In my previous post I mentioned that the methane concentration in the atmosphere has declined. The current level is about 5 parts per billion, down from 20 ppb about 25 years ago. (On a unit basis, methane is about 20 times as effective as carbon dioxide as a greenhouse gas.) Changes in the way rice is grown in China is probably the cause. for the reduction in methane concentration in the atmosphere. I wonder if the GCM's the IPCC uses to predict future temperature reflect the decline in atmospheric methane concentration.

It is well known that the IPCC still uses the Mann hockey-stick curve for the temperature history of Earth even though it has been discredited. Now there are claims that the IPCC's record of carbon dioxide level in the atmosphere is incorrect. The record is based on ice core samples for the period prior to 1957. It turns out that there were direct measurements made as far back as the mid-ninteenth century. (That is not a surprise, and I always assumed that these were the basis for the carbon dioxide concentration record.) However, those records show much higher atmospheric carbon dioxide concentrations than the ice sore samples, but were ignored by the IPCC. Here is a paper on past carbon dioxide atmospheric concentration.

http://www.wlym.com/~montreal/en/GoreCO2.html

I don't have an opinion on this yet. But, if it is correct, then Al Gore's global warming hysteria is really a fraud.