Massachusetts Institute of Technology researchers explain why global warming has led to Arctic losing sea ice, but the same has not been observed in Antarctica.

Over the past few years, Arctic has shown considerable reduction in sea ice levels due to global warming. However, Antarctica has cooled and has even gained some ice recently. A new study suggests that ocean circulation can explain why the polar regions have different reactions towards rise in earth's temperature.

John Marshall, the Cecil and Ida Green Professor of Oceanography at MIT and colleagues used computer models to see how ocean dynamics is changing the effects of global warming.

MIT scientists found that Southern Ocean and North Atlantic Ocean absorbs excess heat from greenhouse gas emissions. But the heat doesn't stay there; instead, oceanic circulation redistributes the heat around the equator.

In the Southern Ocean, strong, northward-flowing currents send the heat to the equator, while northward-flowing current system in the Northern Atlantic takes the heat towards the Arctic. The study shows that oceanic currents redistribute the heat in such a way that Arctic experiences accelerated warming, while Antarctica warms up mildly.

The study even found that the ozone hole over the Antarctica has briefly paused sea ice loss in the region. Scientists said that when they accounted for the ozone hole in their model, they found that  winds over the Southern Ocean grew faster and shifted southwards. These winds initially cool the area. But, the process eventually begins to warm the Antarctic and shrinks the ice cover.

"Around Antarctica, the ozone hole may have delayed warming due to greenhouse gases by several decades," Marshall said in a news release. "I'm tempted to speculate that this is the period through which we are now passing. However, by 2050, ozone hole-effects may instead add to the warming around Antarctica, an effect that will diminish as the ozone hole heals."

"The researchers present a useful and timely reminder that the ocean is not a passive bath tub when it comes to climate change, but play an active role in shaping the spatial structure of climate change," said Richard Seagar, the Palisades Geophysical Institute/Lamont Research Professor at the Lamont-Doherty Earth Observatory, who was not involved in the study.

The study is published in the journal Philosophical Transactions of the Royal Society.