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[chimes] 

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[chimes fade out] [concerned driving music starts] 

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[music fades out] >>Paul: I'm going to tell

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a real scientific and I think public policy success story,

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and it's about the ozone layer. You can see the globe

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here. We divide the atmosphere into a variety of layers.

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The troposphere is the lowest layer, it's where all of our weather occurs.

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The stratosphere is the next layer up, and that's what I'm going to really focus on, because that's

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where most of our atmospheric ozone is located.

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Now ozone is critical in our atmosphere because it screens ultraviolet radiation.

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Ultraviolet radiation, these are energetic solar

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photons, there are, they are strong enough

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to break the bonds of biologically active molecules, like DNA

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for example. So, if you decrease the amount of ozone,

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which is screening this UV radiation,

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you get more at the surface, and what that'll do is that you get,

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you sunburn a little more quickly. For example a person like me,

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I'm out for about 15 minutes and I'll get a sunburn. But it does a lot of other things.

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It impacts crops, it can cause cataracts. There's a famous study

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of water men out here on the Chesapeake Bay in which they found

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that their amount of time on the bay was proportional

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to the cataracts that they got. The longer you were out there, the more cataracts you got.

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But that's extended exposure over the years. So ozone is really

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a critical gas in our atmosphere.

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In 1974, these two gentleman on the right, this is 

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Sherry Rowland, and this is Mario Molina. They proposed that there were

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a class of gases being emitted into our atmosphere that

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could destroy the ozone layer. These are chlorofluorocarbons, or CFCs.

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So, they proposed this, and it was

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quite controversial at the time. They took a lot of heat 

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because this chlorofluorocarbon industry, chemical industry,

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was used in a variety of different kinds of products.

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You can see some of these, many of us remember, it used to be used as a propellant

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for hairspray, and deodorants. It was

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used to make foam products, like these cups you would get

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from McDonalds or other companies. It was used,

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CFCs were used in air conditioning and in car air conditioners.

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It was also, there's another kind of gas called a halon.

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Halons are used in fire extinguishers, they contain bromine. They can also

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destroy ozone. So this is proposed in 1974,

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and there was a huge amount of energy and effort that was going in

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the late 70s and early 80s to see what the impact

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is on ozone, to measure ozone and these gases in particular.

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Now, in 1985, there was a publication

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of a paper on ozone down over Antarctica.

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And these three gentleman here, this is Joe Farman,

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Brian Gardiner, and John Shanklin. They're standing in

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front of an instrument that measures the total amount of ozone between the surface and space.

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And they published their data. And you can see it here,

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this is a measurement, this is the total amount of ozone between

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the surface and space over the station. It's Halley Station down in Antarctica.

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And what that shows is that the level of ozone

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was dropping and it was dropping really fast. Okay. 

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It was an amazing study that they published, and the quality of these 

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data are such that there was no dispute to this. Ozone 

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was going down, and it was going down fast. This was a real shock

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to the atmospheric community, when this paper was published.

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Shortly thereafter, and this was in the,

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in 1985 also, a scientist at the NASA Goddard

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Space Flight Center P.K. Bhartia made an image

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of what this ozone looked like over Antarctica.

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And so you can see Antarctica here in the center, South America, Africa,

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Australia, and here in the middle is this very low ozone area,

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these red colors and yellows that you see here indicate very low ozone.

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And it was dubbed "the Antarctic ozone hole".

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So ozone was going down fast, and it was a huge region. 

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This is a very large region, comparable to, this continent of

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Antarctica is a large area, so there's a large depletion over

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a large area. And we didn't actually understand what was going on at the time.

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But within a couple of years, we figured out it was actually due to these

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chlorofluorocarbons and halons.

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So there was a lot of consternation about this. What are we going to do? How can we

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stop it? What are other measurements can we make? So the rising 

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concern about the problem amongst the nations of the world,

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there was already discussion about, should we get together and create an agreement?

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And in fact after a couple years, they did create an agreement.

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This is an agreement called

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the Montreal Protocol. 

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These are, this is a, this shows a meeting of the parties to the Montreal Protocol.

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took place in Doha, in the Saudi Arabia peninsula

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And here you can see the Montreal Protocol had a series of

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agreements the initial one, and they were added on to, further

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strengthening regulations of these chlorofluorocarbons. So eventually,

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the production of chlorofluorocarbons and halons

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was fully agreed to. Now, you can see the nations of the world, 

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there are little signs here. Here you can see, this is me sitting

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way in the back of this meeting. Even though

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the scientists, we bring them all the information, we're always put at the back of

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the meeting. When they need us, they'll call on us, but we sit in the back and listen

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 to all the discussions. And mostly these discussions are about countries'

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ability to maybe use a CFC for a short time. There are a lot of different

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things going on in these meetings.

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Okay. So now what's happened with ozone. Well first of all

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let me talk about chlorine. So chlorine,

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it was going up and up and up through the 1960s, 1970s, 1980s.

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These are a combination of all the CFCs and halons. And then the

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Montreal Protocol was signed here in 1987, and

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slowly those regulations began to take hold, and in fact

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the projection is that these

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ozone-depleting substances are going to decline with time. Now this is going to take a long time,

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because CFCs, these chlorofluorocarbons have long lifetimes. 

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For example, CFC 11 has a lifetime of about

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52 years. CFC 12, which was used in

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your car air conditioners, has a lifetime of over 100 years.

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So it's going to take a long time, even though the production and emission

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of these gases has been regulated, it's going to take a long time for them

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to come out of our atmosphere.

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So what's happening with ozone now? So this is showing

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this is in percentage, the change of ozone over time in percentage.

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You can see the observations as you go into the 80s. You can see

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that ozone was going down, the CFCs were increasing,

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the Montreal Protocol is signed here. Pretty soon the chlorine 

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has started to decrease, and you can almost,

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there's a Mt. Pinatubo effect right here, but you can almost see that ozone isn't going

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down anymore, and maybe there's a hint that things are starting to go

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up. We can't say that, as scientists we can't that's true yet, 

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but I think we're getting to the point, within the next few years, I think we'll actually 

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be able to say statistically that ozone is increasing 

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in our atmosphere. Let's keep our fingers crossed. 

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Now, the other way of looking at this is we can use a model 

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to take a look at what would have happened to ozone if we'd done nothing.

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So I'm going to show you a little model study here. And on the top left, I'm going to show you

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the expected world. And this is with the Montreal Protocol,

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CFCs are going to decline. Over here is what we call "the world avoided".

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And this is chlorine going up. If you look on the picture,

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you can see the amount of chlorine in the expected world and the amount of chlorine

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in the world avoided. So you can see here it's 4.5, there it's

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already a little bit higher because of the Montreal Protocol,

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this is because of the Montreal Protocol, that's without one. And you can see this flying by 

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fairly quickly, as you can see the date on the right, you can see the ozone hole appearing

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every year. Chlorine continues to go up in this

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world avoided, and now you can actually see it peaked down at about 4

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and it's in a slow decline as we're out to 2022, 24.

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If you look here at this world avoided you can now start seeing a little ozone 

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hole deep low values appearing over the Arctic. 

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And you see the very very large ozone loss 

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in over the Antarctic region. If you look at the expected world,

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you don't see any of those things. And in fact this chlorine continues to increase,

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you can see ozone going down now in the tropics 

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and in the subtropics. So you can see that here you're dominated by reds and

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oranges, the higher ozone levels. In the world avoided, you can see

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that ozone is declining and declining and declining. 

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Now, this is about 40 to 50 times, by the time you get

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out to 2065 here, this 40 to 50 times

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the natural level of chlorine in our atmosphere. Chlorine and bromine

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combined. And this has gone down, it about needs to go down to

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about 1.2, this is about halfway there. But you can see

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the difference in ozone. 65 per-, or excuse me, about two 

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thirds of the ozone layer is destroyed if there had been no 

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Montreal Protocol, if nothing had been done. Okay. Now what does that mean? 

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That means huge impacts on crops. 

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For somebody like me, I mentioned that if I go outside, 15 minutes I'll get a

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perceptible burn. In that world it's 5 minutes. Okay.

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So you go out and you walk for a quarter of a mile, you would get

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a perceptible sunburn. So, this is an 

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incredibly bad world, we don't want to live in that world. This is the one that

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we expect. Now, we can do, 

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as I've already shown, we can do these projections of where ozone is going.

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Here we can see the observations, this shows a model projection, 

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and now I put two model projections on here. The lower one is

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 a world in which both ozone-depleting substances,

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it has a Montreal Protocol in it, they've been regulated and so ozone is

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going up. But in one, greenhouse gases are regulated.

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In the other, greenhouses gases continue to go up.

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And in fact, ozone continues to go up. So,

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the net impact of increasing greenhouse gases is that the ozone layer begins to pile

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up lots of ozone. So instead of a depleted ozone world, we're going

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to go to an ozone world where there's probably too much ozone.

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Now what does that mean for the environment? I actually don't know. I don't think we 

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know as scientists what's going to happen there.

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So let me say another word about

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what happened. This is, I love this picture,

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I owned a 1967 Ford mustang fastback. It was

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a hot car. I love this car. It has a CFC air conditioner in it.

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So I was using CFC-12 in that

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particular air conditioner. Here is a Tesla, a modern Tesla.

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It uses a replacement compound called an HFC,

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in fact HFC-134a. And in fact in all your cars right now, 

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you have that particular refrigerant in your

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car air conditioner. So this is the compound that replaced the CFCs. 

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Now the beauty of this is this is a hydrogen, a fluorine, and a carbon.

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It doesn't have chlorine, so it doesn't destroy the ozone layer. 

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The problem with HFCs though is they're greenhouse gases.

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The particular HFC 134a is about, 

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pound for pound, it's about 14 hundred times more

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efficient at warming than CO2.

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So you could take one pound of this HFC-134a,

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is equivalent to about 14 hundred pounds of CO2.

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So the replacement compounds for the CFCs

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are greenhouse gases. And the question is, what are we going

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to actually do about these? Now this shows a particular HFC, this is HFC-23.

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You can see these are observations they're increasing with time. Because we

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replaced the CFCs. There are many other HFCs.

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This is the one I talked about, it's in your car air conditioner, 134a.

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This one 32 and 125, these are probably

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in your home air conditioning units. So all these HFCs

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are increasing with time, and these HFCs are all

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powerful greenhouse gases. So, we solved the problem, 

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that is the problem of ozone depletion, but in fact, and in fact those

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CFCs were also powerful greenhouse gases, but we replaced them with compounds 

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that are also powerful greenhouse gases. 

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So you could do a lot for climate if you figured out how

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to take these compounds and replace them with compounds that are both

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friendly to the ozone layer and friendly to climate. And in fact

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there are technological solutions. So that goes back to the Montreal Protocol.

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The Montreal Protocol could in fact take action on these

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HFCs. We don't know that that's going to happen, but it might.

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So let me kind of summarize

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where we've been. So I told you a good story. We got rid of these

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CFCs, they're now regulated, they still exist in various places around the atmosphere,

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but they're slowly declining. That's a great story. In fact, the outcome

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of that would have been an environmental disaster

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if they had kept growing. We used a lot of satellite information

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to take a look at the ozone problem. Most of the observations

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you've seen on this presentation have come from NASA

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satellites, including the Aura satellite that you can see here. 

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Now what does the future hold? Well, the future's in our own hands.

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We have two things we can, you can regulate these compounds,

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and that may happen. But the one thing that we really need to do

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is we need to continue to look at the atmosphere continue to make measurements

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of what's happening to our atmosphere. And that's where satellites like Aura

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and its follow-ons are crucial to knowing where we're going to be in the future. 

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Thank you. [applause]

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[applause dies out] 

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[whoosh] [beep beep... beep beep...] 

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[beep beep... beep beep... beep beep...] 

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[end]