Tuesday, July 21, 2009

Solar Irradiance and Climate Change

The New York Times has an article on the dearth of sun spots this year which also mentions the improbability of their relationship to the cool summer we're having:
The idea that solar cycles are related to climate is hard to fit with the actual change in energy output from the sun. From solar maximum to solar minimum, the Sun's energy output drops a minuscule 0.1 percent.
Most people reading this probably haven't had college and graduate level thermodynamics or heat transfer. Allow me to explain the fundamentals. You do not do heat transfer or thermo in Fahrenheit or Celsius. You perform the calculations in Rankine or Kelvin respectively. These are just the former scales adjusted to zero at absolute zero. With convection and conduction, you can cheat because the temperature terms are linear and so the conversion cancels itself out. With radiative heating you can't take that shortcut because radiation is proportional to the temperature difference to the fourth power.

Why does this matter? It matters because room temperature on earth is around 300 K or 530 R. A 0.1% change in irradiance would produce a temperature shift of ~0.3 C or ~0.5 F. Global warming is credited with temperature shifts anywhere from there up to about a degree Celsius. While small, a simple back of the envelope calculation should show that that change in irradiance is nowhere near negligible in relation to the phenomenon being studied.

Update: Fixed the formatting left over from mailing it in. Did it on the new toy. Liking it so far, especially now that I have Firefox installed.

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