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Hillwilliam -> RE: An Attempt to Understand the Science Behind Global Warming (9/28/2013 9:14:09 PM)
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Not quite Ken
We see materials as transparent, translucent, reflective or absorptive.
One thing that a lot of folks have a hard time wrapping their minds around is how something that looks transparent can actually be reflecting or absorbing certain wavelengths.
Radiant energy is just photons. Photons have wavelengths that can be measured in Kilometers (radio) all the way down to the approximate size of an atomic nucleus (gamma).
It's all a form of 'light' but we can only see a tiny portion of it. (Visible Spectrum from Red to violet)
Any substance will have a spectrum denoting what wavelengths it transmits, emits or absorbs. This is how things have color. Transparent substances are transparent to visible light but they DO absorb or reflect other wavelengths we just don't see it.
The sun shines. Some wavelengths are reflected or absorbed by the atmosphere. The really nasty stuff is deflected by the magnetic field.
Most of it is transmitted.
Light hits the earth. Darker areas (land & water) absorb it and grow warmer. Icy areas reflect it back into space and warm up a lot less.
Land is constantly reradiating 'light' back into space in the form of Infra Red photons.
That's right. Visible light was absorbed but a totally different wavelength is emitted.
Ideally, the exact same amount of energy is absorbed and emitted over time. When this happens, the planet stays the same average temp.
Now, let's play with the gas mixture.
Several different gasses including CO2 and Methane transmit the visible light that went down but they reflect the IR that's coming up and trying to escape right back down to the planet. It's not a blanket like you're used to cuddling up with on a cold night as much as it's like a thin foil one way mirror.
More greenhouse gas = more heat reflected back to the ground instead of escaping to space.
The problem is that it doesn't take a lot to upset the balance. The warming won't happen all at once but over decades and centuries.
An analogy would be if you had your exercise and diet exactly homeostatic until your weight never varied and you were a lean, mean athletic machine.
Now, what happens if your activity stays the same but you only eat 10 more calories a day?
You slooowly gain weight and in a few decades you're a fat fucker. (It happens to a lot of us[:(] ) from only 10 more calories a day.
The same thing can happen to a planet.
Lets go back to our model. Remember that ice that was reflecting heat? It's getting less and less now so the land and water can absorb more and heat up faster so that accelerates the process.
In our weight analogy, you see you've gained 15# and get depressed so you eat more accelerating the process.
I hope that helped some folks with the VERY basic scientific principles behind warming. (In practice, it's a fuck of a lot more complex because of differential albedo, ocean currents, etc)
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