Earth and Sky科普英語：Global Warming and Ozone 全球變暖和臭氧

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Could the coming century bring a new threat to the ozone layer? Discover one scientist's model of the effect of global warming and greenhouse gases on ozone -- on today's Earth and Sky.

DB: This is Earth and Sky.

JB: After 30 years of steady decline, Earth's ozone layer is thinner but seems to be stable. A ban on ozone-depleting CFCs is largely responsible. Computer modeling gives reason to hope for an almost full recovery of Earth's ozone layer within 60 years. But this sort of modeling is difficult -- and its predictions aren't iron-clad.

DB: And some models show the ozone layer could face a new threat -- from global warming. Drew Shindell, an atmospheric scientist at NASA's Goddard Institute for Space Studies in New York City, talked with us about his computer models of climate.

Drew Shindell: So we get this combination of temperature change and methane changes, water vapor changes, we have changes in reactive nitrogen species -- which come from another greenhouse gas -- and all of these things put together end up leading to a net decrease in the amount of ozone in the lower stratosphere.

JB: So if the world gets warmer, stratospheric ozone might be depleted again -- by 5 to 10 percent -- a return to today's low levels. What could be done then to protect the ozone layer?

Drew Shindell: Well, we would have to control greenhouse gas emissions and certainly that is a much more complicated problem -- and a much bigger change in economic systems and such -- than it was to change the CFCs.

DB: Special thanks today to NASA's Earth Science Enterprise. We're Block and Byrd for Earth and Sky.