AMNA NAWAZ: Right now, India is one of the hottest places on the planet, and much of this past month has been brutal.

But South Asia is hardly the only place suffering extreme heat.

It's still May, and temperatures are already abnormally high in some parts of the U.S., Mexico, and elsewhere.

William Brangham has the latest.

WILLIAM BRANGHAM: Amna, temperatures in India's capital, New Delhi, where 35 million people live, reached 122 degrees Fahrenheit this week.

It's driving reports of heat-related deaths and illnesses across the country.

At night, the temperatures are still well over 90 degrees.

At the same time, New Delhi is also dealing with a critical water shortage.

Residents are struggling day to day.

SATISH KUMAR, Driver (through translator): I keep myself hydrated.

I drink water, lemon water, and protect my head with a piece of cloth.

I sit in the shade and drink buttermilk to benefit.

Otherwise, it is too hot out here.

Because of heat, our conditions have gone from bad to worse.

There's no relief, even from shade sometimes.

I have to drink five, six liters of water every day in the afternoon.

WILLIAM BRANGHAM: Across the world in Mexico, where there's a drought as well, howler monkeys have been dying off in 100-degrees-plus heat.

Here in the U.S., Miami just recorded its hottest May on record, with temperatures in the 90s and a heat index approaching 110.

They're expecting triple digits in Phoenix this weekend.

To help us understand more about what's driving this, we are joined by Andrew Pershing.

He is the director of climate science at Climate Central.

Andrew, thank you so much for being here.

First off, what is driving this?

Is this as simple as global climate change, that, as we continue to warm the planet and the atmosphere, that we see more of these extreme events?

ANDREW PERSHING, Climate Central: Yes, to a first approximation, that's exactly right.

We are on a warming planet because we have too much carbon dioxide in the atmosphere.

One of the most obvious signs of that is that we see these extreme events popping up all over the world.

And I think, especially as you look at the number and the fact that they're occurring simultaneously in so many places, that's a really clear signal that we live on a planet that has a climate that is -- has been altered by people.

WILLIAM BRANGHAM: What do you say to the devil's advocate who says, look, it's almost the cusp of summer, it's naturally warm in the summer, warmer in the summer, and, of course, we're going to see some spikes in temperatures, that that -- that this is not that unusual?

ANDREW PERSHING: I would say this is actually quite unusual, right?

That's what the data and the science suggest.

Absolutely, we can talk about any one of these places and it will have hot weather and it will have had hot weather in the past.

But the conditions you're seeing in India, these could not occur without climate change.

Many of the -- the pervasive heat that we -- that you talked about in Mexico, that almost certainly could not exist without climate change.

It's not just -- it's also the severity, but it's in some ways when it occurs, right?

Early season heat, that is a sign of climate change.

And it's the duration, right, how persistent the heat is in many places around the world.

WILLIAM BRANGHAM: Are there other factors beyond climate change that could be driving this in different locations?

ANDREW PERSHING: Weather happens, right?

You have natural weather variability in terms of where a heat wave sets up.

Things like El Nino are going to drive the patterns, like the blobs of heat and how they move around the planet.

But the fact that we're seeing so many of these events taking place all over the world at the same time, that's a very strong indication that climate change is behind much of the pattern that we're seeing.

WILLIAM BRANGHAM: Your organization, Climate Central, just put out this study looking at the increase in extreme heat events globally.

Can you tell us a little bit about what that study found?

ANDREW PERSHING: Sure.

We focused on days that anybody at that location would find hot for that location, right?

So, it's going to be a hotter temperature in Phoenix than it is in Boston.

But we looked around the world, and what we found was that climate change added, for the average person planet Earth, 26 extra days of extreme heat.

It's really an incredible burden that we're putting on people around the planet.

And it's even higher if you move into places like Central America, Northern Africa, and places in Southeast Asia.

WILLIAM BRANGHAM: As you're indicating and as your report touches on, extreme heat doesn't fall proportionately on all members of society.

Can you talk a little bit about the people who suffer the most when the temperature goes way up?

ANDREW PERSHING: Sure.

So, when the temperature goes way up, the people who suffer the most are the people who are already vulnerable for one reason or another.

So it could be because they're very old or very young or have some sort of underlying health condition.

And that underlying health condition could be pregnancy.

People who are pregnant are highly vulnerable to heat.

But then you add in these kind of social vulnerabilities.

If you are homeless and living on the street, you're going to be very highly vulnerable.

That's what -- that's what folks see in Phoenix during their extreme heat events.

I believe it was like 80 percent of the deaths came from their unhoused population.

People who are who are abusing drugs are going to be more susceptible.

So any of these kind of social vulnerabilities are going to magnify the potential that -- for a bad outcome.

WILLIAM BRANGHAM: Are there things that -- I mean, we know that cutting the emissions of greenhouse gases is the number one way we can tackle climate change globally.

But, on a local level, are there things that people can do, that governments can do to protect those most vulnerable people when the temperature soars?

ANDREW PERSHING: Absolutely.

And that's, I think, one of the really unique things about heat relative to other kind of major climate-driven weather events, like major hurricanes or things like that, is that there's a lot that we can do individually and as communities to keep people safe in the heat, right?

Individually, you can take care of yourself, drink water, like, understand where your options are to stay cool and keep an eye on your friends and neighbors, and then, for things like cities, systems that help keep -- get the more - - most vulnerable into cooling centers.

Things that you can do around, planting trees or lightening the surface of a city to reflect some of that radiation back into space, those can help keep the environment cool.

WILLIAM BRANGHAM: All right, Andrew Pershing of Climate Central, thank you so much for being here.

ANDREW PERSHING: Well, thanks for having me.