Hole in the Ozone May Have a Cooling Effect After All, Study Shows

Contrary to prevailing scientific beliefs, the hole found in the ozone layer may have a slight warming influence -- not because of its effect on temperatures, but due to its influence on wind.

Published in the journal Geophysical Research Letters, a new study suggests that the ozone hole is causing a shift in wind patterns that pushes clouds farther toward the South Pole. As this happens, the amount of radiation the clouds reflect is reduced, possibly causing a small amount of warming rather than cooling, as was previously believed.

"For some reason when you put an ozone hole in the Southern Hemisphere during springtime, you get this robust poleward shift in the [polar] jet stream during the following summer season," Kevin Grise, a climate scientist at Lamont-Doherty Earth Observatory of Columbia University, said in a press release. "People have been looking at this for 10 years and there's still no real answer of why this happens."

Curious to know if the ozone hole's impacts on the jet stream would have any indirect effects on the cloud cover, Grise and his team turned to computer models in order to determine how the clouds would react to changing winds.

In doing so, they found that the shifting jet stream carried with it high- and mid-level clouds along its journey toward the South Pole and the Antarctic continent. Meanwhile, the Southern Ocean experienced a drop in low-level cloud coverage. As a result, more radiation was able to make its way to the ground since the amount of energy clouds can reflect drops as they move poleward.

"If you shift the reflector poleward," Grise explained, "you've moved it somewhere there is less radiation coming in."

In 2007, the Intergovernmental Panel on Climate Change reported a direct cooling effect of some 0.05 watts per square meter's worth of energy reaching the ground as a result of a thinning ozone layer.

According to the new study, however, this slight change could be offset by as much as 0.2 watts per square meter due to shifting cloud coverage, particularly during the summer months.

However, what this means in real terms overall remains unclear.

"Theoretically this net radiation input into the system should give some sort of temperature increase, but it's unknown if that signal could be detected or what the magnitude of it would be," Grise said.

In comparison, the George Washington University Solar Institute has shown that an average of 175 watts per square meter reaches the ground from sunlight.

In the future, the researchers hypothesize that the jet stream will shift less during the summer months as the ozone layer above the South Pole recovers. Still, it's possible that rising levels of greenhouse gases could also play a role in shifting mid-latitude wind patterns and pushing the jet stream poleward.

"You have sort of this tug-of-war between the jet being pulled equator-ward during the summer because of the ozone recovery and the greenhouse gases pulling the jet further poleward," Grise said. "What the clouds do in that scenario is an open question."