Ali: The planet is drying at an unprecedented pace, presenting a critical threat to humanity.

That's according to a new study publish understand in the journal "Science advances."

Researchers found that continental drying is having profound global impact that threaten water availability across the globe.

For part of our tipping point coverage, I spoke recently with a climate investigations editor at pro publica, and began by asking him why so much of the Earth is drying out.

>> It's a mixture of climate change and massive overuse of water resources by people that appears to be drying out a continent, according to a new study out of Arizona state university.

And it basically found that rising temperatures are leading to less precipitation in certain places and faster evaporation from both the soil and rivers and surface waters.

At the same time that overpumping of ground water aquifers is quickly depleting resources held in those underground reservoirs.

Ali: Who's driving this problem?

>> It's difficult to parse out the difference between climate change as an effect and the human overpumping of ground water, but those are the two factors.

Of course, it's the I missions from the burning of fossil fuels that is driving the rising temperatures on the planet, and so that is really contributing to a water loss or a water reportioning across the globe.

And the ground water pumping is driven by individual use, by farmers, by corporations, by cities around the world.

It is becoming the fallback kind of bank account, if you will, of water resources that people in groups are turning to as their surface waters are diminished or as droughts deplete the waters for a shorter period of time.

People are looking to those underground reservoirs and pumping more, pumping faster, exploring deeper.

Ali: And the study uses nasa satellite images over the course of 20 years to track the evolution of land that's drying out.

Can you walk us through mechanically how that works, how the satellite images were able to capture this change?

>> It essentially measures changing mass in the spinning Earth, changes in the Earth's rotational orbit.

So it can measure how much volume is in the poles and how much water is underground, and changes in that mass.

And over the last 20 years, it's allowed researchers to be able to tell the difference between one type of changing mass and another.

So now really for the first time these researchers are using that gray satellite data to get a sense of the Earth's total water supply and then to distinguish between how much of the loss of that water supply is for melting glaciers from climate change, for example, and how much is from something like ground water depletion.

Ali: What are we talking about here in terms of total water loss, and also, how has this accelerated over the past 20 years?

>> Researchers caution they don't know where the bottom is, so to speak.

So we don't have a measure of how much fresh water there is to work with.

What we do know is that the accounts that we're working with are quickly being withdrawn.

So we can see the rate of drying that they measured has quickly accelerated, just over the last 10 years or so, since 2014.

They've been measuring for 23 years.

They've seen that rapid depletion from the very beginning.

But it has intensified and accelerated just in the last 10 or 12 years.

So that's particularly alarming.

It's something that led them to write in the paper that this issue is a critical and emerging threat to humanity.

Ali: What do we know about where this is effecting the globe?

Is it happening more in certain parts of the globe, or is it pretty evenly distributed?

>> The study found that drying places are getting dryer faster than wedding places are getting wetter, and it found those drying regions are much, much larger than the places that are getting increasingly welt.

And those drying regions are spread across every continent.

There's substantial drying regions, which researchers now describe as mega regions that constitute much of the southern United States and into Mexico and Central America.

There's a mega drying region that they identified that covered pretty much the whole of Europe and into the Middle East and includes parts of north Africa and again a large swat of south Asia is also part of these mega drying regions.

And what those mega regions constitute is the merging of places that already were known to be losing water or suffering from drought, but they used to be finite or distinct places.

We used to think, for example, of the southwestern united States as being particularly dry, which it is, and suffering from climate change, which it is.

But until recently, we didn't understand that that drying region was spreading across the whole southern part of the country and is extending down into Mexico and into central America, and that it's becoming one large drought plagued or drying out region.

Ali: How much are we able to connect this phenomenon we're seeing around the world with the impact on the inhabitants who live in these parts of the world?

Are we seeing this play out in real-world implications right now?

>> Yeah, absolutely.

The water loss that this research identified is mainly occurring in mid latitude regions, which is where most of the population of the planet resides, and the researchers identified water net loss in 101 countries, and those 101 countries happen to be home to about 75% of the planet's population.

So about six billion people live in the regions that are on balance losing access to fresh water.

Ali: The thank you so much.

>> Thank you.