The $1,000 bet on "Ice free Arctic"

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A FOOTNOTE

GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L08503, doi:10.1029/2008GL033451, 2008

The contribution of cloud and radiation anomalies to the 2007 Arctic sea ice extent minimum

Jennifer E. Kay
Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA
Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA

Tristan L'Ecuyer
Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA

Andrew Gettelman
Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA

Graeme Stephens
Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA

Chris O'Dell
Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA

Abstract

Reduced cloudiness and enhanced downwelling radiation are associated with the unprecedented 2007 Arctic sea ice loss. Over the Western Arctic Ocean, total summertime cloud cover estimated from spaceborne radar and lidar data decreased by 16% from 2006 to 2007. The clearer skies led to downwelling shortwave (longwave) radiative fluxes increases of +32 Wm−2 (−4 Wm−2) from 2006 to 2007. Over three months, simple calculations show that these radiation differences alone could enhance surface ice melt by 0.3 m, or warm the surface ocean by 2.4 K, which enhances basal ice melt. Increased air temperatures and decreased relative humidity associated with an anti-cyclonic atmospheric circulation pattern explain the reduced cloudiness. Longer-term observations show that the 2007 cloudiness is anomalous in the recent past, but is not unprecedented. Thus, in a warmer world with thinner ice, natural summertime circulation and cloud variability is an increasingly important control on sea ice extent minima.

ANOTHER FOOTNOTE

GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L07502, doi:10.1029/2007GL032630, 2008

Twentieth century Antarctic air temperature and snowfall simulations by IPCC climate models

Andrew J. Monaghan

Polar Meteorology Group, Byrd Polar Research Center, Ohio State University, Columbus, Ohio, USA

David H. Bromwich

Polar Meteorology Group, Byrd Polar Research Center, Ohio State University, Columbus, Ohio, USA
Atmospheric Sciences Program, Department of Geography, Ohio State University, Columbus, Ohio, USA

David P. Schneider

Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA

Abstract

We compare new observationally-based data sets of Antarctic near-surface air temperature and snowfall accumulation with 20th century simulations from global climate models (GCMs) that support the Intergovernmental Panel on Climate Change Fourth Assessment Report. Annual Antarctic snowfall accumulation trends in the GCMs agree with observations during 1960–1999, and the sensitivity of snowfall accumulation to near-surface air temperature fluctuations is approximately the same as observed, about 5% K−1. Thus if Antarctic temperatures rise as projected, snowfall increases may partially offset ice sheet mass loss by mitigating an additional 1 mm y−1 of global sea level rise by 2100. However, 20th century (1880–1999) annual Antarctic near-surface air temperature trends in the GCMs are about 2.5-to-5 times larger-than-observed, possibly due to the radiative impact of unrealistic increases in water vapor. Resolving the relative contributions of dynamic and radiative forcing on Antarctic temperature variability in GCMs will lead to more robust 21st century projections.

The Arctic ocean is warming up, icebergs are growing scarcer and in some places the seals are finding the water too hot, according to a report to the Commerce Department yesterday from Consul Ifft, at Bergen, Norway.