Is Arctic sea ice back to normal?

Arctic sea ice was at record highs in the Bering Sea this spring, and near the long-term average for the Arctic as a whole. But much of that ice was spread thinly across the ocean, and is now melting quickly. This image, from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS), shows sea ice in Bristol Bay off of Alaska, on April 24, 2012. |Credit: {a href=http://earthobservatory.nasa.gov/IOTD/view.php?id=77832}NASA Earth Observatory{/a} image by Jesse Allen|{a href=http://nsidc.org/icelights/files/2012/05/bristolbay_amo_2012115_lrg.png}High Resolution Image{/a}

In April, average ice extent in the Arctic Ocean was right near the long-term average for the month. Ice extent even reached a near-record high in the Bering Sea, and still remains above average for that region. Does this mean that the Arctic sea ice has stopped declining? Is it starting to recover?

Unfortunately, scientists say no—and they are not surprised to see such a short upward bump in ice extent. “This does not indicate that the Arctic sea ice is recovering,” said Marika Holland, a sea ice expert at the National Center for Atmospheric Research (NCAR). Instead, the higher ice extent this year compared to recent years likely just reflects different weather this winter compared to last winter.  “Sea ice exhibits large natural variability due to year-to-year variations in weather,” she said.

While the ice cover was relatively extensive at the end of winter, much of that is made up of dispersed floes spread thinly across the ocean surface. NSIDC scientist Walt Meier said, “While extent briefly reached the average, the amount of thicker, older ice has remained far below normal, as has the total ice volume.” That means that the extensive ice will likely melt away quickly once temperatures warm up. Indeed, this melt has already started in the Beaufort Sea, and to some extent in the Bering Sea. For current conditions see Arctic Sea Ice News & Analysis.

This graph shows average sea ice extent for the month of April from 1979 to 2012. Average Arctic sea ice extent for April, 2012, was the highest it had been in the last ten years, and near the long-term average for the month. But researchers caution against jumping to the conclusion that ice has recovered. Credit: NSIDC

Bumps on a line
Year-to-year changes caused by weather are one reason that researchers look at long-term data when calculating trends, instead of short-term changes. Climate scientists expect that while sea ice will continue to decline, that decline won’t be like a smooth slide down a ski slope. Instead, the decline is more like the terrain park—while the overall slope moves downward, a skier will bounce and jump around on her way to the bottom.

Holland has worked extensively on climate models that try to predict how sea ice will behave in the future. She said, “We expect reductions of sea ice over the long-term, punctuated by shorter-term variations of either minimal or extreme ice loss.” Holland and her colleagues recently published a study showing that ice could increase for periods of up to ten years, even as climate change continues to warm the Arctic and the long-term trend continues to decline.

Could ice get back to normal?
Though scientists are convinced that the long-term trend for sea ice continues downward, is it possible that Arctic sea ice could recover? Holland said, “Experiments with climate models suggest that Arctic sea ice could recover with reductions in atmospheric greenhouse gas concentrations.”

What would a recovery look like? Arctic sea ice is now thinner than it used to be, and melts more easily in the summer. Meier said, “For a true recovery we would need to see the amount of thick ice increase back to its previous levels.” Getting Arctic sea ice to thicken up again will take more than one cold weather pattern and more than one near-normal winter.

 

References

Kay, J. E., M. M. Holland, and A. Jahn. 2011. Inter-annual to multi-decadal Arctic sea ice extent trends in a warming world. Geophys. Res. Lett., 38, L15708, doi:10.1029/2011GL048008. http://www.agu.org/pubs/crossref/2011/2011GL048008.shtml

 

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