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IPCC models underestimate future sea ice loss - New scientific paper

  • 06 Oct 2011, 15:00
  • Verity Payne

© Lars Witting/ARC-PIC.COM

 IPCC climate models do not capture Arctic sea ice drift acceleration: Consequences in terms of projected sea ice thinning and decline

A new paper in the Journal of Geophysical Research offers fresh insights into Arctic sea ice. Researchers compared observations of Arctic sea ice with projections from IPCC models. Arctic sea ice thins and drifts faster in the summer months, accelerating sea ice decline. The paper finds that IPCC climate models underestimate observed Arctic sea ice loss, particularly thinning trends. This means that the IPCC projections for ice-free Arctic summer seas by 2100 are likely to be too conservative.

Background:

Arctic sea ice varies seasonally (growing in winter and retreating in summer) but satellite records over the last three decades show an overall decline in sea ice extent. The Arctic is thought to be warming at around twice the global rate. This is thought primarily to be because ice reflects incoming solar energy - loss of ice reduces this reflection, leading to greater regional warming. Sea ice loss has been accelerating over the last few years, faster than projected by IPCC AR4 models.

Abstract:

"IPCC climate models underestimate the decrease of the Arctic sea ice extent. The recent Arctic sea ice decline is also characterized by a rapid thinning and by an increase of sea ice kinematics (velocities and deformation rates), with both processes being coupled through positive feedbacks. In this study we show that IPCC climate models underestimate the observed thinning trend by a factor of almost 4 on average and fail to capture the associated accelerated motion. The coupling between the ice state (thickness and concentration) and ice velocity is unexpectedly weak in most models. In particular, sea ice drifts faster during the months when it is thick and packed than when it is thin, contrary to what is observed; also models with larger long-term thinning trends do not show higher drift acceleration. This weak coupling behavior (1) suggests that the positive feedbacks mentioned above are underestimated and (2) can partly explain the models' underestimation of the recent sea ice area, thickness, and velocity trends. Due partly to this weak coupling, ice export does not play an important role in the simulated negative balance of Arctic sea ice mass between 1950 and 2050. If we assume a positive trend on ice speeds at straits equivalent to the one observed since 1979 within the Arctic basin, first-order estimations give shrinking and thinning trends that become significantly closer to the observations."

Citation and link:

Rampal, P., J. Weiss, C. Dubois, and J.-M. Campin (2011), IPCC climate models do not capture Arctic sea ice drift acceleration: Consequences in terms of projected sea ice thinning and decline, J. Geophys. Res., 116, C00D07, doi:10.1029/2011JC007110.

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