Plunging Sea Ice could Amp Greenland Melt
June 17, 2016
Where we are now. If there is a big melt season this year, I’ll be live blogging it between June 29 and July 15.
NASA reports that some parts of Greenland were 36°F (20°C) warmer than “normal” — and remember, in this map, the new “normal” is the 2001–2010 average, which means it already includes a century of human-caused warming.
As we reported in mid-April, rainfall plus scorching temperatures over the country jump-started the summer melt season weeks early. On April 11, a remarkable 12 percent of Greenland’s massive ice sheet was melting — “smashing by a month the previous records of more than 10 percent of the ice sheet melting,” according to the Danish Meteorological Institute (DMI).
The record temperatures in June also led to an unusually high ice melt — covering nearly 40 percent of the ice sheet:
This graph shows the spikes in Greenland melting observed this spring. As glaicologist Jason Box recently told me, the weather in Greenland tends to come in waves of 10 days or so – and the spikes indicate warm spells that are extreme. A major controlling factor of this year’s peak melt will be whether or not a warm air mass settles over the ice sheet during the warmest weeks of summer.
Last summer the northern parts of the Greenland Ice Sheet experienced record melting as summer temperatures rose as high as 19°C (66°F), while southern Greenland was unusually cold, with just average melting. Now, scientists have linked the melt pattern with a 500-kilometer-wide, high-pressure vortex, known as a block, that loitered north of the island during June and July 2015, wreaking weather havoc. Such atmospheric blocks are expected to result from melting sea ice, some researchers say—a claim that has added fuel to a contentious dispute over the global influence of the warming Arctic.
Until now, the dispute has focused on how disappearing sea ice might be favoring extreme midlatitude weather, such as floods in Texas or heat waves in Russia. The new study is one of three recent papers that have expanded the debate to the melting of Greenland.
This video from 2013 is a crucial explainer of the ice-jet stream hypotheses, which is not going away, and has been strengthened by several recent publications.
Following record-high temperatures and melting records that affected northwest Greenland in summer 2015, a new study provides the first evidence linking melting in Greenland to the anticipated effects of a phenomenon known as Arctic amplification.
Arctic amplification, in the simplest terms, is the faster warming of the Arctic compared to the rest of the Northern Hemisphere as sea ice disappears. It is fueled by a feedback loop: rising global temperatures are melting Arctic sea ice, leaving dark open water that absorbs more solar radiation, and that warms the Arctic even more. Arctic amplification is well documented, but its effects on the atmosphere are more widely debated. One hypothesis suggests that the shrinking temperature difference between the Arctic and the mid-latitudes will lead to a slowing of the jet stream, which circles the northern latitudes and normally keeps frigid polar air sharply separated from warmer air in the south. Slower winds could create wilder swings of the jet stream, allowing warm, moist air to penetrate farther north.
The new study, published this week in Nature Communications, shows that those anticipated effects occurred over northern Greenland during the summer of 2015, including a northern swing of the jet stream that reached latitudes never before recorded in Greenland at that time of year.
“How much and where Greenland melts can change depending on how things change elsewhere on earth,” said lead author Marco Tedesco, a research professor at Columbia University’s Lamont-Doherty Earth Observatory and adjunct scientist at NASA Goddard Institute for Space Studies. “If loss of sea ice is driving changes in the jet stream, the jet stream is changing Greenland, and this, in turn, has an impact on the Arctic system as well as the climate. It’s a system, it is strongly interconnected and we have to approach it as such.”