Air Date: Week of April 10, 1998

Most of us associate increasing greenhouse gas emissions with climate change. But a group of scientists writing in the journal Nature say greenhouse gases are affecting the earth's protective stratospheric ozone layer as well. Lead author Drew Shindell (shin-DELL) is a scientist at the NASA Goddard Institute for Space Studies. He told Steve Curwood that thanks to rising emissions of carbon dioxide and other climate-changing gases, the ozone layer will stay depleted longer than previously anticipated.

Transcript

CURWOOD: Most of us associate increasing greenhouse gas emissions with climate change, but a group of scientists writing in the journal Nature say greenhouse gases are affecting the Earth's protective stratospheric ozone layer as well. Lead author Drew Shindell is a scientist at the NASA Goddard Institute for Space Studies. He says that thanks to rising emissions of carbon dioxide and other climate-changing gases, the ozone layer will stay depleted longer than previously anticipated.

SHINDELL: We expect that in the Antarctic, we will not see a great change. And that's mostly because the ozone depletion is already so thorough. In the Arctic, however, where the depletion hasn't been as great, we do see the ozone loss getting distinctly worse, and reaching its worst levels in about 15 years.

CURWOOD: Okay, we need some help with the science here. Why is this happening? How can greenhouse gases like carbon dioxide affect the ozone layer?

SHINDELL: Well, the chemistry that depletes ozone in the polar regions is extremely sensitive to temperature. It only happens in the polar regions because that's the only part of the stratosphere where it gets cold enough. So what the greenhouse gases do is warm the atmosphere down low near the Earth's surface, and that's what we commonly call global warming. But up high they lead to a cooling; it's the opposite effect. That makes the chlorine that's up there be more effective at depleting ozone.

CURWOOD: Now, your computer model predicts that greenhouse gases and climate change make ozone depletion worse. Is there an effect going the other way? Does ozone depletion make climate change worse?

SHINDELL: In general, the depletion of the ozone layer acts to reduce global warming, because ozone is itself a greenhouse gas. Now, in the future what we expect is that with the limitations on emissions of CFCs, the ozone layer should recover. And while that's certainly a good thing, since it will help to protect the Earth from receiving too much ultraviolet radiation, that should actually increase global warming slightly.

CURWOOD: In other words, once we started fooling with the system by adding chlorine that depletes ozone, by adding greenhouse gases, we've kind of gotten ourselves into something that it's pretty complicated to get out of, huh?

SHINDELL: Well, we've addressed the problem of ozone depletion to some extent. But the problem of ozone depletion has actually made the problem of global warming look not quite as bad as it might have looked otherwise. So once ozone depletion goes away, global warming begins to look as bad as it really is, and that's an issue where we have a long way to go before we've addressed that satisfactorily.

CURWOOD: What kind of basic conclusions can you make from your findings here about the whole scope, the whole effect of greenhouse gas emissions on the planet?

SHINDELL: Well, I would have to say that greenhouse gas emissions probably have lots of effects on the planet that we haven't even thought about. Maybe that's one of the most important lessons from this research: is that greenhouse gases don't just cause global warming, but it's an enormous change to the planet. And it has the potential to affect all sorts of things; it has the potential now, we see, to affect the ozone layer, which is not something that we had been thinking about before. Maybe it has the potential to affect lots of other things.

CURWOOD: Drew Shindell is an atmospheric scientist at the NASA Goddard Institute for Space Studies and Center for Climate Systems Research at Columbia University. Thanks for joining us today.

SHINDELL: Thank you.