IRA FLATOW: Now it’s time to play, Good Thing, Bad Thing. Because every story has a flip side. Now back in the 1980s, one of our planet’s pressing problems was the health of the ozone layer. It turned out that the chlorofluorocarbons, the CFCs, that we were working to that were working to destroy the ozone molecules in the Earth’s atmosphere, especially over the poles, well, they were doing a good job. So we had to find a way of not putting up more CFCs into the atmosphere.

Because the ozone plays a crucial role as sort of a planetary sunscreen helping to block UV radiation from the sun. So they came up with a global agreement that restricted the use of these CFC chemicals. And great, slowly the polar ozone hole began to repair itself. But now the repair doesn’t look so complete.

Jo Haigh is an atmospheric physicist and co-director of the Grantham Institute at Imperial College London. She and her colleagues discovered there is more to the hole story. Their work looking at the ozone layer over the entire planet was published in The Journal of the Atmospheric Chemistry and Physics this week. Welcome to the program, Dr. Haigh.

JOANNA HAIGH: Hi, [INAUDIBLE].

IRA FLATOW: So there’s good news and bad news about the ozone hole. Give us the good news first.

JOANNA HAIGH: Well the good news is that the international agreement, which was called the Montreal Protocol has been doing its job and the ozone hole over the Antarctic is gradually filling up. So each year it’s getting a little bit less severe. So that’s the good news. And the atmosphere’s responded as we expected when the chloroflurocarbons were banned.

IRA FLATOW: And now for the bad news.

JOANNA HAIGH: Well, the bad news is that what we’ve been doing is looking at ozone in other parts of the globe, so not in the high latitudes, not at the poles, but near the equator and in middle latitudes. And what we’ve found is that certainly in certain layers of the atmosphere, the lower stratosphere where most of the ozone is, it hasn’t recovered. In fact it’s continuing to decline, it’s going still going down, down. And so we’re not quite sure why that is.

IRA FLATOW: Is there any way to replace that ozone or is it filling up the void itself?

JOANNA HAIGH: It’s difficult to think about how you might replace it. We’ve got to think about why it’s going away, and if we can stop doing whatever we’re doing to make it go away. And we don’t really understand what that is. There’s two sort of ideas around this.

One is that it is actually to do with climate change. So I’ve been going on about CSEs and ozone, and of course the climate change thing is all to do with greenhouse gases, in particular carbon dioxide. And that’s, as we all know is warming the lower atmosphere. But in the stratosphere, it’s cooling it, and it’s also changing the circulation of the air.

So the air nat– [AUDIO OUT] latitudes, so there’s a big circulation. And we think that with climate change, that is getting stronger, that flow is going faster. And so the low ozone air is coming up and being transported from the equator to middle latitudes.

So that’s one explanation of why it might take place. But we haven’t actually proven that. The second idea is another chemical one and this has to do with things that are called very short lived substances. And they’re more things that contain chlorine and bromine and they come from various chemicals and paint strippers and things like that we’re using. And they are probably or possibly getting up there and destroying the ozone in these equatorial regions.

IRA FLATOW: Does that mean that the UV, the harmful UV radiation is affecting we who live on the surface of the Earth?

JOANNA HAIGH: Yes, so that’s the big question of course. In the Antarctic, the ozone depletion was very marked. But the sun’s not so intense there. If you go down to near the equator where we live around sort of 50 degrees north, then the radiation from the sun is much more intense.

And so if you weaken the ozone layer, then there’s scope for more effect from the sun, and in particular the UV is affecting DNA and anything that’s living and particularly especially white people who go around with not many clothes on, they’ll get more skin cancer.

IRA FLATOW: So this is something to watch for then.

JOANNA HAIGH: I think so. I mean at the moment, as I say, we haven’t really got an explanation. And we’ll carry on monitoring these measurements of ozone and see what happens. Perhaps it will just mend itself, which would be nice. But if it doesn’t, then we’ve got to try and think why it’s happening and try and stop it.

IRA FLATOW: We should be wearing our longer clothes then, during the summertime.

JOANNA HAIGH: That’s right. And hats.

IRA FLATOW: All right, Dr. Haigh. Thank you.

JOANNA HAIGH: OK. You’re very welcome.

IRA FLATOW: Jo Haigh is an atmospheric physicist and co-director of the Grantham Institute at Imperial College London.

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