Michael Greenstone

And they said, okay, if you live north of that line where it's colder, we're going to install central heating systems and we're going to give you free coal.

So that's in the north.

In the south, the policy was, guys, you're out of luck.

No heating.

Migration was greatly limited.

And I thought, wow, this is the thing I've been searching for.

If you were born just to the north of the river, those people, they were the intended beneficiary of this policy.

On average, they're living about three years less than people born just to the south.

And that was such a striking finding, at least to me, that I thought, wow, I hadn't realized quite how devastating air pollution was, even though I've been working on it.

children born just to the north of the Hawaii River completed almost one full year less of education than kids born just to the south.

And not just that, we're able to observe them as adults.

And on average, they earned about 13% less than children born just to the south.

I think this is the first large-scale evidence on the impacts of long-run early childhood exposure at the levels of concentrations that prevail in many parts of Asia and sub-Saharan Africa.

We have probably been understating the losses from air pollution by about 50%.

But then some kind of good news.

That would imply that the benefits of reducing air pollution are 50% larger than we realize and would justify more stringent environmental regulations.

And if you take my estimates literally, they imply that a child born in 2018 relative to a child born in 2013 will live 1.4 years longer.

The United States accomplished nothing like that so quickly after the Clean Air Act.

The Clean Air Act was really focused on reducing pollution locally in parts of the country where pollution concentrations are very high.

CO2 is a totally different ball of wax in the sense that it is a global pollutant.