlier,” she says.
April in Greenland is typically very cold, though some years buck the trend. In 2012, for example, the surface of the ice sheet started melting early and then experienced the most extensive melting since the start of the satellite record in 1978. Weather events and temperature anomalies this April suggest that 2016 may be off to a similar start.
The map above shows land surface temperatures for April 2016 compared to the 2001–2010 average for the same month. Red areas were hotter than the long-term average; some areas were as much as 20 degrees Celsius (36 degrees Fahrenheit) warmer. Blue areas were below average, and white pixels had normal temperatures. Gray pixels were areas without enough data, most likely due to excessive cloud cover.
This temperature anomaly map is based on data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Observed by satellites uniformly around the world, land surface temperatures (LSTs) are not the same as air temperatures. Instead, they reflect the heating of the surface by sunlight, and they can sometimes be significantly hotter or cooler than air temperatures.
“The most remarkable aspect here is the incredible departure from 2001-2010 average, especially deep in the ice sheet interior,” said Santiago de la Peña, a research scientist at Ohio State University. “This is accentuated by the fact that the northern regions of the United States and Canada actually experienced cooler than usual temperatures.”
According to de la Peña, a high-pressure weather system sat over the ice sheet through most of April. The system caused temperatures across Greenland to spike, reaching or matching record temperatures in many places. “There have been occasional warming events in the past during spring over Greenland,” he noted, “but they affected only local areas and were not as intense.”