Climate Change and Ozone: Laws of Unintended Consequences

When it comes to averting dangerous climate change, an awful lot of people seem to hold out hope that we can blast our way out of the mess we’re in. Nothing so boring as energy conservation, or even replacing coal, oil and natural gas with solar, wind and nuclear: Instead, let’s shoot sulfate particles into the atmosphere to reflect away sunlight! Let’s load up the oceans with iron so plankton will grow like dandelions on my lawn and suck up the heat-trapping carbon dioxide produced when we burn fossil fuels!

Hope springs eternal. This week brought a conference on weather modification, with the emphasis on getting clouds to drop their raindrops. My favorite paper was, alas, withdrawn: it proposed a machine—a ship, actually, with “four torpedo-shaped hulls”—that would “stop hurricanes from wrecking large parts of America.”

While the inventor goes back to the drawing board on that one, a new study suggests that geo-engineering proposals may well blow up in our faces. Injecting sulfate particles into the stratosphere would shred Earth’s protective ozone layer, conclude scientists led by Simone Tilmes of the National Center for Atmospheric Research, delaying the recovery of the Antarctic ozone hole by decades and triggering serious ozone loss over the arctic.

The problem, as she and colleagues explain in a paper published online in Science Express, is that although sulfur particles from volcanic eruptions do cool the planet’s surface, they also provide a surface on which chlorine gases—the chief culprits in ozone depletion—can cause chemical reactions that speed the destruction of ozone molecules. Sulfates themselves do not destroy ozone; they simply provide a convenient surface for chlorine to do so.

“Trying to artificially cool off the planet could have perilous side effects,” Tilmes said in a statement. “While climate change is a major threat, more research is required before society attempts global geoengineering solutions.”

Over the next few decades, the quantity of sulfates that geo-engineering schemes envision could destroy one-fourth to three-fourths of the ozone layer above the arctic, she calculates. Because of atmospheric mixing, this low-ozone mass would sometimes swing over inhabited regions of the northern hemisphere, leaving people and other living things without the protection from ultraviolet light that ozone provides. Injected sulfates would also postpone by 30 to 70 years the repair of the ozone hole over Antarctica, or until at least the 2090s.

More UV raises the risk of skin cancers, including deadly melanomas, and decimation of phytoplankton that anchor marine food chains. But hey, what’s a little (or a lot of) melanoma and fisheries crashes if we can avoid the hard steps needed to avert dangerous global warming?

In one of those “you can’t win for losing” things, another study concludes that if the ozone hole over Antarctica does return, as it is expected to now that the world has banned most ozone-destroying chemicals (and assuming we don’t mess it up with geo-engineering), the antarctic will finally start warming the way the rest of the world has.

It’s been a puzzle of climate-change models that the interior of Antarctica has not warmed as much as models project. Average global surface temperatures have been increasing, but the interior of the southern continent has actually been cooling during the austral summer and fall. That’s been traced to ozone depletion which, through a complicated mechanism, produces atmospheric circulation patterns—basically, intense westerly winds—that block warm air masses to the north from reaching Antarctica. In addition, with low levels of ozone the lower stratosphere over Antarctica doesn’t absorb as much ultraviolet radiation.

Once the ozone returns, calculate Judith Perlwitz of the University of Colorado at Boulder and colleagues, the warming trend will kick in as the westerlies fade and UV absorption causes air temperatures 6 to 12 miles up to rise by as much as 16 degrees F.

That might be good news for travelers who are waiting for Antarctica to warm up before they book a trip to the south pole, but it will be bad news to climate-change deniers. They have long pointed to Antarctica's cooling to question the basic predictions of global warming.

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