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)

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First results

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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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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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Including modern soot

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BC ages w ith modern soot

Modelled BC ages

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First guessStorage:500-2000 yrs

Short lived pollutants are not short lived in GreenlandResidence time to be estimated by modelling