This TED Talk features climate scientist Sean Davis, recorded live at TEDx Boulder, 2017.

So I'm a climate scientist, and if this room is representative of the country we live in,

that means about 60% of you, so maybe from about

thereover, don't strongly trust me for information on the causes of climate change.

Now, I promise to tell the truth tonight, but just to humor that demographic, I've started

this talk with a falsehood. This statement was not made by President

Obama. It was actually made by President Reagan. And it wasn't about climate change and the Paris

Climate Accord. It was actually about the Montreal Protocol and stratospheric ozone depletion.

Now, I'm sure that many of you aren't familiar with this environmental problem,

but you should be, because it's a rare environmental success story.

And it's worth revisiting, because sometimes we need to examine the world we've avoided

in order to find guidance for the choices we make today.

So let's go back to the 1970s when some questionable choices were made.

First of all, whew, hairstyles.

Second of all, objectively terrible quantities of hairspray. And third, CFCs, chloroflorocarbons, man-made chemicals that were used as propellant in aerosol spray cans.

And you see, it turns out, these CFCs were a problem because they were destroying the ozone layer.

Now, I'm sure most of you have heard of the ozone layer, but why does it matter?

Well, quite simply, the ozone layer is Earth's sunscreen, and it's really fragile.

If you could take all of the ozone, which is mostly about 10 to 20 miles up above our heads,

and compress it down to the surface of the earth, it would form a thin shell only about two

pennies thick, about an eighth of an inch. And that thin shell does an amazing amount of work,

though. It filters out more than 90% of the harmful UV radiation coming from the sun.

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