Showing posts with label Claire Parkinson. Show all posts
Showing posts with label Claire Parkinson. Show all posts

Wednesday, September 19, 2012

NSIDC calls record 2012 low

This NASA satellite image shows how the Arctic sea ice extent, on Sept. 16, 2012, compares to the average
minimum extent over the past 30 years (in yellow). Credit: NASA/Goddard Scientific Visualization Studio.
Arctic sea ice cover likely melted to its minimum extent for the year on September 16, says the National Snow and Ice Data Center (NSIDC), adding the note that this number is preliminarychanging weather conditions could still push the ice extent lower.

Sea ice extent—defined by NSIDC as the total area covered by at least 15 percent of ice—fell to 3.41 million square kilometers (1.32 million square miles), now the lowest summer minimum extent in the 33-year satellite record.

NSIDC adds that this minimum is 49% below the 1979 to 2000 average, as illustrated by the table below.

Table 1. Previous minimum Arctic sea ice extents
20074.171.61September 18
20084.591.77September 20
20095.131.98September 13
20104.631.79September 21
20114.331.67September 11
20123.411.32September 16
1979 to 2000 average6.702.59September 13
1979 to 2010 average6.142.37September 15

NSIDC adds that the six lowest seasonal minimum ice extents in the satellite record have all occurred in the last six years (2007 to 2012). In contrast to 2007, when climatic conditions (winds, clouds, air temperatures) favored summer ice loss, this year’s conditions were not as extreme. Summer temperatures across the Arctic were warmer than average, but cooler than in 2007. The most notable event was a very strong storm centered over the central Arctic Ocean in early August. It is likely that the primary reason for the large loss of ice this summer is that the ice cover has continued to thin and become more dominated by seasonal ice. This thinner ice was more prone to be broken up and melted by weather events, such as the strong low pressure system just mentioned. The storm sped up the loss of the thin ice that appears to have been already on the verge of melting completely.

NASA says that this year, a powerful cyclone formed off the coast of Alaska and moved on August 5 to the center of the Arctic Ocean, where it churned the weakened ice cover for several days. The storm cut off a large section of sea ice north of the Chukchi Sea and pushed it south to warmer waters that made it melt entirely. It also broke vast extensions of ice into smaller pieces more likely to melt.

“The storm definitely seems to have played a role in this year's unusually large retreat of the ice”, said Claire Parkinson, a climate scientist at NASA Goddard Space Flight Center, Greenbelt, Md. “But that exact same storm, had it occurred decades ago when the ice was thicker and more extensive, likely wouldn't have had as prominent an impact, because the ice wasn't as vulnerable then as it is now.”

In the press release, NSIDC lead scientist Ted Scambos said that thinning ice, along with early loss of snow, are rapidly warming the Arctic. “But a wider impact may come from the increased heat and moisture the warmer Arctic is adding to the climate system,” he said. “This will gradually affect climate in the areas where we live,” he added. “We have a less polar pole—and so there will be more variations and extremes.”

The image below, from Arctic Sea Ice Blog, shows Arctic sea ice observations (in red) against the backdrop of models used in IPCC AR4 (2007) for projection of sea ice up to the year 2100.

The image below, from NSIDC sea ice news, shows the observed September sea ice extent for 1952-2011 (black line) against a backdrop of projections used by IPCC AR4 (blue) as well as proposed for use in IPCC AR5 (red).

Note: The record low value for 2012 still has to be added on this image. Credit: NSIDC, Stroeve et al.
The image shows that the recently observed decline in sea ice extent is steeper than the CMIP3 models with a “business as usual” SRESA1B greenhouse gas emissions scenario (blue line), as used by the IPCC in AR4.

It is also steeper than the more recent CMIP5 models using a RCP 4.5 scenario (pink line) that are proposed to be used by the IPCC in AR5.

RCP 4.5 is a scenario in which the global temperature rise would would soon exceed 2 degrees Celsius. Since the Arctic experiences accelerated warming, such a scenario would clearly be catastrophic. Looking at sea ice volume, rather than extent, would show this even more clearly.

Below, a NOAA animation showing sea ice decline in 2012 and a NASA animation showing the Arctic cyclone.