00:00The Montreal Protocol was signed in 1987 to remove ozone-depleting gases from the atmosphere,
00:09but these gases have very long lifetimes of up to 100 years or more.
00:14So there's still plenty of them up in the stratosphere where they cause the ozone hole
00:19to form over Antarctica each spring.
00:23And while we are seeing the early signs of recovery, which is really great news, we still
00:29have to continue making sure that it is continuing to recover as expected, especially given new
00:37technological innovations that could potentially pose a threat to ozone recovery.
00:42Yeah, so what are those new threats that are compounding the problem?
00:47Yeah, there's a bunch of things going on, but they all have in common that they involve
00:55tiny particulates being injected into the stratosphere where they can speed up the
01:00rate of ozone depletion.
01:02So these might be things like rocket launches that emit reactive gases that can contribute
01:08to ozone depletion as they launch to space.
01:12They might include the wildfires, like the Australian bushfires of 2019-2020.
01:20Of course, they produced a lot of smoke.
01:22Some of that got into the stratosphere and we did observe extra ozone depletion that
01:27year.
01:28And unfortunately, with climate change, we do expect to see those mega wildfires becoming
01:33more frequent in future.
01:35And then there's things like these really controversial proposed solutions to climate
01:42change, such as stratospheric aerosol injection geoengineering, which would involve deliberately
01:48putting particulates into the stratosphere to stop some of the sunlight from reaching
01:54the Earth's surface and try and offset global warming.
01:57Unfortunately, that would probably cause some ozone loss and slow down the rate of ozone
02:02recovery.
02:03And so what do you think of that as a suggestion?
02:05I mean, it's very controversial and there are so many things that could go wrong.
02:12There's all the ethical questions, you know, who controls the thermostat, who decides when
02:15we stop doing it?
02:17And then there's the potential for things to go very, very wrong.
02:20So causing ozone depletion, potentially changing rainfall patterns and meaning that some areas
02:26get not enough rainfall and some places get flooding.
02:30So definitely in the climate change space, it's something that would need very careful
02:35thought and consideration before it's attempted at any large scale.
02:40So what's happened to the ozone hole in terms of its size over the years?
02:45Is it still decreasing?
02:49We have started to see the very early signs of recovery since about the mid 2010s, which
02:55is great news.
02:57There have been some unusual things going on in the last few years.
03:00So about the last four years or so, we've seen unusually long lived ozone holes that
03:06have lasted into the early summertime in Antarctica.
03:10Those are for different reasons relating to things like the Australian bushfires, kind
03:14of a series of one off events.
03:17But of course, climate change is bringing lots of surprises.
03:20So we don't know how that might play out in future.
03:22But I mean, those things aside, we generally expect that as these ozone destroying gases
03:27are eventually removed from the stratosphere, that we will see that ozone recovery happening
03:33later this century, hopefully.
03:35Why does the hole generally open up around this time of year and down this way?
03:41Yeah, it's a great question because most of the gases were emitted in the northern
03:45hemisphere.
03:46So why is it Antarctica that sees the ozone hole?
03:49That's because Antarctica is very, very cold.
03:53In wintertime, it's about the coldest place you can get on Earth.
03:57And that causes these clouds to form in the stratosphere called polar stratospheric clouds.
04:04They only form at very low temperatures.
04:06And they behave a bit like those solid particulates that we were talking about earlier, in that
04:11they act as surfaces that help catalyze the rates of chemical reactions.
04:17And they help a really big buildup of chlorine to occur in the stratosphere during wintertime.
04:24And then when the sunlight returns to Antarctica in late winter, early spring, that just kicks
04:31off this explosion of ozone-destroying reactions such that this hole appears over Antarctica.
04:38Yeah.
04:39And so that Montreal Protocol was so successful in cutting chlorofluorocarbons to address
04:44this issue.
04:46What's the danger if this continues to linger over the coming decades?
04:51So, as you said, the Montreal Protocol has been incredibly successful.
04:57If it hadn't been signed, we would have been looking at possibly a collapse of the global
05:02ozone layer by about the 2060s.
05:04But instead, we expect to see a recovery.
05:07We do still expect to see that coming.
05:09It's just a case of monitoring these new emerging issues, such as the wildfires, the rocket
05:16launches and so on, and making sure that those are not going to interfere with ozone recovery.
05:21Because we certainly wouldn't want to see ozone depletion happening outside Antarctica
05:26on any great scale, because, of course, it's a vital planetary boundary layer with protecting
05:31us from the sun's harmful rays and stopping us getting sunburned and skin cancers and so on.
05:39OK, Laura Revel, thanks so much for talking to us from Christchurch in New Zealand.
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