Tuesday, December 1, 2009

The Science of Global Warming

It's been a while since I last covered global warming. With the upcoming Copenhagen talks, it is back in the news...

The leading proponents of anthropic global warming (AGW) constantly plead with us to listen to the science. Of course, science is an abstract noun. And abstract nouns hate it when you anthropomorphize them.

And then, they don't even tell us the science. They just tell us to trust them. Like this article from Ars.

So, I have dug into the science for myself. The basics are pretty straightforward, and we can see where the difficulties lie:

It all starts with the Sun.

The Sun is a huge nuclear furnace (operating at almost 16 million degrees K). Inside, hydrogen becomes helium, with small amounts of matter converted to energy. This energy spills out into the outer layers of hydrogen, until it reaches the surface (at a temperature of about 6 thousand degrees).

The Sun can be modeled as a "black body", one which is in equilibrium (emitting as much energy as it receives). This gives us an idea of the sort of light coming from it, and allows us to calculate the energy received by the Earth (intensity of about 1.4 KW/m^2).

Modeling the Earth is much more complicated. If the Earth were a true black body, the surface temperature would be about 278 K (5 C, or 41 F - pretty cold).

Actually, the surface of the Earth can be modeled fairly well as a black body (or actually, gray body with some albedo/reflectiveness).

The trouble comes in that the energy emitted by the surface is not radiated directly into space.

We calculate the wavelength of light emitted based on temperature. For the Sun, with its high temperature, the light is what we call "visible" - short wavelength. The Earth, with its lower temperature, emits infrared light (long wavelength).

The atmosphere passes visible light (low absorption), but absorbs infrared light. This creates the "greenhouse effect". The atmosphere acts like a blanket or insulator, reflecting some of the infrared back to the Earth, before passing any out to space.

Modeling the effects of this blanket is the hard part...

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