Transcript Ice-Atmosphere Interaction (2): Melting of Greenland Ice Sheet

Ice-Atmosphere
Interaction (2): Melting
of Greenland Ice Sheet
By: Eric DoBroka
Professor Edward Hanna
Professor 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!!
Where’d all the ice go??

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
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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 changing
climate, glaciers; effects
on Norway
Geological Mapping (GIS)
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/ speedups of 50% to 125%

Seasonal surface
melting drives seasonal
cycles in ice sheet flow

Dependent upon
altitude
 Mirrors
mountain
glaciers
Melt
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 meltinduced speed-up and
efficient drainage remains
uncertain.”
Let’s Play 20 Questions
No really let’s not