is sitting on top of Greenland and Antarctica,

and each year, a little more of it melts into the ocean.

Normally, it would take hundreds to thousands of years

for it all to melt away.

But what if something happened

that caused a massive global melt overnight?

As we slept, sea levels would rise

by a whopping 66 meters.

Coastal cities like New York, Shanghai, and London

would drown in the apocalyptic mass flood,

forcing up to 40% of the world's population

out of their homes.

While all this chaos ensues aboveground,

something equally sinister is happening below.

All that rising salt water will infiltrate

groundwater reserves farther inland,

forcing its way into nearby freshwater aquifers.

You know, the ones that supply our drinking water,

irrigation systems, and power-plant cooling systems?

All those aquifers would be destroyed.

Not good.

On top of that, the ice on Greenland and Antarctica

is made of fresh water, so when it melts,

that's about 69% of the world's freshwater supply

that's going straight into the oceans.

This will wreak havoc on our

ocean currents and weather patterns.

Take the Gulf Stream, for example.

It's a strong ocean current

that brings warm air to northern Europe

and relies on dense, salty water from the Arctic

in order to function.

But a flood of fresh water would dilute the current

and could weaken or even stop it altogether.

Without that warm air,

temperatures in northern Europe would plummet,

and that could spawn a mini ice age,

according to some experts.

That's not even the worst of it.

Take a look at what will happen

when that last 1% of freshwater ice

that's not part of Greenland or Antarctica thaws.

Some of that 1% is sitting in glaciers farther inland.

The Himalayan glaciers specifically

pose one of the largest threats

because of what's trapped inside:

toxic chemicals like dichlorodiphenyltrichloroethane,

or DDT.

Scientists discovered that glaciers like this

can store these chemicals for decades.

But as they thaw, those glaciers release the chemicals

into rivers, lakes, and groundwater reserves,

poisoning each one as they go.

The rest of that 1% is hanging out underground,

mostly in the Arctic tundra,

as something called permafrost.

Permafrost is organic matter that's been

frozen in the ground for two-plus years.

Now, one of the most immediate problems

with thawing permafrost would be mercury poisoning.

That's right: There are an estimated 15 million gallons

of mercury stored up in the Arctic permafrost.

That's almost equal to the amount of mercury

everywhere else on Earth.

On top of that, the organic matter in permafrost

is a tasty meal for microorganisms.

After they digest it all, they fart out

two of the most potent greenhouse gases out there,

carbon dioxide and methane.

Scientists estimate this could double

the current levels of greenhouse gases in the atmosphere,

and potentially cause global temperatures to rise

by 3.5 degrees Celsius compared to today.

That might not sound like much,

but say goodbye to that mini European ice age,

and even rivers and lakes around the world.

They'd evaporate from the higher temperatures

and cause mass droughts and desert-like climates.

And all that extra water vapor in the atmosphere

would fuel more frequent and stronger

storms, floods, and hurricanes.

So all of that newly established coastline on the eastern US

would be one of the last places you'd want to live.

Instead, there would be mass migrations to Canada, Alaska,

the Arctic, and even what's left of the Antarctic.

And you're right, this is probably never going to happen.

After all, there's enough ice right now

to cover the entire continent of North America

in a sheet a mile thick.

So the next time you hear about record-breaking heat

or ultra-powerful hurricanes,

at least you know that it could be worse.

But scientists estimate that if we don't take action

and global temperatures increase by just 1 degree Celsius,

the effects of climate change we already see today

will be irreversible.

So yes, it could be worse,

and it will be if we're not careful.