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Chapter 1: How does air pollution affect cognitive abilities?
Hey there, it's Stephen Dubner. We recently got an email from a listener who wondered if the recent wildfires in the Southeastern United States were going to affect the final exam scores for high school and college students. Not because students were displaced by the fires, but because the wildfire smoke might have affected their brains.
This listener had apparently heard an episode we made a few years ago called This Is Your Brain on Pollution. So we've decided to replay that episode for you today with updated facts and figures. As for whether this year's test scores in the Southeast were affected, that sounds like an excellent research question for an enterprising investigator.
If anyone out there decides to do that research, let us know. We're at radio at Freakonomics.com. As always, thanks for listening.
It's worse than cigarette smoking. It's worse than wars. It's worse than auto accidents.
Wow. What's worse than wars and car crashes and smoking? Here, I'll give you a hint. Imagine you were getting ready to leave your house for work or school, maybe to go for a run. There is some standard information that most of us seek out before leaving home. There's this.
We've got partly sunny skies. It's 85. South winds at 14.
And there's this. We've got multiple accidents, stalled vehicles causing major delays. It makes sense to check the weather and traffic before leaving home, but there's information we don't usually check that could be just as important, if not more so. What if this is what you heard in the morning?
The level of particulate matter in the air today is above the recommended World Health Organization guidelines.
Or even this.
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Chapter 2: What evidence links air pollution to student performance?
Accordingly, our concern about pollution has been falling. In 1990, 58% of Americans said they had a great deal of concern about air pollution. Today, that number is only 40%. Here is one of those 40%.
I think air pollution is the greatest single threat to human health on the planet.
Michael Greenstone is an economist at the University of Chicago, where he directs the Energy Policy Institute and co-directs the Climate Impact Lab. He also spent a year in the Obama White House working on climate policy. One of his creations is called the Air Quality Life Index.
The Air Quality Life Index uses satellite data to say how much longer would people in any part of the world live if their area was brought into compliance for what air pollution should be.
So how does air pollution affect life expectancy?
The average person on the planet is living 2.2 years less than if where they lived complied with WHO standards. Which is what leads Greenstone to say this. It's worse than cigarette smoking. It's worse than wars. It's worse than auto accidents.
The World Health Organization estimates that roughly 7 million people die every year from exposure to fine particles in polluted air. That's at least double the number of people who died globally from COVID in 2020 and more than five times the number of people killed every year in car crashes. The more proximate causes of the pollution deaths include pneumonia, stroke, and heart disease.
The economic costs of pollution are also massive. One estimate puts it as high as $6 trillion a year, or about 5% of global GDP. Here again is Andrea Linneaus.
The interest in economics is fundamentally about the productivity impacts. And so part of the reason we're interested in cognition is that if cognition affects productivity, then the costs of exposure to air pollution may be much, much larger than we had previously estimated.
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Chapter 3: How does particulate matter impact life expectancy?
The UK burned so much coal that the natural ecosystem adjusted.
There's a story of microevolutionary biology, which is about the peppered moth. I'm not sure if you've ever heard about this.
That is Stefan Hiblich, a German economist who teaches at the University of Toronto. As for the peppered moth...
The peppered moth appears in the UK in two varieties, a darker and lighter variety. And it's well known that before industrialization in the north of England, the lighter variety was the predominant species. And this was basically because it could hide on trees from predators.
But then as cold smoke started turning trees darker, we see a rise in the instance of this darker version of the peppered moth.
So the darker version of the peppered moth was a byproduct of heavy air pollution, kind of like those white shirts worn by office workers in Gary, Indiana. For Hiblick and his fellow researchers, the moth would be a useful indicator in a much larger story about pollution. It's a story that involves geography, poverty, And wind, a westerly wind, to be precise.
In cities in the Western Hemisphere, winds blow from the west to the east. And you might observe that in a lot of these cities, east sides are more deprived.
Deprived, meaning lower income. There are, of course, exceptions, but the general rule is that the east side of many cities in the Western Hemisphere are poorer than the west side.
We started wondering if this was driven by coal smoke during industrialization and a sorting of poor people into the East Side and rich people away from the East Side. And we wanted to understand if this has long-lasting effects.
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Chapter 4: What role does the Clean Air Act play in pollution control?
What we're seeing is that really polluted and really unpolluted neighborhoods, they are basically becoming even more extreme, either richer or poorer. What we're finding is that one standard deviation increase in pollution would lead in the past to about 15% pollution. higher share of low-skilled workers in neighborhoods, and then today we would see that this would go up to 20%.
The likely explanation is a classic case of path dependence. You have the causes initially that the east side had these negative effects of pollution. Poor people sorted there, and then the effects were cemented over time by additional investments, right? Maybe you had a highway cutting off the east side from the west side, or you have poorer building structure.
As a result of that, you have a certain composition of residents. You have less funding for schools. You have less funding for other amenities. And this is then the snowball effect. In our paper, we find, for instance, that test scores in these east sides are lower and that crime instances are higher.
OK, lower test scores and higher crime in the areas that have historically had high pollution. But again, how can you untangle cause from effect? Does pollution itself lower people's cognitive abilities or do people with lower cognitive abilities sort into polluted areas? Lower cognitive abilities may mean lower incomes, which may mean fewer options when it comes to where you live.
And how can you untangle this question in the face of snowball effects like school funding? This brings us back to Andrea Linneaus.
I had been reading the literature on the effects of air pollution on productivity, but also other behaviors, for example, crime. And knowing that a leading hypothesis for those effects was really this cognitive impact that So there's a literature showing that the test scores of high school students is negatively impacted by exposure to particulate matter.
But we didn't at that stage have much evidence for the cognitive effects in adults. And that makes sense because we don't regularly sit high school exams every year as adults.
There was one piece of evidence for the cognitive effects of pollution on adults. It came from a paper that analyzed baseball umpires.
Yeah, who said economics isn't fun?
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Chapter 5: How do historical pollution levels affect modern demographics?
It certainly has a great quantity of smoke hanging over it. Like Gary, Indiana, Pittsburgh was a two shirt town, and it's still rated as the 16th worst U.S. metro area for particle pollution. That said, not all parts of the Pittsburgh area have the same level of pollution on a given day. And the same goes for all the places that Severnini and Linneaus wanted to measure in their study.
Pollution levels are not measured around us, like attached to our bodies. So that would be the ideal experiment. You are breathing the air, you know exactly how much pollution you have in that air. It's not the case. And so that creates noise in the data, which would underestimate the relationship between cognitive function and pollution.
but they did find a way to address that problem.
We used the wind direction that brings pollution from other locations, and that makes a uniform level of pollution for all individuals in an area, independently on whether they are close or slightly farther away from the monitor.
Severnini and Linos ran their analysis across more than 4 million Lumosity gameplay observations and measured that against pollution data across the U.S. What'd they find?
The headline result is that there is a cognitive impact for the working age population.
In other words, it's not just among test-taking students.
We're actually finding that the largest effects are for people under 50.
and not just for baseball umpires either.
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Chapter 6: What are the cognitive impacts of air pollution on adults?
I was going to complain about the time of day, but then again, it's more or less the same time of day for all of us.
Yeah, we should say it is late in the day. It's a little after 5 p.m. on the East Coast and Levitt's in Chicago. So that's still end of the day.
So he's got a one hour advantage on this.
Can I say my air conditioning is broken and it's really hot?
Oh, OK, you win then.
In case you don't know, Steve Levitt is a professor emeritus of economics at the University of Chicago. He's also my Freakonomics co-author, and he hosts a few episodes of this show as well. Angela Duckworth is a psychologist at the University of Pennsylvania in Philadelphia. She's the author of the book Grit, and she and I used to host the No Stupid Questions podcast together.
Anyway, the three of us set out to play three games as part of Lumosity's fit test. One game is said to measure mental flexibility. Another, memory. And the third, called Train of Thought, purported to test our attention by having us guide different colored trains to their respectively colored destinations. If all that sounds super easy, well, you should try it. Okay, here we go.
this is so cute i love trains oh my god this is hard it's one of the hardest things i've ever done in my life oh my god let's see i got 13 500 points and i scored better than 70 i don't even want to tell you guys how i did come on tell me how you did
I was 34 out of 39. 97%. Wow, Levitt. I just said it was the hardest thing I'd ever done. I didn't say I was messing up.
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Chapter 7: How significant is the economic cost of air pollution?
So I can't say I've heard many more theories that would surprise me more if they were true. But what do I know about the world?
So let me read you some numbers. This paper finds negative cognitive effects at just 20 micrograms per cubic meter. Now, here's what's interesting. In the three cities where we are, I'm in New York, Angela's in Philadelphia, Levitt's in Chicago. On average, in 2019, for instance, New York was the lowest of those three. It's seven micrograms per cubic meter.
Philly is at 10.3, and Chicago was the worst at 12.8. How many particulates are there in Chicago today? Okay, so I have some good news and some bad news. The good news is, Levitt, you are suffering very low particulate matter in Chicago today. As of today, Chicago only had 8.7 micrograms per cubic meter. Philadelphia and New York, we have very high levels today, as it turns out. Do we?
Yeah, 23.4 in New York and 24.6 in Philadelphia. Is there that much variation in particulate matter? There is that much variation, not only place to place, but day to day.
Wow. That's what's really interesting, the day to day part. I didn't realize that.
Levitt, earlier you said that you just felt incredibly sharp and focused when it came time to do the tasks. Do you think that had anything to do with the relatively low level of particulate matter in the air in Chicago?
I wouldn't think so, but maybe I should start tracking it. I could, without knowledge of the particulates, read how I felt each day.
So you each sound relatively skeptical of the findings of this paper. Let me just ask for like a confidence level, zero to 10, let's say, that these findings are somewhere in the ballpark of useful and true.
I want to rate my own confidence in saying anything about somebody's findings before reading their paper. I would say that would be like a one.
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Chapter 8: What future policies could improve air quality and cognitive health?
Long run meaning is a little bit hard to suss out. The more challenging thing is, you know, to find instances where there's long run variation. I think in both the health and in the cognition literatures, The holy grail is not to rely on studies that use either day to day or month to month, but to find a setting where there's like a permanent difference in air pollution.
It's much harder to come up with those examples, but that is after all what policy is trying to do. It's not trying to reduce pollution on Tuesday. It's trying to reduce pollution 365 days a year. Greenstone thinks he may have found the Holy Grail. About seven or eight years ago, I stumbled upon an example from China that seemed to mimic this kind of ideal.
And that's something called the Huai River Winter Heating Policy. It dates back to when China was much less wealthy, and there just weren't enough resources to provide winter heating for everybody. So they did something quite arbitrary and capricious. They drew a line across the middle of the country, and that line follows the Huai River.
The Huai River, by the way, runs west-east, not north-south.
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.
So what Greenstone was looking at had nothing to do with whether people sorted themselves into neighborhoods on the east or west side of a city, like Stefan Hiddlick looked at in England.
This had to do with comparing the health and educational outcomes of people living on the north side of the river, where people were warmer in the winter but exposed to a lot of coal smoke, and the south side, where you might have been colder but didn't have much coal smoke. And thanks to Chinese government policy, there was almost no migration from one side of the river to the other.
Migration was greatly limited. And I thought, wow, this is the thing I've been searching for.
Greenstone was able to analyze data that included roughly 40,000 people living in urban areas within a five-degree latitude range north and south of the river. The first outcome he looked at was life expectancy.
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