NASA Sees Definitive Evidence of the Montreal Protocol’s Success

The Montreal Protocol has been a great success at banning the production of ozone-depleting substances. And we know this because we’ve been measuring those substances at the Earth’s surface since the 1980s or even before, in some cases. So before the Montreal Protocol, ozone-depleting substances at the surface were going up rapidly. Once the Protocol was signed and the regulations went into effect, we saw at the surface, levels of ozone-depleting substances going down. And so that’s great. But those substances have to get high up into the stratosphere before they can destroy ozone, and they have to break down high up in the stratosphere, and the chlorine that gets released from the chlorofluorocarbons that’s what actually destroys ozone. What we haven’t had up until now is any measurement inside the Antarctic ozone hole that the chlorine levels there is actually going down. What I’ve shown is that if you’re very careful about when you measure hydrogen chloride, that’s HCl, in the atmosphere, and you measure it over time, you can see that HCl, so that reactive chlorine that destroys ozone, those levels are actually going down inside the Antarctic ozone hole. So that’s great, so that’s part of saying, “Hey, the ozone hole’s recovering, it’s getting smaller and it’s because of declining chlorine.” But the other part is to also look at how much ozone depletion is going on at the same time, because ozone levels can vary for a lot of different reasons, mostly because of temperature. If one year it’s warm, you don’t have as much ozone depletion. One year’s really cold, you have more ozone depletion. So it makes it really hard to see the signal that the atmosphere’s showing us, is the ozone hole really recovering? So what we did in this study, we were able to look at ozone changes during a period of time, in the winter, when most of that ozone change is coming just from chemical changes, so that temperatures aren’t really affecting it very much. And we’re able to do this because of measurements from the NASA Aura instrument called the Microwave Limb Sounder, so what we’ve seen by using the MLS data is that ozone depletion has declined. It does vary a lot still, but it declines and it’s declining sort of in step with the chlorine changes, and so that’s what we’re excited about, is that we see, for the first time, chlorine levels are definitely going down, and ozone levels are responding to it.

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