earth sciences and ecology question #3836

Greg Kutz, a 30 year old male from Calgary asks on April 13, 2007,


It truly seems that the world is indeed warming up and I do believe it is being caused by us. However, what is the irrefutable evidence that this warming is anthropogenic in nature (CO2 in particular)? I've been doing some research but can't seem to find the answers I'm looking for. I am a chemist (analytical) so I am familiar with much but not all of the terminology and logic in the field. I'm also aware of how incorrect it is to even challenge the notion. Could you point me in the right direction?

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the answer

Anonymous Canadian government scientist answered on April 17, 2007, A:

[Editor: Due to the political nature of this question, the answerer wished to remain anonymous.]

My personal view is that the climate guys do have their act together on this. The 2007 United Nations Intergorvernmental Panel on Climate Change (IPCC) report says the probability that observed climate trends are man-made is "very likely". The IPCC defines "very likely" as 90-99%. (See "summary for policy makers" on Wikipedia.) The evidence is huge piles of understanding and studies, the vast majority of which indicate the same thing to one degree or another. I don't think they say this is "irrefutable"; IPCC didn't use their "virtually certain" (>99%) category. It is a policy issue to decide at what level of probability one should act.

[Editor: I would add that virtually all the studies cited by the IPCC are climate modeling studies based on mathematical computer models of global climate trends. Evidence is created by running the models with "natural" non-anthropogenic forcing variables only to find the temperature stays more or less constant. They then take the same model and put in anthropogenic forcing factors and they get a big effect in the model's predictions. This is the evidence.]

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