Danish scientists monitoring Greenland’s ice sheet didn’t believe what they saw, Monday. The model showed that over 10 percent of Greenland’s surface had melted a millimeter or more on the 11th of April, two months early. April 11 was a month earlier than earliest melt event on record in May, 2010. The Danish scientists were “incredulous.” They started looking at the weather data to try to get a handle on what was wrong with the model. They were shocked. Warm rain had fallen at elevations of over 5000 feet on the ice sheet. Above freezing temperatures at those elevations are a heat wave in July. Warm rain in April on Greenland at elevations above 5000 feet was something no one had ever seen before.
Based on observation-initialized weather model runs by DMI, almost 12% of the Greenland ice sheet had more than 1mm of melt on Monday 11th April, following an early start to melting the previous day. Scientists at DMI were at first incredulous due to the early date. “We had to check that our models were still working properly” said Peter Langen, a climate scientist at DMI. “Fortunately we could see from the PROMICE.dk stations on the ice sheet that it had been well above melting, even above 10 °C. This helped to explain the results”. The former top 3 earliest dates for a melt area larger than 10% were previously all in May (5th May 2010, 8th May 1990, 8th May 2006).
“Even weather stations quite high up on the ice sheet observed very high temperatures on Monday”, said Robert Fausto, a scientist at GEUS who maintains PROMICE.dk melt data. “At KAN_U for example, a site at 1840 m above sea level, we observed a maximum temperature of 3.1°C. This would be a warm day in July, never mind April”. Other PROMICE stations in the network at lower levels had daily average temperatures between 5 and 10 °C.
Similarly, around the coast of Greenland where DMI has climate records dating back to 1873, Greenland came close to setting a record temperature for the whole of Greenland in April. Kangerlussuaq measured a daily maximum of 17.8°C and the DMI observation station at the Summit of Greenland set a new “warm” April record of -6.6°C. “Averything is melting” observed Nuuk resident Aqqaluk Petersen.
This unprecedented melting is not an isolated event. Since the first of January when the polar vortex in the troposphere (the layer of the atmosphere where our weather takes place) broke down warm air has flooded the Arctic. Warm water pushed up the coast of Norway into the Barents sea of the Arctic releasing heat that drove temperatures to as much as 50 degrees F above normal over waters that used to be ice covered. Through the winter the Arctic sea ice extent grew feebly to record monthly lows in January and February. As the sun began to return to the Arctic in March, warming came faster than normal because snow extent was below normal. The record warm winter is leading to a very warm spring. The record first Greenland melt is part of a pattern of unprecedented Arctic warmth.
There’s reason to fear that this is the start of an Arctic meltdown where sea ice will collapse to record low volume and extent while Greenland melts. We know from climate records that spring warmth is amplified by the darkening it brings to the Arctic. The last ice age ended when the earth’s wobble aligned to bring maximum heating to the Arctic in late spring. As spring warmth melts ice the dark ground and dark water soaks up the solar energy and by midsummer the enhanced melting multiplies the heat. That’s what’s happening right now. A feedback loop is starting that will bring extreme melting to the Arctic this summer if something doesn’t stop it.
This melting is already affecting Greenland’s ice by bringing warm water into cracks and crevasses. The warmth added now will penetrate into the ice cap setting the stage for more summer melting. The warm rains, by melting the bright snow cover, will darken the surface enhancing the uptake of solar heat. Surface darkening speeds up melting.
The extreme warmth in Greenland and over the Arctic ocean is all linked to the flux of warm water that built up off the east coast of North America into the polar seas and the Arctic ocean.
When warm water builds up of the east coast, research has found that it takes several years to affect the Arctic. Some Danish scientists though that the flow of warm water was slowing down and that the Arctic would cool but ocean temperature data and gravity data show a resurgence of warm salty water moving around the cold subpolar gyre south of Greenland. Very low sea surface heights over the gyre indicate that the water is very dense now and deep water formation is resurgent.
The warm Atlantic water that is entering the Arctic is weakening the polar vortex, increasing the intensity of south to north and back waves in the jet stream. One of these extreme south to north waves broke over Greenland forming a “blocking high” causing the unprecedented April melt event.
This is the beginning of a summer to remember.
Polar portal has the full write up on the details of this early melting event: polarportal.dk/...