by Kristen Minogue
Sep 29, 2009
The ozone hole above Antarctica could be posing another threat to the planet. The gap in the atmosphere not only ushers in cancer-inducing ultraviolet rays but may be accelerating global warming as well.
Scientists are just catching on to a shift in the winds that occurs at the ozone hole. The cooling of the stratosphere the hole causes intensifies the winds around Antarctica. The shift churns up ocean waters from the deep and could be releasing more carbon dioxide, the greenhouse gas responsible for a large part of global warming.
Normally the oceans act as a protective sink. Even with global warming, it is projected to absorb just under half of the carbon dioxide humans emit into the atmosphere. But the models that generate those numbers don’t take into account changes in the atmosphere – such as wind – that could make the ocean cough up more of its stored carbon dioxide. With warmer waters already giving off more carbon dioxide, the wind just adds to the load.
“The winds are shifting closer to Antarctica,” geochemist Bob Anderson said at the Comer Climate Change Conference in Wisconsin this fall. “There’s no question about that. The debate is centered on whether that shift in winds is having any impact on carbon dioxide being emitted from the ocean.”
Anderson, an adjunct professor of earth and environmental sciences at Columbia University’s Lamont-Doherty Earth Observatory, now believes wind could play a crucial role in climate change previously overlooked by most researchers, who have largely focused on the oceans.
He calls the process “wind-driven upwelling.” It works something like this: Winds driving from west to east push waters northward from the southern ocean around Antarctica. But they don’t all move north at the same speed. Some areas move faster than others. When that happens, nutrient-rich waters from the deep rise up to replace the missing surface waters. And when they do, they bring their sunlight-trapping, planet-warming carbon dioxide with them.
Anderson developed the idea after noting large spikes in opal – the silicon-rich stone more commonly seen in jewelry stores – during the warming period that melted the glaciers 17,000 years ago. He found the opal in fossilized sea shells mixed in the sediment cores taken from the ocean floor, cores that store a record of past epochs.
His findings, published in the journal Science this year as well, suggest the opal could only have come from deep-ocean upwelling, providing the silicon needed for diatoms (microscopic algae) to make the opal found in their shells. The same process would have brought more carbon dioxide to the surface as well, Anderson said. The opal became a “proxy” for detecting the ancient release of carbon dioxide.
“It seemed to me in looking at our results from the southern ocean that you could drive upwelling by increasing the winds, because it’s the winds that drive upwelling today,” Anderson said. “So, if you turn up the winds in the southern ocean, you can increase upwelling.”
His findings are arousing lots of debate.
Up until now, most climate change scientists have relied on ocean currents to help explain global warming. According to this model, the Atlantic Ocean works like a multilayered transport system. Hot water from the tropics flows to the poles, where it cools, gets heavier, sinks and then flows back down to the equator. This conveyor keeps the mid-latitude regions such as the United States and Europe from getting too cold – unless an influx of cold freshwater from melting glaciers shuts it down.
Wally Broecker, who originally developed the ocean conveyor-belt model of the circulatory system that keeps much of the earth habitable, is a little skeptical of giving winds too prominent a role in the conversation. Broecker, also at the Lamont-Doherty Earth Observatory, is one of the pioneers of contemporary climate science and coined the phrase “global warming.”
“There are big changes in the ocean that penetrate all of the South Atlantic, and I don’t think we know enough about ocean circulation to say that those couldn’t have done the job,” he said at the Comer Conference in response to Anderson’s presentation.
But researchers cannot deny that the winds have shifted. Scientists discovered years ago that, when ice breaks up in the Arctic, the area near the equator where the north and south trade winds merge, moves south. Anderson said this could lead to a complete reorganization of the winds in the Southern Hemisphere, increasing the release of carbon dioxide.
The Northern Hemisphere may not be able to take all the credit for the shift, though. Anderson is among the scientists starting to suspect the ozone hole might be driving a change in the winds as well.
United Kingdom scientist Corinne Le Quere helped ignite the debate in 2007. She and a team of researchers noticed that instead of absorbing more carbon dioxide – which the ocean should do in response to rising levels of the gas in the atmosphere – it was absorbing less.
At the end of a paper she published in Science, Le Quere speculated that the depleted ozone layer could have caused the southern winds to shift. Anderson’s more recent research supports this, but the idea remains an issue of contention for climate change scientists.
In the debate over water and wind, Anderson said he did not think accepting the role of the wind meant discarding the impact of the oceans. To him, it’s just one more piece in a complex and interconnected puzzle of the Earth.
“The winds affect the oceans affect the ice affect the winds. And it’s really hard to pull apart the chicken from the egg.”