Friday, March 25, 2011
Thursday, March 10, 2011
By Bronwyn Herbert
Wednesday, March 9, 2011
Saturday, March 5, 2011
Wednesday, March 2, 2011
By Karen Barlow
Major ecosystem shifts
NSIDC, March 2, 2011
Overview of conditions
Sea ice extent averaged over the month of February 2011 was 14.36 million square kilometers (5.54 million square miles). This was a tie with the previous record low for the month, set in 2005. February ice extent remained below normal in both the Atlantic and Pacific sectors, particularly in the Labrador Sea and the Gulf of St. Lawrence.
While ice extent has declined less in winter months than in summer, the downward winter trend is clear. The 1979 to 2000 average is 15.64 million square kilometers (6.04 million square miles). From 1979 through 2003, the February extent averaged 15.60 million square kilometers (6.02 million square miles). Every year since 2004 has had a mean February extent below 15 million square kilometers (5.79 million square miles).
Conditions in context
While ice extent grew at average rates for February, the overall extent remained anomalously low. Air temperatures over most of the Arctic Ocean were between 2 and 4 degrees Celsius (4 and 7 degrees Fahrenheit) higher than normal. Over the East Greenland Sea and north towards the Pole, air temperatures were 5 to 7 degrees Celsius (9 to 13 degrees Fahrenheit) higher than normal. Colder conditions, 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) below average persisted over western Eurasia, east-central Eurasia and some of the Canadian Arctic.
As air temperatures dropped in the eastern Canadian Arctic in February, parts of the Labrador Sea started to freeze over. However, the Gulf of St. Lawrence remained mostly free of ice. As during winter 2010, when Environment Canada reported that sea ice in the Gulf of St. Lawrence was at the lowest level on record, the lack of ice will make it difficult for harp seals to give birth to their pups on the sea ice, as they normally do in February and March.
February 2011 tied February 2005 for the lowest ice extent for the month in the satellite record. Including 2011, the February trend is now at -3.0 percent per decade.
Through most of January, the Arctic Oscillation (AO) was generally in a strongly negative phase, similar to the pattern that dominated the winter of 2009 to 2010. This led to very warm temperatures over the eastern Arctic, helping to account for the low ice extents over the Labrador Sea and Gulf of Saint Lawrence. However, toward the end of January, the AO returned to a positive phase, and ice began to grow in the Labrador Sea and Gulf of St. Lawrence. For more information on current AO conditions, visit the NOAA Climate Prediction Center Web page.
Typically during a negative AO phase, weather patterns favor the retention of thick ice in the central Arctic and Canada basin, where it can better survive the summer. The negative AO also typically leads to a stronger Beaufort Gyre, which helps move ice from the western to eastern Arctic. There the ice thickens, ridging and rafting against the Siberian coast.
Last winter, the AO was in its most negative phase since at least 1951. However, slight differences from the typical AO pattern in the location of the sea level pressure anomalies had a significant impact on how the ice moved within and out of the Arctic Basin. During winter 2009 to 2010 the peak pressure anomalies were shifted towards the Barents and Kara seas, which helped transport ice from the Canadian Arctic towards the southern Beaufort and Chukchi seas. Since some of the oldest and thickest ice in the Arctic is found north of the Canadian Archipelago, this atmospheric pattern ended up further depleting the Arctic of its store of old, thick ice as that old ice melted during summer in these southerly locations.
This winter also saw a relatively strong negative AO index during December and January. However, as we discussed in our January 5, 2011 post, the positive sea level pressure anomalies were centered near Iceland. This led to a more extensive anticyclonic (clockwise) transport pattern than last winter. This may help keep a more extensive distribution of multiyear ice cover as summer approaches.
January and February Northern Hemisphere snow cover
Sea ice extent is only one of a number of data sets scientists use to understand how climate is changing. Rutgers University and NOAA have compiled a 45-year record of Northern Hemisphere snow cover extent from NOAA snow charts. These data show that much of northern North America, Scandinavia and northern Eurasia are snow covered between 90 and 100 percent of the time in January and February. High elevation plains and mountains at lower latitudes, such as the southern Rocky Mountains in the U.S. and Hindu Kush in Asia, also have extensive snow cover.
Over this record, in January, Northern Hemisphere snow cover averages 47 million square kilometers (18.1 million square miles), and in February it averages 46 million square kilometers (17.8 square miles)—approximately 45 to 46 percent of the land area in the region. While sea ice extent was below average for January 2011, this month had the sixth-largest snow cover extent since the record started in 1966, at 49 million square kilometers (18.9 million square miles). Snow was unusually widespread over the mid-western and eastern United States, eastern Europe, and western China. Snow cover in February remained above average at 47.4 million square kilometers (18.3 million square miles), with more snow than usual in the western and central U.S., eastern Europe, Tibet and northeastern China.
Reduced sea ice extent and extensive snow cover are not contradictory, and are both linked to a strong negative phase of the Arctic Oscillation (see our January 5, 2011 post). A strongly negative AO favors outbreaks of cold Arctic air over northern Europe and the U.S., as many people experienced first-hand these last two winters. Whether this is a trend, or in any way linked to ongoing climate warming in the Arctic, remains to be seen.
Stroeve, J.C., J. Maslanik, M.C. Serreze, I. Rigor and W. Meier. 2010. Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010. Geophysical Research Letters, doi: 2010GL045662.
Deborah Zabarenko, Environment Correspondent
(Reuters) - This winter's heavy snowfalls and other extreme storms could well be related to increased moisture in the air due to global climate change, a panel of scientists said on Tuesday.
This extra moisture is likely to bring on extraordinary flooding with the onset of spring in the Northern Hemisphere, as deep snowpack melts and expected heavy rains add to seasonal run-off, the scientists said in a telephone briefing.
As the planet warms up, more water from the oceans is evaporated into the atmosphere, said Todd Sanford, a climate scientist at the Union of Concerned Scientists. At the same time, because the atmosphere is warmer, it can hold onto more of the moisture that it takes in.
Intense storms are often the result when the atmosphere reaches its saturation point, Sanford said.
This year, a series of heavy storms over the U.S. Midwest to the Northeast have dropped up to 400 percent of average snows in some locations, said Jeff Masters, director of meteorology at Weather Underground.
The amount of water in that snowpack is among the highest on record, Masters said.
"If you were to take all that water and melt it, it would come out to more than 6 inches over large swaths of the area," Masters said. "If all that water gets unleashed in a hurry, in a sudden warming, and some heavy rains in the area, we could be looking at record flooding along the Upper Mississippi River and the Red River in North Dakota."
That tallies with projections by the U.S. National Weather Service, which last month said a large stretch of the north central United States is at risk of moderate to major flooding this spring.
Spring floods could be exacerbated by spring creep, a phenomenon where spring begins earlier than previously.
"We've documented in the mountains of the U.S. West that the spring runoff pulse now comes between one and three weeks earlier than it used to 60 years ago," Masters said. "And that's because of warmer temperatures tending to melt that snowpack earlier and earlier."
In the last century, global average temperatures have risen by 1.4 degrees Fahrenheit (.8 Celsius). Last year tied for the warmest in the modern record. One place this warmth showed up was in the Arctic, which is a major weather-maker for the Northern Hemisphere, according to Mark Serreze, director of the U.S. National Snow and Ice Data Center.
One driver of this winter's "crazy weather," Serreze said, is an atmospheric pattern known as the Arctic Oscillation, which has moved into what climate scientists call a negative phase.
This phase means there is high pressure over the Arctic and low pressure at mid-latitudes, which makes the Arctic zone relatively warm, but spills cold Arctic air southward to places like the U.S. Midwest and Northeast.
This negative Arctic Oscillation has been evident for two years in a row, the same two winters that have had extreme storms and heavy snowfalls.
The only underlying explanation for these events is climate warming due to heightened greenhouse gas levels, Serreze said.
(Editing by Mohammad Zargham)