TORONTO, April 1, 2016 – A new study by researchers from Denmark and Canada's 91��ɫ, published in , has found that the climate models commonly used to simulate melting of the Greenland ice sheet tend to underestimate the impact of exceptionally warm weather episodes on the ice sheet.

The study investigated the causes of ice melt during two exceptional melt episodes in 2012, which occurred from July 8 to 11 and from July 27 to 28. During these exceptional melt episodes, which can be regarded as an analogue to future climate, unusually warm and moist air was transported onto the ice sheet. During one episode, the researchers measured the ice sheet melting at more than 28 cm per day, the largest daily melt rate ever documented on the ice sheet. While the two brief melt episodes only lasted six days combined, or six per cent of the melt season, they contributed to 14 per cent of the total melt.

Researchers service one of PROMICE’s automatic weather stations on the Greenland ice sheet that was used in the study. Photo by William Colgan, 91��ɫ

Using the Programme for Monitoring of the Greenland Ice Sheet () automatic weather station data, the researchers ranked the energy sources contributing to surface melt during 2012 at twelve PROMICE sites around the ice sheet periphery. While ice sheet melt is usually dominated by the radiant energy associated with sunlight, the researchers found that the energy associated with air temperature and moisture content, rather than radiant energy, was responsible for more melt during the 2012 exceptional melt episodes.

As Robert Fausto of the Geological Survey of Denmark and Greenland, lead author of the study, says, “When we were analysing our weather station data, we were quite surprised, that the exceptional melt rates we observed were primarily caused by warm and moist air, because ice sheet wide melt is usually dominated by radiant energy from sunlight. “

This finding has implications for how the scientific community projects future ice sheet melt using climate models. In the study, the researchers also show that while the models presently used to project ice sheet melt can accurately simulate melt due to radiant energy, models tend to systematically underestimate melt due to the non-radiant energy processes they document.

“Glaciological instrumentation capable of automatically recording the daily rate of melting in exceptional melt circumstances, where the ice surface lowers by close to 10 m in a few months, has only emerged in the last decade or so, thanks to PROMICE. The detail of PROMICE observations is permitting new insights on brief, but consequential, exceptional melt events," says of the Lassonde School of Engineering at 91��ɫ, a co-author of the study.

Fausto adds that, “Exceptional melt episodes dominated by non-radiant energy are expected to occur more frequently in the future due to climate change. This makes it critical to better understand the influence of these episodes on ice sheet health.”

*Photo available. Cutline: Researchers service one of PROMICE’s automatic weather stations on the Greenland ice sheet that was used in the study. Photo by William Colgan

��is known for championing new ways of thinking that drive teaching and research excellence. Our 52,000 students receive the education they need to create big ideas that make an impact on the world. Meaningful and sometimes unexpected careers result from cross-discipline programming, innovative course design and diverse experiential learning opportunities. 91��ɫ students and graduates push limits, achieve goals and find solutions to the world’s most pressing social challenges, empowered by a strong community that opens minds. 91��ɫ U is an internationally recognized research university – our 11 faculties and 24 research centres have partnerships with 200+ leading universities worldwide. As Canada’s only fully bilingual campus, Glendon is one of the faculties of 91��ɫ dedicated to excellence in bilingual postsecondary education.

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Media Contacts:
Sandra McLean, 91��ɫ Media Relations, 416-736-2100 ext. 22097 / sandramc@yorku.ca

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91��ɫ and University of Texas create map of past ice sheet movement

TORONTO, February 4, 2016 – Scientists have created the first map that shows how the Greenland Ice Sheet has flowed over time, revealing that ice in the interior is now moving more slowly toward the edges than it has, on average, over the past 9,000 years.

In comparing this paleo-velocity map to modern flow rates, researchers from 91��ɫ and The University of Texas, as well as other institutions, found the ice sheet’s interior to be moving slower now than it was during most of the Holocene, a geological period that began at the end of the last glacial period roughly 11,700 years ago and runs to the present.

The , which researchers said don’t change the fact that the ice sheet is now rapidly losing mass and contributing to sea level rise, will be published in the Feb. 5, 2016 issue of the journal . Along Greenland’s periphery, many glaciers are now rapidly thinning. However, the vast interior of Greenland, as it moves more slowly, has been gradually thickening over millennia. This new study documents and describes why this is happening.

“We found three reasons for this gradual slowing and thickening of the ice sheet in the Greenland’s interior,” said����of 91��ɫ’s Lassonde School of Engineering, second author of the study. The first two are an increase in snowfall over the last 9,000 years and a gradual stiffening of the ice sheet. “The ice that formed from snow that fell in Greenland during the last ice age is about three times softer than the ice being formed today.”

This is causing the ice sheet to slowly become stiffer and as a consequence flow slower and get thicker over time. This is especially the case in southern Greenland, where higher snowfall rates have led to rapid replacement of ice from the last glacial period with more modern Holocene ice.

“But that didn’t explain what was happening elsewhere in Greenland, particularly the northwest, where there isn’t as much snowfall,” said lead author Joe MacGregor of The University of Texas at Austin’s Institute for Geophysics (UTIG), a research unit of the Jackson School of Geosciences.

“It is the third reason that seems to have had the largest impact in northwest Greenland,” said Colgan. An ‘ice bridge’ that connected Greenland to Ellesmere Island collapsed at the end of the last ice age, some 10,000 years ago.

The collapse led first to acceleration in the northwest, but ice flow there has since decreased to a slower pace. These changes affect how the Greenland Ice Sheet is understood today. Scientists often use GPS and altimeters aboard satellites to measure the elevation of the ice surface to estimate how much mass is being lost or gained across the ice sheet. But when correcting for other known effects on the surface elevation, any leftover thickening is often assumed to be due to increasing snowfall, but this study shows that may not be the case.

“The recent increases in snowfall do not necessarily explain present day interior thickening,” said Colgan. “So if you’re using a satellite altimeter to figure out how much mass Greenland is losing, you’re going to get the answer slightly wrong, unless you account for these very long-term signals that are evident in its interior.”

The study builds on earlier UTIG-led research that developed a database of the many layers within Greenland’s ice sheet. Using this database, the scientists determined the flow pattern for the past 9,000 years — in effect creating a “paleo-velocity” map.

“Scientists are very interested in understanding how ice sheets flow and how that flow may have been different in the past. Our paleo-velocity map for Greenland allows us to assess the flow of the ice sheet right now in the context of the last several thousand years,” said MacGregor.

The study was supported by the National Science Foundation’s Arctic Natural Sciences Program, the Center for Remote Sensing of Ice Sheets and NASA’s Operation IceBridge. Colgan is also a guest researcher at the Geological Survey of Denmark and Greenland, where a portion of this research was undertaken.

Note: A copy of the paper is available to media upon request.

is known for championing new ways of thinking that drive teaching and research excellence. Our 52,000 students receive the education they need to create big ideas that make an impact on the world. Meaningful and sometimes unexpected careers result from cross-discipline programming, innovative course design and diverse experiential learning opportunities. 91��ɫ students and graduates push limits, achieve goals and find solutions to the world’s most pressing social challenges, empowered by a strong community that opens minds. 91��ɫ U is an internationally recognized research university – our 11 faculties and 24 research centres have partnerships with 200+ leading universities worldwide.

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Media Contacts:
Sandra McLean, 91��ɫ Media Relations, 416-736-2100 ext. 22097 / sandramc@yorku.ca

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TORONTO, January 4, 2016 – The Greenland ice sheet has traditionally been pictured as a bit of a sponge for glacier meltwater, but new research has found it is rapidly losing the ability to buffer its contribution to rising sea levels, says a researcher.

91��ɫ U Professor , a co-author on the published today in the journal Nature Climate Change, helped analyse data from three expeditions to the Greenland ice sheet in 2012, 2013 and 2015. The research was done in conjunction with lead researcher Horst Machguth of the Geological Survey of Denmark and Greenland, Mike MacFerrin of the University of Colorado at Boulder and Dirk van As of the Geological Survey of Denmark and Greenland Copenhagen, Denmark.

Meltwater rivers on the Greenland ice sheet. Photo by Dirk van As, Geological Survey of Denmark and Greenland, Copenhagen, Denmark

Colgan spent five weeks with the team in 2013 drilling firn cores in the interior of the Greenland ice sheet. Firn is multi-year compacted snow that is not as dense as glacier ice. Instead, it forms a porous near-surface layer over the ice sheet. Dropped off by a ski-equipped US Air National Guard C-130 Hercules in minus 40 degrees Celsius weather, with 6,000 kilos of supplies and equipment, the team set up several camps and drilled a series of shallow firn cores about 20 metres deep during their time on the ice sheet.

“We were interested in the thin porous near-surface firn layer, and how its physical structure is changing rapidly with climate change,” said Colgan of the Lassonde School of Engineering. “The study looked at very recent climate change on the ice sheet, how the last couple of years of melt have really altered the structure of the ice sheet firn and made it behave differently to future melt.”

The researchers also towed a radar unit behind their skidoos to gather profiles between core sites along a 100-kilometre path from the low elevation ice sheet margin into the high elevation ice sheet interior. They analysed the firn cores on the spot by cutting them into small sections to quantify their properties, such as their density, so they could compare them with samples collected the following year. “The year-on-year firn changes were quite dramatic,” said Colgan.

The team was surprised by what they found. An extreme melt that occurred in 2012 caused a layer of solid ice, several metres thick, to form on top of the porous firn in the low elevation areas of the ice sheet. “In subsequent years, meltwater couldn’t penetrate vertically through the solid ice layer, and instead drained along the ice sheet surface toward the ocean,” said Colgan. “It overturned the idea that firn can behave as a nearly bottomless sponge to absorb meltwater. Instead, we found that the meltwater storage capacity of the firn could be capped off relatively quickly.”

As Machguth said, “Basically our research shows that the firn reacts fast to a changing climate. Its ability to limit mass loss of the ice sheet by retaining meltwater could be smaller than previously assumed.”

Because the models scientists use to project Greenland’s sea level rise contribution do not presently take firn cap-off into consideration, it means that Greenland’s projected sea level rise due to meltwater runoff is likely higher than previously predicted. Getting this newly observed physical process into these models is an important next step for the team.

Using unmanned aerial vehicles, Colgan also plans to begin surveying the changes in ice sheet surface reflectance caused by the development of massive ice layers associated with firn cap-off. There are preliminary indications that firn cap-off is also occurring in the ice caps of the Canadian High Arctic.

91��ɫ has always been known for championing new ways of thinking that drive teaching and research excellence. Our 52,000 students receive the education they need to create big ideas that make an impact on the world. ��Meaningful and sometimes unexpected careers result from cross-discipline programming, innovative course design and diverse experiential learning opportunities. 91��ɫ students and graduates push limits, achieve goals and find solutions to the world’s most pressing social challenges, empowered by a strong community that opens minds. ��91��ɫ U is an internationally recognized research university – our 11 faculties and 24 research centres have partnerships with 200+ leading universities worldwide.

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Media Contact:
Sandra McLean, 91��ɫ Media Relations, 416-736-2100 ext. 22097 /sandramc@yorku.ca

The post Climate change altering Greenland ice sheet and accelerating sea level rise, says 91��ɫ U prof appeared first on News@91��ɫ.