Ice-Atmosphere Interaction (2):

Melting of Greenland Ice Sheet

By: Eric DoBroka

Professor Edward HannaProfessor of Climate Change

-Edward Hanna received a BS in Planetary Science (First Class Honors) from University College London in 1995

-He was appointed as lecturer in climate change in 2003 in Sheffield, UK -Member of both Meteorological and Astronomical Societies; International Glaciological Society

-Published over 80 research papers

-Got questions? Call +44-144-222-7965

Increased Runoff from Melt from the Greenland Ice Sheet: A Response to Global Warming

(2008)

Greenland IS Going Green!!

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Attributes significant ice melt for 3 reasons:

1) Increased Summertime Temperatures (Numerous records smashed)

2) Significant Increasing Trend in Water Runoff

3) Change in NAO from positive to less positive/more neutral state

Where’d all the ice go??

Topography of Greenland

1) Increased Summertime Temperatures

Top 10 Warmest Summers in Southern Greenland

2) Excessive Water Runoff

1998, 2003, and 2006 were respectively the first, second, and third highest runoff years

5 highest runoff years have all occurred since 1995

During these years, significant 24.3% increase in runoff (113 cubic km as opposed to the standard deviation of 68.7 cubic km)

3) Changing of the North Atlantic Oscillation

Breaks down after the early 1990s

Changes in atmospheric circulation (jet Streams)

Positive Phase for most of period between 1960s and 1980s

More neutral phase

Less positive state reduced the insularity of Greenland by encouraging WAA over land masses

Conclusions Both Greenland and the Northern Hemisphere summer

temperatures exhibit common strong warming trends since the early 90s

Period of temperature recovery from volcanic eruptions Significant glacier melting is in fact taking place at an

alarming rate Uncertainties: As observed since 1987 at Summit,

summer temps near top of the ice sheet have declined slightly

Dichotomous Response due to high thermal inertia, higher atmospheric cooling, or changes in wind, cloud, radiation patterns?

Aud Venke Sundal

University of Leeds (UK)

Several publications on changingclimate, glaciers; effectson Norway

Geological Mapping (GIS)

“Aud Venke Sundal.”- I Norge er mye av løsmassene avsatt av rennende vann. Slike masser består av grov sand og grus med lite finstoff, noe som gjør at radongassen som blir

Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage (2011)

Fluctuations in surface melting effects speeds of glaciers and ice sheets

Impact of warming climate decreases acceleration of Greenland’s flow despite melting??

Satellite observations of ice motion in SW Greenland

Rates of ice speed positively correlated w/ degree of melting; mean flow rates are NOT

Warmer years, ice flow is 3x shorter; overall flow slower

Explored spatial and temporal variations comparing velocities Overall, significant

flow increase in summer for all 6 glaciers w/ speed-ups of 50% to 125%

Seasonal surface melting drives seasonal cycles in ice sheet flow

Dependent upon altitude

Mirrors mountain glaciersMelt induced

acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient!!

Video Clip of Greenland Ice Melt

https://www.youtube.com/watch?v=b4QjyrGkaUg

Conclusions Data shows that subglacial drainage system

in SW Greenland evolves in response to variable surface melting similar to mountain glaciers.

Rates of surface melting at the Greenland ice sheet are predicted to double

over the course of this century. Would add .15m to .4m in sea level rise

Conclusions Cont. BUT….their data is first to

indicate a drop in summer speed-up of glaciers in years of high melting compared to years of low melting

Supports views that subglacial drainage system may adjust to accommodate increased melting

Uncertainties “The net effect of melt-

induced speed-up and efficient drainage remains uncertain.”

Let’s Play 20 QuestionsNo really let’s not