New melt record for Greenland ice sheet

CCNY’s Marco Tedesco says ‘exceptional’ season stretched up to 50 days longer than average

 New melt record for Greenland ice sheet

Supraglacial lakes view from a helicopter. These lakes form from meltwater that collects in areas of the ice sheet, mainly as a consequence of surface topography. - ref. M. Tedesco/WWF

New research shows that 2010 set new records for the melting of the Greenland Ice Sheet, expected to be a major contributor to projected sea level rises in coming decades.

“This past melt season was exceptional, with melting in some areas stretching up to 50 days longer than average,” said Dr. Marco Tedesco, director of the Cryospheric Processes Laboratory at The City College of New York (CCNY – CUNY), who is leading a project studying variables that affect ice sheet melting.

“Melting in 2010 started exceptionally early at the end of April and ended quite late in mid- September.”

The study, with different aspects sponsored by World Wildlife Fund (WWF), the National Science Foundation and NASA, examined surface temperature anomalies over the Greenland ice sheet surface, as well as estimates of surface melting from satellite data, ground observations and models.

In an article published today in “Environmental Research Letters,” Professor Tedesco and co-authors note that in 2010, summer temperatures up to 3C above the average were combined with reduced snowfall.

The capital of Greenland, Nuuk, had the warmest spring and summer since records began in 1873.

Bare ice was exposed earlier than the average and longer than previous years, contributing to the extreme record.

“Bare ice is much darker than snow and absorbs more solar radiation,” said Professor Tedesco. “Other ice melting feedback loops that we are examining include the impact of lakes on the glacial surface, of dust and soot deposited over the ice sheet and how surface meltwater affects the flow of the ice toward the ocean.”

WWF climate specialist Dr. Martin Sommerkorn said “Sea level rise is expected to top 1 metre by 2100, largely due to melting from ice sheets. And it will not stop there – the longer we take to limit greenhouse gas production, the more melting and water level rise will continue.”

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 New melt record for Greenland ice sheet

Here’s a detail showing the crack propagating on the ice and meeting the streamflow, where it gets larger and accomodates the meltwater from the lake. - ref. M. Tedesco/WWF

 

 
In summer 2010, early melt onset in spring was triggered by above-normal near-surface air temperatures. This contributed to accelerated snowpack metamorphism (snow melts faster and in turns it gets ‘older’ sooner, with large grain sizes responsible for more solar radiation absorbed) and premature bare ice exposure, rapidly reducing the surface albedo. This implies that more solar energy is absorbed and hence more melting is occurring.  Warm conditions persisted through summer, with the positive albedo feedback mechanism being a major contributor to large negative surface mass balance anomalies (e.g., more melting than what was accumulated during the previous year). Summer snowfall was below average. This helped to maintain low albedo through the 2010 melting season, which also lasted longer than usual, until around mid September.

 

 

 

record melt for Greenland ice sheet

 
The figure on the left shows the anomaly map of melting days for 2010 derived from passive microwave data. Red areas indicate where melting lasted longer than average (up to 50 days).

 

 

 

 

 New melt record for Greenland ice sheet

The figure above shows the standardized melting index anomaly for the period 1979 – 2010. In simple words, each bar tells us by how many standard deviations melting in a particular year was above the average. For example, a value of ~ 2 for 2010 means that melting was above the average by two times the ‘variability’ of the melting signal along the period of observation. Previous record was set in 2007 and a new one was set in 2010. Negative values mean that melting was below the average. Note that highest anomaly values (high melting) occurred over the last 12 years, with the 8 highest values within the period 1998 – 2010. The increasing melting trend over Greenland can be observed from the figure. Over the past 30 years, the area subject to melting in Greenland has been increasing at a rate of ~ 17,000 Km2/year.

This is equivalent to adding a melt-region the size of Washington State every ten years. Or, in alternative, this means that an area of the size of France melted in 2010 which was not melting in 1979.

 

 

Here’s a short movie of videos and stills from Greenland that collected during 2009 and 2010 expeditions. You will see canyons through which water flows, supraglacial lakes and ice cracks routing surface water to the bottom of the ice sheet. The vocal background at the beginning is a Shaman Inuit Chant.

 

Related Story

 

melting ice sheet and snow

The decreases in Earth’s snow and ice cover over the past 30 years have exacerbated global warming more than models predict they should have, on average,

Shrinking snow and ice cover intensify global warming

 

Dr. Tedesco’s continuing research on ice sheets can be followed on www.cryocity.org.
For more on Arctic climate change, visit http://www.panda.org/arctic.

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    2 comments for “New melt record for Greenland ice sheet

    1. October 11, 2014 at 1:06 am

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    2. October 19, 2014 at 5:21 am

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