Melting sea ice and global atmospheric warming are making the Arctic warm as much as four times faster than the global average, Australian scientists say.
A new University of Melbourne study has shown that 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.
Sea ice acts like a shiny lid on the Arctic Ocean, says Dr James Screen of the university’s School of Earth Sciences.
“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 says.
And as temperatures increase across the globe, so does the intensity of atmospheric circulation. This circulation transports energy to the Arctic region, increasing temperatures further up in the atmosphere.
“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,” says professor Ian Simmonds.
“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.”