The reason for slightly cooler mid-century temps is natural variability and some contribution of sulfur aerosol blocking. The climate response in increasing atmospheric greenhouse gases is not expected to be linear; given that virtually everyone, skeptic or non-, will state that climate is a complex system, I fail to understand why there's an expectation of a simple correlation between increasing atmospheric CO2 and higher temperatures!
I concur, and that is the point I'm trying to make. The GW crowd has consistently harped on CO2 as the leading greenhouse gas and blah, blah, blah. According to Dr. Baliunas, There are 11 key gasses that comprise our atmosphere and climatologists understand how fewer than half of them affect overall temperature.