The widespread decline in Arctic sea ice is causing big changes to the balance of greenhouse gases in the atmosphere, say researchers from Sweden's Lund University.
The melting of sea ice in the Arctic has a tangible impact on the balance of carbon dioxide and methane, both in the tundra and in the Arctic Ocean, they say.
“Changes in the balance of greenhouse gases can have major consequences because, globally, plants and the oceans absorb around half of the carbon dioxide that humans release into the air through the use of fossil fuels," says Dr Frans-Jan Parmentier. "If the Arctic component of this buffer changes, so will the amount of greenhouse gases in the atmosphere."
Normally, the white ice reflects sunlight, which then bounces out into space, but when the sea-ice cover shrinks, the amount of sunlight reflected is also reduced. Instead, a larger proportion is absorbed by the surface of the ocean, which causes warming that contributes to the rise in air temperatures around the Arctic.
There is a small positive effect, as rising temperatures make vegetation grow more vigorously and take up more CO2. However, the same temperature rise means that more carbon dioxide and methane are released from the soil, which has a strong negative impact on the climate.
And there are changes in the ocean too - although these are less well understood. "We know very little about how the shrinking sea ice cover disturbs the balance of greenhouse gases in the sea in the long term," says Parmentier.