- #71
mheslep
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Do you have source for that 12%? I read numbers as low as 2% (Lindzen IIRC).WeatherRusty said:...Atmospheric CO2 has increased due to human activities. Not much question about that.
Atmospheric CO2 is without a doubt a significant absorber of infrared radiation contributing approximately 12% to the global greenhouse effect.
Careful. As stated this implies that is all directly from CO2. The ~4W/m^2 figure is for CO2 and ALL other sources combined, including feedbacks. Radiative forcing directly from increased retention of longwave radiation due to CO2 alone is much less:A doubling of the stuff will impose an additional positive radiative forcing of 3.7W/m^ within the troposphere.
http://www.ipcc.ch/graphics/graphics/syr/fig2-3.jpg
Huh? 1266 W/m^2 space, nearly 1000 W/m^2 insolation received at the surface, low latitudes. Where is there room for 'twice' more radiation from the atmosphere?...The Earth's surface receives nearly twice the warming radiation from it's own atmosphere than it does directly from the Sun.
I've always wondered over what part of the EM spectrum solar radiation is measured.Direct insolation has not increased over the past 50 years, the very period of greatest warming.
I don't believe you can isolate the two (internal/external) in a useful way. PDO, AMO, etc can temporarily change factors (i.e. ice and surface albedo) that increase or reduce the heat radiated away from the planet, i.e., which also makes them 'external' forcings (as you use the term), and its not clear to me that the peaks and troughs of the oscillations always 'cancel' each other out rather than having some net radiative effect over time, in particular when they operate over different average temperatures.Coupled atmosphere/ocean phenomena such as the PDO, ENSO and AMO etc. are examples of internal climate variability rather than external forcings and cancel out over their positive and negative phases.
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