By Anthony Watts

From the AGU Journal Highlights, some news that NSIDC’s “death spiral” has zombie like characteristics, and that the ice may quickly return from the dead, even if the Arctic turned ice free during summer. Nature is more resilient it seems, than some people give it credit for.

What an ice free Arctic might look like from space

No tipping point for Arctic Ocean ice, study says

Declines in the summer sea ice extent have led to concerns within the scientific community that the Arctic Ocean may be nearing a tipping point, beyond which the sea ice cap could not recover. In such a scenario, greenhouse gases in the atmosphere trap outgoing radiation, and as the Sun beats down 24 hours a day during the Arctic summer, temperatures rise and melt what remains of the polar sea ice cap. The Arctic Ocean, now less reflective, would absorb more of the Sun’s warmth, a feedback loop that would keep the ocean ice free.

However, new research by Tietsche et al. suggests that even if the Arctic Ocean sees an ice-free summer, it would not lead to catastrophic runaway ice melt.

The researchers, using a general circulation model of the global ocean and the atmosphere, find that Arctic sea ice recovers within 2 years of an imposed ice-free summer to the conditions dictated by general climate conditions during that time. Furthermore, they find that this quick recovery occurs whether the ice-free summer is triggered in 2000 or in 2060, when global temperatures are predicted to be 2 degrees Celsius (3.6 degrees Fahrenheit) warmer.

During the long polar winter the lack of an insulating ice sheet allows heat absorbed by the ocean during the summer to be released into the lower atmosphere. The authors find that increased atmospheric temperatures lead to more energy loss from the top of the atmosphere as well as a decrease in heat transport into the Arctic from lower latitudes. So the absence of summer sea ice, while leading to an increase in summer surface temperatures through the ice-albedo feedback loop, is also responsible for increased winter cooling. The result is a swift recovery of the Arctic summer sea ice cover from the imposed ice-free state.

Title: “Recovery mechanisms of Arctic summer sea ice”
Authors: S. Tietsche, D. Notz, J. H. Jungclaus, and J. Marotzke
Max Planck Institute for Meteorology, Hamburg, Germany
Source: GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L02707, 4 PP., 2011 doi:10.1029/2010GL045698

We examine the recovery of Arctic sea ice from prescribed ice-free summer conditions in simulations of 21st century climate in an atmosphere-ocean general circulation model. We find that ice extent recovers typically within two years. The excess oceanic heat that had built up during the ice-free summer is rapidly returned to the atmosphere during the following autumn and winter, and then leaves the Arctic partly through increased longwave emission at the top of the atmosphere and partly through reduced atmospheric heat advection from lower latitudes. Oceanic heat transport does not contribute significantly to the loss of the excess heat. Our results suggest that anomalous loss of Arctic sea ice during a single summer is reversible, as the ice-albedo feedback is alleviated by large-scale recovery mechanisms. Hence, hysteretic threshold behavior (or a “tipping point") is unlikely to occur during the decline of Arctic summer sea-ice cover in the 21st century. Post.