the Air Vent

Because the world needs another opinion

Archive for January, 2011

Light Scattering by the Earth’s Atmosphere, Aerosols, and Clouds, Part One – Basic Concepts

Posted by Jeff Id on January 2, 2011

Guest post by Steve Fitzpatrick:

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Aerosols are the 800 pound gorilla of global warming.  Aerosols are claimed by many climate scientists to largely ‘off-set’ radiative forcing by GHG’s in Earth’s atmosphere, and to have greatly reduced the rate of global warming1.  The magnitude of the current aerosol effect is very poorly defined, and even the IPCC says that the credible range is from quite low (~0.4 watt/M^2) to very high (~2.4 watts/M^2).  For comparison, the current best estimate of total GHG forcing (all gases, not just CO2) is ~3 watts/M^2.  If aerosol effects are in fact small (for example, near 0.4 watt/M^2), climate sensitivity is almost certainly quite low, and future GHG driven warming will be modest. If aerosol effects are large (near 2.4 watts/M^2) then climate sensitivity is likely much higher, and future GHG driven warming could be substantial.

Uncertainly in aerosols allow a huge amount of ‘wiggle room’ to climate models (and climate modelers!).  Since almost any assumed historical aerosol profile is acceptable, assumed aerosols can be (and in fact have been) ‘tuned’ to have each model’s hind-cast reasonably match the known temperature record since the late 1800’s.

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Greenhouse Thought Experiment – Id’s Answer

Posted by Jeff Id on January 2, 2011

I waited until my answer was posted in the WUWT thread.  I have replicated it here as well.

Ok, so the point of this thought experiment was to engage the public in a consideration of the differences between the greenhouse effect and an actual greenhouse.  Most here already know that the name itself is a misnomer, but by considering the physics of what is going on we can better understand the argument and better present our opinions on the subject.  The majority of the answer below was emailed to Anthony yesterday before he ran the post at WUWT with the note- just to make sure I can’t back out!  I wrote the reply in terms of energy Joules, it would be more accurate to say power Joules/Sec or Watts but since the system is stabilized the answer works  fine.

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Greenhouse Thought Experiment

Posted by Jeff Id on January 1, 2011

This post is now replicated at the center of the internet.

Derek has been in a war with ScienceofDoom over the what appears to be Planck radiation.  I’m actually not sure of his position because it doesn’t make sense yet to me but he left a thought experiment on the thread which could make for some interesting discussion.  Some will find it pretty easy, while I bet others will get all tied in knots over it.  As a suggestion, taking a thought experiment to an extreme is often a good way to identify a preferred design path or to understand differences in similar situations.  I will give the answers in the coming days, they are already written so I can’t back out but as you consider them I’ll warn that this post is not about the subtleties but rather about the bulk differences.

I’m going to paraphrase Derek’s experiment below and then add another of my own.  If it’s not the exact same as his it doesn’t matter the idea is still interesting.

For our experiment assume we have a bolometric camera for measuring emitted thermal radiation as an image.  IOW a cool toy which in this case happens to detect all EM wavelengths with perfect sensitivity.  To be clear, the camera integrates to measure the radiative emission temperature of the object.

We have two plants, one is contained in a transparent box (greenhouse) the other in open air, both thermally stable (temperature isn’t changing).  We take an image of the two plants in the early afternoon on our fancy camera, what do you find in the image?

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