Earth and Sky【5】

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.