Earth & Environment - Posted by Louise Bennet-Melbourne on Friday, July 6, 2012 10:43 - 0 Comments
‘Shiny lid’ of sea ice spikes Arctic heat
U. MELBOURNE (AUS) — The combination of melting sea ice and global atmospheric warming is contributing to a high rate of warming in the Arctic, where temperatures are rising up to four times faster than the global average, a new study shows.
Published in the journal Geophysical Research Letters, new information shows how this combined effect at both ground and atmospheric level plays a key role in increasing the rate of warming in the Arctic.
“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,” says Ian Simmonds, professor of earth sciences at the University of Melbourne.
Straight from the Source
The sea ice acts like a shiny lid on the Arctic Ocean, says lead author James Screen. “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.”
As temperatures increase across the globe, so does the intensity of atmospheric circulation, Simmonds says. “This circulation transports energy to the Arctic region, increasing temperatures further up in the atmosphere.
“Water vapor 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.”
The study was also featured in Nature.
More news from the University of Melbourne: http://newsroom.melbourne.edu/