- The 2020s may go down in history as the decade of heat waves.

And as we begin to realize just how dangerous heat is, scientists around the globe are racing to find harm reduction solutions.

In the US, a policy that caused nearly a century of problems might actually help shed light on how to cool the hottest neighborhoods.

This goes much deeper than air conditioning because counting on it alone not only warms the climate but also strains vulnerable electrical grids that power it.

In 2021, when the northwest US was hit by its most extreme heat wave on record, Vivek Shandas documented something very unexpected.

- So I looked at my phone, saw 111 degrees, saw 115 degrees, and immediately thought, "A lot of people are gonna die."

- And they did, more than 750 in the US and Canada.

- We saw these large temperature differences across neighborhoods and even individual streets next to each other.

That difference is life and death.

- But that large temperature difference also presents a very clear path forward.

In order to survive coming heat waves, we need to make the hottest neighborhoods more like the coolest ones.

But why does that difference exist?

And how can we change hot neighborhoods to cool them down?

We'll find out and list the top five things that actually cool neighborhoods when it matters most.

(gentle music) As we've shown in a previous episode, cities are warming much faster than the undeveloped areas around them.

They're also growing quickly while the underlying climate is warming.

- We've had a very stable weather system for human habitation for about 10,000 to 11,000 years, and suddenly we're seeing rapid transformation of that climate system, which translates to our daily weather.

You put that together with the fact that we have more people living in cities than ever before in human history, and that's two trains heading right towards each other, and we're trying to figure out, how hard is the collision of those two trains?

- So to help answer this question, Vivek and his team developed mobile thermometers that could be attached to cars or bikes and taken out into the city to collect data and create detailed temperature maps.

- It's a really hot day and what I like to do is come out, get these devices set up.

And so we take this, put it in the backside over here, and then I'm gonna turn this guy around so it collects the air going forward, roll the window up.

It's connected to the satellites overhead, the GPS that's telling us exactly where we are, and we're off and running to collect temperatures for the day.

(mellow music) Six feet above the ground, two meters above the ground, we would think that air has had a good chance to mix and that the hotter air would go towards the colder air, the colder air would go towards the hotter air, and we would get this kind of convective mixing, which is really what kind of stabilizes the temperature.

- [Maiya] But when Vivek drove to different Portland neighborhoods to measure temperatures during the 2021 heat wave, he found something totally different.

- Well, we found a temperature difference of about 25 degrees, which is the largest air temperature difference I had ever recorded in this city.

And as we started going out and systematically collecting data in these different cities, we started seeing very similar patterns.

And so then the question became, what had to happen in these cities decades ago in order for these patterns to emerge?

And one of the most significant things that happened decades ago was a federal policy called redlining.

- In the 1930s, the federal government began a program to prevent large numbers of foreclosures in the wake of the Great Depression.

Banks would create loans guaranteed by the US Government using a series of maps to rank neighborhoods A through D. D neighborhoods were determined to be the highest risk and marked in red.

The primary criteria for risk were race and ethnicity.

Black and Latinx people were considered the riskiest, but in places like Chicago, Italians and Russian Jews were considered almost as risky.

Buying a home in a C or D area was difficult or impossible.

In the 1970s, these maps were publicly released along with notes from the surveyors, and if you have any hope of them not being terribly racist, I'm sorry to do this, but here's Cate Mingoya with a surveyor's note.

- It's from Richmond, Virginia, it's for a neighborhood that was graded C, and it says, "Respectable people but homes are too near the negro area D2."

That means that the very proximity to blackness was enough to steal an opportunity for economic growth and prosperity from an entire neighborhood of people in Richmond, Virginia.

- But what does that have to do with heat today?

- That means that you're kept from the benefits of home ownership, that means that you are not going to be able to maintain your property by doing things like improving drainage and making changes like planting trees.

Additionally, people who were living in redlined neighborhoods, their property values were a lot lower, which meant that the taxes for homes in that area were also a lot lower, so you see things like sewage infrastructure not being updated, parks not being cited there, trees not being planted in the public right of way, so there's a really long process of disenfranchisement.

- And we're still feeling the impacts of that nearly century-old policy.

- It turns out that the color scheme that was set up helped to explain what was happening in terms of difference between one neighborhood and another neighborhood.

We were able to find that, in looking at 108 cities across the country, 95% of them, meaning the vast majority, followed a very similar pattern to where the D hazardous neighborhoods were consistently hotter than their A, best neighborhoods.

(gentle music) - Okay, so what's the difference between these neighborhoods?

This is the intersection that recorded that 124 degree temperature that was the hottest temperature recorded during last year's heat dome.

There aren't a lot of trees here so there's not a lot of shade in this neighborhood, and you got a lot of pavement.

Let's actually compare this neighborhood to the coolest neighborhood.

Here it is, the coolest neighborhood, with an air temperature of 99 degrees.

There's tons of trees in this neighborhood and it's surrounded by forests, so we got a lot of trees, a lot of shade.

25 degrees cooler, though, 25 degrees.

But I'm glad we're here, I'm glad we're seeing this in person 'cause it just gives us a map of what we can do in hotter neighborhoods to make them safer.

- Tree cover and shade saves people's lives.

It's just that simple, whether it's a senior who doesn't have any air conditioning or just as simple as folks that are waiting for the bus right now.

If you see this bus stop, they're lucky because there's a big, ol' tree there, and guess where everybody's sitting?

Up under the tree.

If you look down this way, there are bus stops down here and there are no trees, right?

And there are many, many, many bus stops in the city that have no trees.

Where we are today is Jackson Ward, which is a traditionally African American neighborhood.

It's hot in this part of the city and there are not enough trees.

And with development, trees get taken down and little ones get put up, and so we're constantly in a battle of trying to maintain the tree canopy.

So we've planted a few hundred trees.

We're watering, at this point, 400 trees this season.

- Trees are not the whole solution, but according to everyone we talked to, planting trees, protecting existing, and maintaining your city's trees is the best way to cool urban areas.

Next, decrease impervious surfaces by removing any pavement that can be replaced by something else or something more efficient.

Add shade structures to public places like transit stops.

That could be planting trees or building roofs.

Promote air convection and mixing by encouraging a variety of building heights in all neighborhoods, especially near water, and work with prevailing wind directions to be sure tall buildings aren't blocking airflow from other neighborhoods.

And finally, add surfaces that cool the area, like green roofs, green walls, white roofs, and water features in public spaces.

After helping discover the extreme temperature differences we've been talking about, folks at the Science Museum of Virginia went to work on transforming two acres of pavement on their campus into green space.

- Right now we're standing on top of a brand-new four-story parking deck that consolidated the area that we needed for our parking for our guests, allowing us to do something extremely dramatic to the former surface parking lot that we would use for that same purpose, namely de-paving it and turning it into a civic green space for us, our guests, and all of our neighbors here in Richmond.

What's really special about this, I think, is that it represents, to our knowledge, one of the largest de-paving projects in the city's history.

When we look at the different types of options that we have, unfortunately, parking, green space, housing, and businesses have all been kind of put in opposition to one another, when, actually, responsible land use allows us to take advantage of the very limited space that we do have to maximize the benefit for our neighbors and our visitors here at the science museum, as well as around the city.

So when we think of it, parking, housing, green space, and business development do not need to be in opposition.

In fact, they should be all seamlessly integrated to provide the best opportunity for climate resilience for our neighborhoods that we can provide.

- Friends of Trees has been working on the issue for quite a while, and that shows just how long it'll take to reverse a century of lack of investment.

What is Friends of Trees doing in neighborhoods like this to keep them cooler?

- Our mission is basically to plant trees alongside community members.

In our 33-year history, we've planted over 900,000 trees and native shrubs.

Due to several factors like development and heat waves, we're barely maintaining.

In fact, we're losing canopy in a lot of these East Portland neighborhoods where we need that canopy the most.

What we do try to plant is more drought-resistant trees because as the heat waves are coming, what we're finding is certain trees are struggling to survive.

This is a climate emergency.

We should be planting as many trees as possible to help kind of restore some of the wrongs of the past as a community.