Sunday, July 15, 2012

Arctic warming at more than double the global warming average


A new scientific study warns that the Arctic is warming at up to four times faster than the global average, due to the combination of melting sea ice and global atmospheric warming.

See also: July 2011 - Warming Arctic air temperatures causing less snow, more rain, faster ice melt | Jan 2011 - Albedo Feedback: Climate Models under estimate loss of reflectivity in the Arctic

The study warns that:

  • the Arctic troposphere has warmed at all heights, but most strongly near the surface
  • Sea ice loss and local Sea Surface Temperature (SST) changes are central to near-surface Arctic warming and
  • Remote SST changes are the main driver of Arctic warming aloft (above 700 hPa)

The study, published in Geophysical Research Letters in early July 2012, as lead by University of Melbourne researchers.

"Loss of sea ice contributes to ground level warming while global warming intensifies atmospheric circulation and contributes to increased temperatures higher in the Arctic atmosphere," said study co-author Professor Ian Simmonds from the University of Melbourne's School of Earth Sciences.

Lead author, Dr James Screen from the University of Melbourne explained the dynamics of the sea ice: "When it is heated, it reflects most of the incoming sunlight back into space. When the sea ice melts, more heat is absorbed by the water. The warmer water then heats the atmosphere above it," he said.

As temperatures increase around the globe, the intensity of atmospheric circulation also increases. "This circulation transports energy to the Arctic region, increasing temperatures further up in the atmosphere," said Professor Simmonds.

"Water vapour is a very strong greenhouse gas. As the atmosphere warms it can hold more moisture, which acts as a positive feedback signal, increasing the greenhouse effect. However, in the cold Arctic where there is less moisture in the air, this positive feedback is much weaker hence the 'direct' greenhouse effect is smaller in the Arctic than elsewhere."

"Even though the Arctic region has a relatively small greenhouse effect, the effect of the melted ice combined with greater transports of heat from the south are more than enough to make up for this modest 'local' greenhouse warming." explained Professor Simmonds.

According to the NOAA State of the Climate report card for 2011 released 10th July 2012, average Arctic temperature has increased by about 2°C in annual mean surface air temperature since the mid-1960s, which is 1.5°C greater than (more than double) the temperature increases at lower latitudes. At Barrow, Alaska there was a record 86 consecutive summer days with minimum temperatures at or above freezing. Record high temperatures were also recorded at 20 metres below the surface at all permafrost observatories on Alaska's North Slope.

The report card went on to highlight:

  • In March 2011, the lowest ozone concentrations on record led to elevated UV radiation levels at the surface.
  • September minimum sea ice extent was 2nd smallest since the satellite
    era began
  • Old ice (4-5 years) reached record low: 81% below average (see also Sea Ice volume: Multi-year arctic sea ice reducing dramatically)
  • Greenland ice sheet: Above-average air temperatures and declining albedo (reflectivity) caused extreme melting and mass loss in 2011 (see also Greenland melting in 2011 well above average with near-record mass loss)
  • All but one of the Arctic glaciers being monitored had a negative mass balance, with glaciers in Iceland very negative due to high summer air and sea surface temperatures. There was also very high glacier mass loss occurring in the eastern Alaska Range.
  • Sea surface temperature in the Beaufort, Chukchi, East Siberian, Laptev, and Kara Seas were 2nd warmest on record, behind only 2007
  • Since 1982, tundra greenness has increased by 15.5% in the North American Arctic and by 8.2% in the Eurasian Arctic

According to the report card "to date, there is no evidence that natural emissions of CH4 in the Arctic have increased significantly in the past decade (Bruhwiler and Dlugokencky 2011)"

Greenland ice sheet mass loss long term trend:

Sea Surface temperature anomaly change:

Change in summer open water and summer tundra vegetation growth:

Two charts showing the change in the albedo of the Greenland ice sheet:

The long term maximum and minimum sea ice extent trend:

The Current sea ice extent trend as of 12 July shows 2012 exceeding the record melting of sea ice set in 2007.

Sources:

  • Adapted from University of Melbourne Media release 6 July 2012 - Arctic warming linked to combination of reduced sea ice and global atmospheric warming
  • J. A. Screen, C. Deser, I. Simmonds. Local and remote controls on observed Arctic warming ((abstract) Geophysical Research Letters, 2012; 39 (10) DOI: 10.1029/2012GL051598
  • Blunden, J., and D. S. Arndt, Eds., 2012: State of the Climate in 2011. Bull. Amer. Meteor. Soc., 93 (7), S1-S264.
  • Images of charts from M. O. Jeffries and J. Richter-Menge, Eds., 2012: The Arctic [in "State of the Climate in 2011"]. Bull. Amer. Meteor. Soc., 93 (7), S127-148. except current Sea Ice extent from the National Snow and Ice Data Centre 12 July 2012