NewScientist: Antarctic wind vortex is strongest for 1,000 years

The winds ripping around Antarctica. (Image: earth.nullschool.net)

by Michael Slezak, NewScientist, May 11, 2014 

Our greenhouse gas emissions are helping to spin up a giant vortex of winds around Antarctica.

Antarctica has been warming relatively slowly compared with the rest of the world. The explanation seems to be that the winds spinning clockwise around the continent have been getting stronger, preventing warm air from entering.

In a way, those winds have done us a favour by keeping warm air away from the South Pole. Otherwise it might be melting. But as this atmospheric maelstrom accelerates, it shrinks, leaving the most vulnerable parts of Antarctica out in the warm and dragging winter rain away from Western Australia.

In 2009, it seemed that the hole in the ozone layer above Antarctica was responsible for boosting the winds. Now Nerilie Abram from the Australian National University in Canberra and her colleagues have shown the ozone hole is only part of the story. Global warming is just as important.

Warming powers winds

The team reconstructed Antarctic temperatures over the past 1,000 years, using an ice core from James Ross Island near the Antarctic Peninsula. The temperatures correlated with how strong and tight the winds are, so they could construct a record of wind strength.

They found that the current strength of the winds is unprecedented over the past millennium. But the surge in strength started in the 1940s, decades before the ozone hole.

So Abram's team simulated the last millennium using 8 climate models, driven by actual greenhouse gas levels previously reconstructed from ice cores. All the models predicted that the winds would pick up by the 1940s, suggesting greenhouse gases were playing a role. That may be because the Northern Hemisphere is warming faster than the south – because it has more continents – creating a strong temperature gradient that boosts the winds.

Such historical data is vital, says Wenju Cai from the CSIRO, Australia's national research agency, in Melbourne. In as-yet-unpublished work, he estimates that ozone depletion has caused two-thirds of the impact on the Antarctic winds, with greenhouse gases responsible for the rest.

Futureshock

If greenhouse gases really are contributing to the winds, it changes our expectations for what will happen to the climate in Australia and Antarctica.

The ozone hole is expected to heal in the coming decades, and if it was the only factor controlling the winds they would weaken and expand. So Australia would get its rain back, while the western parts of Antarctica might get some more protection against warming.

However, Abram says rising global temperatures will counteract this weakening effect on the winds. That means Western Australia will stay dry and the western parts of Antarctica, stranded outside the winds, will keep melting.

Cai estimates that, on our current emissions pathway, the two factors will counteract each other until 2045, so the winds will stay constant. After that, without reducing our emissions, greenhouse gases will boost the winds further.

Journal reference: Nature Climate Change, DOI: 10.1038/NCLIMATE2235

http://www.newscientist.com/article/dn25547-antarctic-wind-vortex-is-strongest-for-1000-years.html#.U4I2Y_ldXX4