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What is the greenhouse effect?

If you believe in Anthropogenic Global Warming (AGW), to what extent is your belief informed by the theory of the greenhouse effect, and to what extent is it informed by the historical temperature record?

  • Due to length limitations, the main question is a bit simplistically framed. But what I'm really asking for is the relative importance of theoretical mechanisms and direct empirical evidence. Theoretical mechanisms are of course also empirically validated, but the empirical validation could occur in different settings. For instance, the greenhouse effect is a mechanism, and one may get estimates of the strength of the greenhouse effect based on an understanding of the underlying physics or by doing laboratory experiments or simulations. Direct empirical evidence is evidence that is as close to the situation we are trying to predict as possible. In this case, it would involve looking at the historical records of temperature and carbon dioxide concentrations, and perhaps some other confounding variables whose role needs to be controlled for (such as solar activity). Saying that your belief is largely grounded in direct empirical evidence is basically saying that just looking at the time series of temperature, carbon dioxide concentrations and the other variables can allow one to say with fairly high confidence (starting from very weak priors) that increased carbon dioxide concentrations, due to human activity, are responsible for temperature increases. In other words, if you ran a regression and tried to do the usual tricks to infer causality, carbon dioxide would come out as the culprit. Saying that your belief is largely grounded in theory is basically saying that the science of the greenhouse effect is sufficiently convincing that the historical temperature and weather record isn't an important factor in influencing your belief: if it had come out differently, you'd probably just have thought the data was noisy or wrong and wouldn't update away from believing in the AGW thesis.

  • Answer:

    The historical temperature record is evidence of a warming trend. AGW is an explanation of how it came about. It is not an "either or" type of question

Peter Flom at Quora Visit the source

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I have experience dealing with large data sets, so am comfortable gleaning meaning out of noisy data.  I always thought there was a lot of scatter in the historical temperature record, but you can see the trend through the noise.  I would give it a B for compelling. I initially gave the greenhouse effect a B for compelling, since the concentration of CO2 is not really that high.  That was until I was asked to help evaluate a new Fourier Transform Infrared (FTIR) scanner at work.  Apparently, the CO2 in 1 inch of normal air is enough to absorb the IR reflection from the sample.  If that's the case, how much can a 60 mile thick atmosphere absorb?!  That kicked it up to A for compelling. What caught my interest early on were glacier pictures: https://www.google.com/search?q=glacier+photos+before+and+after&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ei=DP-pU_ntOs-gogS6hYD4BQ&ved=0CBwQsAQ&biw=1550&bih=944  Took my breath away.  James Balog later made a much more compelling TEDtalk: http://www.ted.com/talks/james_balog_time_lapse_proof_of_extreme_ice_loss#t-18794 So my evaluation of the data that I have seen points to AGW.

John Kes

Between those two, probably theory somewhat more. But mostly the opinions of experts, who I believe know much more about it than me, and are probably motivated to be honest. Or more precisely, the opinions of apparently trustworthy people (and media outlets) who I interact with more directly, who claim there is basically expert agreement on the question.

Katja Grace

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