NSIDC 7/18 - Early Sea Ice Melt Onset, Snow Retreat Presage Rapid 2011 Summer Decline

[hatrack]

Arctic sea ice extent declined at a rapid pace through the first half of July, and is now tracking below the year 2007, which saw the record minimum September extent. The rapid decline in the past few weeks is related to persistent above-average temperatures and an early start to melt. Snow cover over Northern Eurasia was especially low in May and June, continuing the pattern seen in April.

Overview of conditions
As of July 17, 2011, Arctic sea ice extent was 7.56 million square kilometers (2.92 million square miles), 2.24 million square kilometers (865,000 square miles) below the 1979 to 2000 average. Sea ice is particularly low in the Barents, Kara, and Laptev Seas (the far northern Atlantic region), Hudson Bay and Baffin Bay.


Figure 1. Arctic sea ice extent on July 17, 2011 was 7.56 million square kilometers (2.92 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole.

Conditions in context
Arctic sea ice extent declined rapidly through the first two weeks of July, at a rate averaging nearly 120,000 square kilometers (46,000 square miles) per day. Ice extent is now tracking below the year 2007, which saw the record minimum September extent.

During the first half of July, a high-pressure cell persisted over the northern Beaufort Sea, as it did in June, and is linked to the above-average air temperatures over much of the Arctic Ocean. To date in July, air temperatures over the North Pole (at the 925 millibar level, or roughly 1,000 meters or 3,000 feet above the surface) were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) higher than normal, while temperatures along the coasts of the Laptev and East Siberian seas were 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) higher than average. By contrast, temperatures through the first half of July over the Kara Sea have been 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) lower than average.


Figure 2. The graph above shows daily Arctic sea ice extent as of July 17, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, and dark gray shows the 1979 to 2000 average. The gray area around the average line shows the two standard deviation range of the data.

A closer look at sea ice concentration
The sea ice extent data that NSIDC uses come from the Special Sensor Microwave Imager/Sounder (SSMIS) on U.S. Department of Defense satellites. Data from other satellites, while not as useful for studying long-term trends, can show more detail about ice cover in particular regions. Currently data from two NASA satellite sensors, the Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer for EOS (AMSR-E), show areas of low ice concentration north of Alaska. Ice in these areas is likely to melt out in coming weeks.

Both the Northwest Passage (through the channels of the Canadian Arctic Islands) and the Northern Sea Route (along the Siberian coast) are still choked with ice.


Figure 3. Satellite images from the NASA AMSR-E sensor (large image) and MODIS (inset), show areas of low ice concentration north of Alaska. Both images were obtained on July 15, 2011. In the AMSR-E image, purple indicates areas of high sea ice concentration, while yellow and red indicates lower ice concentration. Blue shows open water and green shows land.

Early start to Arctic melt
When sea ice starts to melt in spring, small ponds known as melt ponds form on its surface. The small pools create a darker surface (a lower albedo) that fosters further melt. How early sea ice melt starts is one indicator of how much the ice will melt in a given year. New research by Don Perovich and colleagues shows that an early start to sea ice melt increases the total amount of sunlight absorbed through the melt season.

Data processed by researchers Thorsten Markus and Jeffrey Miller at the NASA Goddard Space Flight Center reveal that melt began earlier than normal in both the Chukchi Sea, just north of the Bering Strait, and the Barents, Kara, and Laptev seas. Surface melting on the sea ice began from two weeks to two months earlier than the 1979 to 2000 average in these areas. However, in Baffin Bay and Hudson Bay, a cool spring led to a later start for surface melt, especially in Hudson Bay. Subsequent warm conditions have nevertheless led to rapid ice melt.


Figure 4. This map shows the difference between average date of melt onset, when ice melt starts, and the date of melt onset this year. Red indicates earlier than normal melt, blue shows later than normal melt. The darkest red is an anomaly of 50 days early or more. White areas show no anomaly, that is they melted no earlier or later than normal. The gray area over the North Pole indicates where no data are available.

Low summer snow cover in the Northern Hemisphere
As noted in our May 4 post, snow cover in central Russia retreated early in response to warm conditions this spring. Updated analyses provided by the Global Snow Cover Lab at Rutgers University reveal that snow cover remained very low for May and June. Even though some mountain regions in the U.S. and Canada saw greater-than-normal snow cover, snow cover for the Northern Hemisphere as a whole for May and June was the second lowest since the start of snow cover records in 1966.

According to David Robinson, head of the Rutgers Snow Cover Lab, a new pattern is emerging in which the Northern Hemisphere is cloaked in above-average snow during late autumn, winter, and early spring, followed by rapid melt and retreat in May and June. While snow cover varies from year to year, the far north has seen a clear trend towards less spring snow cover over the last thirty years.


Figure 5. This snow cover anomaly map for May and June, 2011 shows the percent difference between snow cover extent this summer, compared with average snow cover for May and June 1971 to 2000. Areas in orange and red indicate lower-than-usual snow cover, while regions in blue had more snow than normal.

Further Reading

The July report of the ARCUS Sea Ice Outlook is now available . The report, compiled from sixteen international groups of sea ice scientists and others, predicts that September sea ice extent will fall well below the average for the month. However, only three of the sixteen predictions call for a September extent that breaks the 2007 record.

Do you have questions about the upcoming Arctic sea ice minimum extent? Read Heading towards the summer minimum ice extent, on NSIDC's new Icelights: Your burning questions about ice and climate.

References

Markus, T., J. C. Stroeve, and J. Miller. 2009 Recent changes in Arctic sea ice melt onset, freezeup, and melt season length, J. Geophys. Res., 114, C12024, doi:10.1029/2009JC005436.

Kunkel, K. E., M. Palecki, L. Ensor, K. G. Hubbard, D. Robinson, K. Redmond, D. Easterling. 2009. Trends in Twentieth-Century U.S. Snowfall Using a Quality-Controlled Dataset. J. Atmos. Oceanic Technol., *26*, 33–44. doi: 10.1175/2008JTECHA1138.1

Ghatak, D., A. Frei, G. Gong, J. Stroeve, and D. Robinson. 2010. On the emergence of an Arctic amplification signal in terrestrial Arctic snow extent, J. Geophys. Res., 115, D24105, doi:10.1029/2010JD014007.

Perovich, D.K., K.F. Jones, B. Light, H. Eicken, T. Markus, J. Stroeve, R. Lindsay. 2011. Solar partitioning in a changing Arctic sea-ice cover, Annals of Glaciology, 52(57), 192-196.

For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.

EDIT/END

http://www.nsidc.org/arcticseaicenews/index.html

[pscot]

1. The temperature anomalies

really leap out.

[emmadoggy]

2. K & R. nt

[joshcryer]

3. Capitalism is about to have one hell of a boon.

:cry:

[txlibdem]

4. It's been like watching the movie 2012 in ultra-ultra-slow motion

And, just as in the movie, the rich think they're going to emerge from the disaster they've created without a scratch.

Shall we allow them to?

[joshcryer]

5. Unlikely we'll be able to reverse the sea ice melt, so the northwest passage *will* be open.

And the capitalists are going to love the hell out of it. Point of no return has very likely been reached. Probably reached it a decade ago.

[txlibdem]

6. I misunderstood your earlier post

So you're saying this global climate change stuff is going to be a good thing?