The Earth's climate system is powered by the sun. Our planet intercepts 340 W m-2 of solar radiation averaged over the surface of the globe. About 100 W m-2 is reflected to space, and the remainder-about 240 W m-2-heats the planet. On a global average, the Earth maintains a radiative balance between this solar heating and the cooling from terrestrial infrared radiation that escapes to space. When a particular human activity alters greenhouse gases, particles, or land albedo, such activity results in radiative imbalance. Such an imbalance cannot be maintained for long, and the climate system-primarily the temperature and clouds of the lower atmosphere-adjusts to restore radiative balance. We calculate the global, annual average of radiative imbalance (W m-2) to the atmosphere-land-ocean system caused by anthropogenic perturbations and designate that change radiative forcing.We know quite well what the concentrations of greenhouse gases (not just CO2) were 100 years ago. We even have an idea about 1000 years ago and futher back from ice core studies. So people do compute routinely the radiative forcing and find that it has increased.
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posted by pax digita at 8:04 AM on June 15, 2007 [2 favorites]