Feedback governing climate change
A very interesting and well-written article on one aspect of our climate -- feedback.
The Anthropogenic Global Warming folks consider that there is positive feedback. The Earth warms, more water vapor comes into the atmosphere trapping more infrared radiation causing the Earth to warm even more.
This idea has their panties in a bunch and is the cause for the hoopla and sub-prime science.
Today, at Watts Up With That,
Anthony has a guest post from professor Richard Lindzen, PhD (Alfred P. Sloan Professor of Meteorology, Department of Earth, Atmospheric and Planetary Science, MIT) with observational data that implies the positive feedback model is a false one and that there is a very large and very observable negative feedback driving our climate:
Lindzen on negative climate feedback
Simplified Greenhouse Theory
The wavelength of visible light corresponds to the temperature of the sun�s surface (ca 6000oK). The wavelength of the heat radiation corresponds to the temperature of the earth�s atmosphere at the level from which the radiation is emitted (ca 255oK). When the earth is in equilibrium with the sun, the absorbed visible light is balanced by the emitted heat radiation.
The basic idea is that the atmosphere is roughly transparent to visible light, but, due to the presence of greenhouse substances like water vapor, clouds, and (to a much lesser extent) CO2 (which all absorb heat radiation, and hence inhibit the cooling emission), the earth is warmer than it would be in the absence of such gases.
The Perturbed Greenhouse
If one adds greenhouse gases to the atmosphere, one is adding to the �blanket� that is inhibiting the emission of heat radiation (also commonly referred to as infrared radiation or long wave radiation). This causes the temperature of the earth to increase until equilibrium with the sun is reestablished.
For example, if one simply doubles the amount of CO2 in the atmosphere, the temperature increase is about 1�C.
If, however, water vapor and clouds respond to the increase in temperature in such a manner as to further enhance the �blanketing,� then we have what is called a positive feedback, and the temperature needed to reestablish equilibrium will be increased. In the climate GCMs (General Circulation Models) referred to by the IPCC (the UN�s Intergovernmental Panel on Climate Change), this new temperature ranges from roughly 1.5�C to 5�C.
The equilibrium response to a doubling of CO2 (including the effects of feedbacks) is commonly referred to as the climate sensitivity.
Dr. Lindzen delivers the money quote:
From 1985 until 1989 the models and observations are more or less the same � they have, in fact, been tuned to be so. However, with the warming after 1989, the observations characteristically exceed 7 times the model values. Recall that if the observations were only 2-3 times what the models produce, it would correspond to no feedback. What we see is much more than this � implying strong negative feedback. Note that the ups and downs of both the observations and the model (forced by observed sea surface temperature) follow the ups and downs of temperature (not shown).
The 200+ comments are well worth reading as well...
Posted by DaveH at March 31, 2009 5:05 PM