There’s a reason that summers in the city are so hot,
and it’s probably easiest to explain why
with thermal vision.
It shows the heat all around me
and also the coldness of this ice cream cone.
Cities are often hotter than their suburbs
due to a phenomenon known as “the heat island effect.”
All of that asphalt,
concrete,
dark rooftops
and tall buildings—
they absorb and store heat.
And there are a lot of people using a lot of energy—
driving cars, riding subways, running the AC.
All of these materials and activities
either create or retain heat.
And all that stored heat causes steeper nighttime highs …
when people would otherwise have a chance to cool down.
The way all these heat-storing elements are laid out
matters quite a bit.
In cities laid out in grids,
like Phoenix, Chicago, or Washington, D.C.,
the buildings are closer together,
like closely packed coals in a fire, keeping heat in.
More space between buildings
creates more circulation.
Another way to combat this heat island effect
is through green space.
Parks, trees, plants—
they don’t absorb as much heat …
they actually send water back in the atmosphere.
Between all those hot buildings, that cools things off.
Another solution is color.
Light colors reflect sunlight back into the atmosphere
instead of storing it as heat.
It's easiest to see in crosswalks,
and it's true for the color of buildings
and other urban surfaces, too.
And one long-game way to combat the heat island effect
is to avoid using air conditioning when you don’t need it.
AC uses a ton of electricity and creates a feedback loop.
When we get that electricity from coal or natural gas,
that puts more carbon dioxide into the atmosphere …
which warms the planet …
making cities even hotter.
But this isn’t just about comfort.
Today, heat waves kill more people
than any other extreme weather event.
More than tornadoes, hurricanes and even floods.
City populations keep growing,
and those cities are only getting hotter.
This is Let's Talk, NPR's news explainer show.
Make sure to subscribe to our YouTube channel and check out other shows.
I'm Christopher Joyce, and this is NPR.