The earth and the moon are basically the same distance from the sun, yet temperatures on
the moon average an unlivable -18°C, and even deadlier, they range from -170°C during
lunar night to 100°C at lunar noon, regularly exceeding both the coldest and hottest temperatures
ever recorded on Earth. And while the days and nights on the moon are about 14 times
longer than those on Earth, our planet’s relatively fast rotation isn’t what spares
us from those loony temperatures. What protects us is our atmosphere. By day,
it serves as a shield, blocking out the most harmful and energetic of the sun’s rays
and about one-third of the less-intense visible light. At the same time, it traps the infrared
radiation – aka heat – radiating out from Earth’s sun-warmed surface, keeping us from
freezing solid at night. In order for our atmosphere to absorb any
kind of radiation, it needs to have some electrically charged particles for passing electromagnetic
waves to push around. And most of our atmosphere is made up of gas molecules that don’t have
an electric charge – they all have a balanced number of positive protons and negative electrons.
But some hold most of their negatively-charged electrons closer to one side, lending them
a lopsidedness that can jiggle back and forth to absorb the energy of incoming infrared
rays. For example, water, ozone, and nitrous oxide are all electrically lopsided, so they
all absorb infrared radiation. Then there are gases like carbon dioxide and
methane. On paper, neither molecule looks lopsided, so it doesn’t seem like they should
be able to absorb any radiating heat. But in reality, gas molecules aren't motionless
– they crash into each other billions of times per second, knocking each other in different
directions, and also into different modes of rotation and vibration. And it turns out
that both carbon dioxide and methane spend most of their time “shaking it” in electrically-lopsided
ways, allowing them to absorb infrared rays and help insulate the earth.
Even though many different kinds of molecules can absorb infrared radiation, the vast majority
of our atmosphere can’t, because it’s made of nitrogen and oxygen, which don't get
lopsided even when they are vibrating - they’re too symmetric. Nevertheless, the lopsided
1% are such good infrared absorbers that they manage to intercept about 90% of Earth's outgoing
heat. Each captured ray gets pinged around the atmosphere, and most end up returning
to the surface at least once before escaping to space.
We don’t need to visit the moon during frigid lunar night to know just how important the
game of radiation-pinball is for Earth – ice records from our own coldest climate show
that small, natural variations in atmospheric carbon dioxide produce relatively big changes
in temperature. They also show that, compared to the last 800,000 years, the game today
is much, much harder.
Thanks so much to the great team over at Kurzgesagt for doing the animations in this video, it’s been a lot of fun working with them! And if
you liked what you saw, you can go to the link here or in the video description to check
out their channel, where they cover everything from neutron stars to fracking to the Islamic
State. Thanks again, Kurzgesagt. And thanks as well to everyone who has supported us on
Subbable.com, which has now merged with Patreon.com – you make MinuteEarth possible.