Let’s be as generous as we can. The IPCC say feedbacks amplify CO2′s warming by a factor of about three.
So being nice people, let’s assume it’s warmed since 1979 and assume that it was all due to CO2. If so, that means feedbacks are …. zero. There goes that prediction of 3.3ºC.
Feedbacks are the name of the game. If carbon dioxide doesn’t trigger off powerful positive feedbacks, there was and is no crisis. Even James Hansen would agree — inasmuch as he himself said that CO2 would directly cause about 1.2ºC of warming if it doubled, without any feedbacks (Hansen 1984).
Consider the warming from1979 to 2007, when we measured temperatures using satellites and not corrupted and adjusted land thermometers. Douglass and Christy (2008) point out that, given how much CO2 levels increased in that time, the warming only amounts to what the IPCC scientists predict we should get from CO2 alone, from the direct effect of CO2, and not from the effect of CO2 plus positive feedbacks.
The warming trend expected from CO2 without any feedbacks at all is 0.07 ºC/decade. The trends from the UAH satellites are 0.06±0.01ºC/decade. Since the two figures are almost the same, no one needs a super-computer to tell them that this implies that the sum of all feedbacks (and the sum of all fears) is zip, nada, nothing.
Furthermore, this study likely overestimates the effect of CO2. There is clearly a 60 year cycle of warming and cooling due to the Pacific Decadal Oscillation, and the 28 year study period was the steepest part of that 60 year cycle. Hence, trends over longer periods are likely to be smaller, which implies that feedbacks are negative.
Thus the upper bound on climate sensitivity (the temperature rise when CO2 doubles) from the last three decades of warming is about 1°C, and that’s assuming all the warming is due to CO2 increases and not due to other factors like solar magnetic effects, cosmic radiation, ocean current oscillations, or geomagnetic forces. Which is much less than the IPCC median estimate of 3.3°C.