Global warming hysteria has been driven largely by the United Nations’ Intergovernmental Panel on Climate Change, which has issued four politically-driven and, in crucial ways, inconsistent reports. The IPCC is now working on report number five, and the current draft has been leaked. It contains a bombshell that may or may not survive in the final product; but in the meantime, the cat is out of the bag.
This is the background: climate alarmism is based in substantial part on the assumption that other causes of global warming can be accounted for, and whatever is left over must be due to human-emitted CO2. This sort of reasoning is rarely valid, but it is particularly inappropriate in a field as little understood as climate. One obvious reason why the Earth has gotten warmer and colder over the millenia is that the amount of energy put out by the Sun varies. Moreover, over the last few centuries, sunspots–considered to be a good proxy for solar activity–have correlated very closely with Earth temperatures. More sunspots equal higher temperatures.
It shouldn’t be a surprise that variations in the Sun’s output are responsible, at least in part, for variations in Earth’s temperatures. The problem is that if you simply do the math on radiant heat, the known increase in solar activity during the second half of the 20th century accounts for only a small portion of the assumed increase in temperature over that period. So the alarmists have denied that the Sun plays a significant role. More recent work has strongly suggested that solar radiation plays a role above and beyond radiant heat, by influencing cloud cover, which is a key factor in temperature. Given the strong correlation between solar activity and temperature, this work has been persuasive.
So that is the admission that was leaked yesterday. The current draft of the IPCC report says:
Many empirical relationships have been reported between GCR or cosmogenic isotope archives and some aspects of the climate system (e.g., Bond et al., 2001; Dengel et al., 2009; Ram and Stolz, 1999). The forcing from changes in total solar irradiance alone does not seem to account for these observations, implying the existence of an amplifying mechanism such as the hypothesized GCR-cloud link. We focus here on observed relationships between GCR and aerosol and cloud properties.
So the IPCC, at the moment at least, stands ready to admit that the evidence supports a much larger role for solar activity, and a correspondingly much smaller role for CO2. Of course, other sections of the report implicitly contradict this admission. Watts Up With That has all the details on the controversy. I am not sure I agree with those who say this represents the death knell for climate alarmism, but it certainly does illustrate how flimsy the “science” underlying the hysterical position is.
STEVE adds: I may add a separate post of my own about this later, but it is worth pointing out that we reported the backstory to this issue here on Power Line in August of last year.