You're listening to Shortwave from NPR.

Hello there, Rebecca Hersher.

Hey, so what do you got for us today?

My dear climate correspondent.

Oh, I have a twisted tail of math, ethics, and climate change.

Are you interested?

Yes, I love a twisted tail.

I know you do, I know you do.

Okay, so this story is about the most important tool that the environmental protection agency has

for cracking down on greenhouse gas emissions, like reducing emissions from coal-fired power plants

or making the exhaust that comes out of your car's tailpipe cleaner.

And that tool, it is a single number.

A single number, a digit, like four?

Four, that is a number, or more like four dollars.

This number is expressed in dollars.

It's called the social cost of carbon.

And it represents all the cost of humanity of emitting one ton of carbon dioxide into

the atmosphere.

For example, the cost of lost crops and flooded homes and lost wages when people can't

safely work outside, plus the cost of climate-related deaths.

Okay, so I want to get this straight.

The EPA estimates the value in dollars of all of the bad things that happen because

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