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[♩INTRO]
In July 1983, a weather station in Antarctica recorded the lowest air temperature
ever measured on Earth.
It was about -89 degrees Celsius…
which is colder than the average temperature on Mars.
But 25 years later, scientists analyzing satellite data found small pockets
high up on the East Antarctic Plateau where temperatures routinely drop
about five degrees lower, making them the coldest spots we know of on Earth.
But these pockets aren’t just for record books:
They’re also helping us understand how cold it’s possible to get
on the surface of our planet—and what conditions it takes to get that cold.
These record-breaking temperatures happen during long polar nights
within little hollows in the ice sheet,
more than three-and-a-half kilometers above sea level.
On still nights when the sky is clear, the air near the surface of the snow cools
down as heat radiates into space,
and it becomes denser than the slightly warmer air surrounding it.
As a result, it starts sliding downhill along the ice sheet
and sinks into these hollows.
If the wind is light enough, the super-cold air gets trapped down there,
and it acts like a kind of ice pack,
which brings down the temperature of the surface even more.
When that happens, the air temperature drops down to those record low
until weather stirs things up again.
But the lack of wind isn’t the only thing you need to get those temperatures.
It also has to be extremely dry,
because water vapor can keep heat from escaping.
See, heat might feel like this abstract thing,
but it’s just waves of infrared radiation.
So when heat escapes our planet,
infrared waves are radiating from the ground and into space.
When temperatures drop, there’s less heat coming from the surface,
so the waves carrying that heat away lose energy and stretch out.
And those longer waves are more easily absorbed by water vapor in the air.
So if there’s any moisture in the air,
a lot of that radiation won’t escape into space;
it will be absorbed by the water and sent back to the ground to warm things up.
In fact, to get below about -90 degrees, you need less than a millimeter’s worth
of water in the entire atmosphere stretching from the ground all the way into space.
In other words, if you wrung out all the water from that air,
it wouldn’t even reach the one-millimeter line on a rain gauge.
Those are some strict requirements.
But for the researchers studying this, the really surprising thing wasn’t just that
the temperature got so low in these pockets:
It was that, over time, it dropped to nearly the same low temperature
over and over again.
Like, across 14 years and hundreds of kilometers of the Plateau,
the lows at the coldest sites hovered right around -94 degrees,
just above the all-time low of -98.
So scientists wondered if the temperature was hitting some kind of threshold
if it was reaching the coldest temperature possible on the surface of our planet.
And that seems to be what’s happening!
See, even on still, dry nights, the heat doesn’t radiate away forever.
Instead, a lot of that infrared radiation gets trapped by carbon dioxide
because while CO2 always absorbs some heat,
it’s especially good at absorbing these longer wavelengths.
So at that point, the air itself is trapping heat
and sending it back toward the surface.
The atmosphere essentially acts like a blanket,
and heat can only escape from the surface really slowly.
Eventually, around -98 degrees Celsius, the temperature is dropping
less than half a degree a day
too slowly to really change before the weather shifts and winds stir things up.
In theory, if air could sit still for days or weeks on end,
the temperature could drop lower, but on a planet with so much weather,
-98 degrees is essentially as cold as it gets.
Which, hey, is fine by me.
It takes some creative thinking to find and demystify something
like the coldest place on Earth.
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[♩OUTRO]