[MUSIC]
One of the simplest positive feedbacks in the climate system is called the ice
albedo feedback.
Albedo is a word that, it means
the fraction of light that gets reflected back out to space.
So when visible light comes in and gets reflected back to space,
it doesn't deposit it's energy as heat to the planet.
We saw the albedo, in the layer model, so the higher the albedo of the planet,
the colder the planet is, because it doesn't use that light
to fuel its own thermal energy, it just loses it off the top.
So, the feedback with ice is that, ice and snow are very reflective.
So if you have a layer of snow over ground,
it will cause the visible light to be reflected back out to space,
it'll have a high albedo.
And then, you make it warmer, and the light then will hit the darker ground and
be absorbed, so this will have a lower albedo.
So if you absorb that light now, it makes the earth warmer.
So going from a cold state to a warm state tends to be
amplified by the melting of the ice.
And so, in this sort of a feedback diagram,
the state variable is the temperature, which gets fed back to.
So a perdibation to the temperature, that makes it a little bit warmer,
causes ice to melt, which makes it warm up even more.
So this is an amplifier.