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Recently I watched the 2004 movie The Day After Tomorrow
for the first time,
out of,
a sense of morbid curiosity.
If you've not seen it,
good.
It's a disaster movie about abrupt climate change,
melting of Arctic sea ice destabilizes the thermohaline circulation,
A conveyor belt that transports warm water from the equator to the North Atlantic,
where it warms the land around it before sinking into the deep ocean.
In the movie, this current is turned off, causing an outbreak of extremely cold air
across the northern hemisphere
that creates supercell storms, bringing in a new ice age.
Whilst watching, I made a few notes on the scientific accuracy of the film,
which I wrote on this piece of paper here.
Lots has been said about the scientific inaccuracies of this film.
A new Ice Age wouldn't begin in a matter of days.
The ISS doesn't spin like that.
The movie doesn't know how climate models work.
And how does a single climatologist
afford
You can read stuff about the climatological accuracy of this film elsewhere
Suffice to say, it's incredibly inaccurate.
But there was something in it that was so nonsensical
that it was like watching water flow uphill.
And yet no one is talking about this.
So in this video, I'm going to talk about what that mistake was
and correct it and show you what would actually happen.
Which is still kind of cool
and actually still in keeping with a disaster movie.
The physics breaking problem is in this clip.
“The storm's rotation is pulling
super cooled there all the way down from the upper troposphere.”
“Shouldn't the air warm up before it reaches ground level?”
“It should, but it doesn't.
The air is descending too rapidly.”
“When this storm is over,
we'll be in a new ice age.”
We see this happening later on in the film when the Empire State Building freezes
solid from the top down.
With temperatures as low, we're told in another scene
as -150 freedom units,
or approximately -100 degrees Celsius,
which is cold enough to freeze helicopter fuel.
That's
That's not
That's not how
That's not how physics
That's not how physics works!
Right, Atmospheric physics 101.
Let's say you have a bunch of air at a certain temperature.
How could that temperature change?
Well, you could do two things add heat to the air
or do work on the air.
Both are important here.
The heat one is easier to understand.
You may have learned in school that there are three mechanisms
by which heat can be transferred to an object.
Conduction, convection and radiation.
Conduction is when stuff touches other stuff and makes it warmer.
It's like thermal energy being directly handed from one substance to another.
Convection is when warm stuff moves to colder stuff and mixes with it.
The thermal energy is moved by a carrier.
And radiation is when stuff yeets energy
in the form of electromagnetic radiation to other stuff, which then absorbs it.
The energy moves itself as a photon.
It doesn't need a carrier.
In the atmosphere conduction just isn't a concern.
Air does not conduct heat well.
Convection, however, is what dominates the heat transfer on short timescales.
Warmer air mixing with cooler air while oversimplifying
radiation is what dominates on the longer time scales.
It's what ultimately determines climate.
“Shouldn't the air warm up before it reaches ground level?”
“It should, but it doesn't, the air is descending too rapidly”
If the air were to move extremely rapidly down
through the atmosphere, then as I've already said, conduction isn't a concern.
And radiation acts on longer timescales.
So we could pretty safely ignore that too.
Conceivably, the air could move in such a way that convection wasn't
significant either.
If the descending air mass was particularly fast, and coherent.
So let's say for the sake of argument that there's no heat transfer at all,
no convection takes place,
and the air mass is what we call thermally isolated.
But even if the air in the clip is thermally isolated,
2 problems!
Firstly, the air in the upper troposphere where they say in the film where the air is from,
isn't -100 degrees Celsius,
it's probably more like -70 degrees Celsius at the polar regions.
Above that, the air temperature actually increases without altitude before
gradually falling again in the mesosphere,
I've made a whole video about this.
For air to be cold enough to freeze helicopter fuel,
it would have to come from the top of the mesosphere,
the coldest part of the atmosphere at about 80 kilometers above the surface.
The second problem, however, and this is the water flowing uphill part,
has to do with
As you get higher in the atmosphere, the air pressure decreases.
This is because air pressure is just the weight of air above you and
so the higher up you go, the less weight there is above you and so less pressure.
That means, however, that if a chunk of air were to descend
from the upper atmosphere to the lower atmosphere,
it would be moving from an area of lower pressure to an area of higher pressure.
And as isn't some solid incompressible thing
that means
that the air would be compressed by that additional pressure.
Doing so performs work on the air
and for a system where no heat transfer is taking place,
as we’ve already established, doing work on the system means
the temperature will change, specifically it will increase.
We call this adiabatic heating, and it's actually what largely determines
the temperature profile in the lowest part of the atmosphere
as air rises it cools adiabatically, like this.
Note that the difference between these two curves is almost entirely
just because there's water in the atmosphere,
which kind of makes all the thermodynamics a bit more complicated.
So conversely, if you were to take air from the top of the troposphere
and squidge it down to the surface, it wouldn't be very cold.
In fact, it would be very hot depending on where you are,
between 50 and 100 degrees Celsius.
I can say that with absolute certainty because
"the temperature of a bit of air, if you were to squidge it down to the surface",
is actually a variable that we use quite frequently in atmospheric science.
We call it the potential temperature and it's useful for a variety of calculations.
We construct maps like this where you can see the average potential temperature
with latitude on the horizontal axis and height on the vertical.
Note that towards the middle of the stratosphere.
The potential temperature is about a thousand kelvin or 700 degrees Celsius.
So if you were to somehow drag air down from higher up in the atmosphere
to the Empire State Building, it wouldn't freeze it
because it's not enough to just consider the heat transfer in the atmosphere.
You also have to think about the work done in moving a compressible gas like air
from a low pressure environment to a high pressure environment
near the surface. Air from the upper atmosphere
then would not freeze the Empire State Building.
It would roast it.
And if you took the air from a high enough in the atmosphere
would actually melt it.
In fact, it would not look too dissimilar from a shot in another
far better Roland Emmerich movie.
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Brilliant.
Thank you so much for watching the video.
Thanks also must go to my old professor Myles Allen at Oxford
who introduced me to this scene in the film years ago.
I hadn't seen the movie then, but he introduced me to it and
it stuck in my brain.
I knew I had to make a video about it someday, so thanks, Myles.
Here's some recommended viewing from me next.
If you enjoyed this video, please do pop it like
and let me know in the comments
because I'd love to do more stuff that mixes movies and science.
Kind of my jam.
Anyway, thank you so much for watching.
I hope you enjoyed and I'll see you in the next one.