threatened ice sheet integrity by: carl egede bøggild the university centre in svalbard, unis...
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Threatened Ice sheet Integrity
By: Carl Egede BøggildThe University Centre in Svalbard, UNIS
Department of Arctic Geophysics
Sea level and climate sensitivity
Is the Greenland ice sheet threatened?
• yes/no/don’t know – is all true• New observational methods has
proven that past knowledge was not sufficient
• The mass balance becomes ever more negative
• No absolute method to assess the mass balance – and different methods deviate
Greenland sea level and ocean circulation
Ice sheet model predictions
An irreversible melt down may occur if around ¼ of the ice sheet mass is lost
The principle of instability
Increase in ablation area
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Dynamic effect
An overview of results
• Climate models
• Gravity satellite
• Laser altimetry
• Radar altimetry
• SAR
Why is it so difficult to measure changes?
Melt water reaching the base
Changes in calving fluxes
Is ice discharge climate or weather dependent?
Ice sheet memory: response to the LIA
Even different climate models produce different results
Increased observed surface melt
Is there a consensus?
IPCC: “loss of the Greenland ice sheet is likely not to occur in the 21st century”
Ice dynamics in the future:
-Assume that the flow accelerationwill persist unchanged-Scale up ice sheet discharge-Assume that the present imbalance is only transient
How does all this relate to short lived pollutants?
Carbon dates
y = -21.421x + 1335.5R2 = 0.7998
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Distance from margin (km)
year
bp
First results
-4000
-2000
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Distance from margin (km)
year
s
regression line ofcarbon dates
carbon age after tuning8,5 times
carbon age withcorrection for modern+50% increase for 50years
D-J model h'=0 andc=400
- Aerosols and BC remains on the ice margin surface-15% albedo reduction => 1 meter of annual melt
Results from NE-Greenland
Impurity: aerosols + micro organisms
The effect of the “agricultural revolution”
Forest clearing in North-America can potentially have caused more BC
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Distance (km)
year
s b
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BC ages
BC ages incl. AC contrib.
Model conditions: Excess BC 2 times, period 150-50 yr bp
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1875 1885 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995
10 yr. averages of industrial and charcoal soot(from Greenland ice core)
charcoal
industrial
McConnell et al. 2007. 20th-Century Industrial Black Carbon Emissions Altered Arctic Climate Forcing. Science Vol. 317. no. 5843, pp. 1381 - 1384
Modern industrial soot
Modelled BC ages
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Distance (km)
year
s b
p
Including modern soot
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Distance (km)
year
s bp BC ages
BC ages w ith modern soot
Modelled BC ages
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Distance (km)
year
s b
p
First guessStorage:500-2000 yrs
Short lived pollutants are not short lived in GreenlandResidence time to be estimated by modelling