GRL - Amount Of CO2 Emissions Irreversibly Leading To The Total Melting Of Greenland

[hatrack]

Charbit, D. Paillard, and G. Ramstein

Laboratoire des Sciences du Climat et de l'Environnement, UMR 1572, IPSL, CEA, CNRS, UVSQ,
Gif-sur-Yvette, France

Abstract

<1> The long-term response of Greenland to anthropogenic warming is of critical interest for the magnitude of the sea-level rise and for climate-related concerns. To explore its evolution over several millennia we use a climate-ice sheet model forced by a range of CO2 emission scenarios, accounting for the natural removal of anthropogenic CO2 from the atmosphere. Above 3000 GtC, the melting appears irreversible, while below 2500 GtC, Greenland only experiences a partial melting followed by a re-growth phase. Delaying emissions through sequestration slows significantly the melting, but has only a limited impact on the ultimate fate of Greenland. Its behavior is therefore mostly dependent on the cumulative CO2 emissions. This study demonstrates that the fossil fuel emissions of the next century will have dramatic consequences on sea-level rise for several millennia.

Received 30 January 2008; revised 23 April 2008; accepted 7 May 2008; published 26 June 2008.

EDIT

<10> The simulated EXP1 ice volumes highlight two different behaviors (Figure 2a). A first one is observed for the lowest scenarios (1000 to 2500 GtC) where a fast depletion rate between 2000 and 4000 AD is followed by a slower decline. After several millennia, a slight growing phase takes place, mainly due to the increase of the ice thickness (auxiliary materials, Figure S2). Nevertheless, at the end of the simulations Greenland has lost between 10 and 63% of its initial ice volume. In these simulations, the deglaciation is limited to the 60–70°N latitudinal belt, which appears to be the most sensitive to climate change (auxiliary materials, Figure S3). This contradicts the studies from Huybrechts and de Wolde <1999> and Greve <2000> who suggest that GIS first retreats to the eastern mountain ranges under warming conditions, but is in agreement with the results of Cuffey and Marshall <2000> obtained for the Eemian period which was warmer than today. Melting of the ice in the southern region greatly lowers the surface albedo, thus reducing the reflected solar energy and amplifying the net radiative heating. As a consequence, Greenland does not recover appropriate climatic conditions to induce a new glaciation process in ice-free areas, and the re-growth of the ice volume is limited to ice-covered regions even if the atmospheric CO2 concentration returns to its present-day level.

<11> The Greenland behavior obtained with the largest scenarios (3000 and 3500 GtC) is quite different (Figure 2a). The rapid phase of ice-sheet shrinkage continues until complete melting (i.e. around 11,500 and 8000 AD respectively). These two simulations have been run until the atmospheric CO2 contents recover values similar to the present-day ones, namely until 40,000 and 70,000 AD respectively. During this period, no ice-cap has been nucleated over Greenland area because the temperature increase is amplified by the reduced surface albedo. This suggests that beyond 3000 GtC, the melting of GIS is irreversible for EXP1-type scenarios.

EDIT

<13> This set of simulations reveals that complete and irreversible melting of Greenland could be avoided if the total CO2 emissions would not overcome 2500 GtC (Figure 3). Considering that the fossil fuel emissions that have been burnt up to now are around 350 GtC, policy and mitigation measures must be drastic enough so that the emissions during the next centuries are limited to ~2150 GtC. Owing to the low sensitivity of our model, this value represents an upper limit. Moreover, a number of factors are not represented, such as the radiative forcing of other greenhouse gases. Other processes, such as the evolution of permafrost that stocks large amount of carbon at depth , could have a strong influence on the global emission. In case of partial or total melting of these areas, large quantities of CO2 (and also of CH4) could be released to the atmosphere , thus lowering the critical threshold of fossil fuel emissions that leads to an irreversible melting of Greenland. Regarding the ice-sheet model, some fast processes such as the basal lubrification induced by the penetration of surface melt water, the fast flowing ice streams or the acceleration of outlet glaciers recently observed in South Greenland are not represented. Accordingly, this study probably underestimates the impact of the rapid dynamics of the Greenland ice sheet. These phenomena mainly affect the southern part of Greenland which appears to be the most sensitive in our model. On the other hand, the lack of representation of these rapid processes may be partly compensated by the use of the PDD method which may slightly overestimate the ablation . Accounting for the rapid dynamical processes and a more physically-based calculation of the Greenland surface mass balance would therefore certainly modify the timing of the simulated deglaciation but should not drastically change our conclusions concerning the influence of the rate at which CO2 is released and the critical magnitude of CO2 emissions beyond which complete melting of GIS would be irreversible. Therefore, this study clearly demonstrates that due to the long-term processes involved in the global carbon cycle or the evolution of the ice sheets, the climatic changes induced by anthropogenic activities operating on a few centuries will have large consequences for the surface of the Earth for ongoing millennia.

EDIT/END

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[Gregorian]

1. Negative carbon emissions now!

PS- Palin is actually stupider than Bush. Oh my god.

[IndyOp]

2. ...dramatic consequences on sea-level rise for several millennia

Nothing to see here folks, just be sure to tune in for this season's exciting episodes of American Idol! :applause: