Carbon dioxide does influence the Earth’s climate, but it is just one variable among a great many, and its impact is small. Scientists agree that if you double the CO2 in the atmosphere, it will cause an increase in the Earth’s temperature of around one degree Celsius. Nearly all scientists also agree that an increase of that magnitude would be good, not bad, for humans.

The minor role played by CO2 is documented in this graph, which I posted here. Over the course of the Earth’s history, the amount of CO2 in the atmosphere has fluctuated widely, but these fluctuations have no apparent relationship to the Earth’s temperature, as best it can be reconstructed.

So where does global warming alarmism come from? The alarmists concede that a doubling of CO2, by itself, would do no harm. But they say that increasing CO2 in the atmosphere triggers positive feedbacks that enhance the otherwise-minimal effect of CO2 on temperature. Even though the feedback effects of CO2 are hotly debated, the alarmists program them into their computer models. This is how they generate scary scenarios where the Earth’s temperature rises far more than could be caused by CO2 itself. This also explains why the models have no predictive value, which is a polite way of saying they are wrong. Because the alarmists just make up a lot of positive feedback effects, and ignore the negative feedback effects, their models reflect fantasy, not reality.

A negative feedback is one which will tend to moderate the impact of the event or phenomenon that gave rise to it. Negative feedbacks are critically important in maintaining various natural balances. There is good reason to believe that negative feedbacks operate with respect to CO2, and that negative feedbacks, in fact, are more substantial than the positive feedbacks on which the alarmists predicate their now-discredited models.

Watts Up With That reports on another in a long series of negative feedbacks that has been documented and quantified: “more CO2 = more plants = more aerosols = cooling.”

As temperatures warm, plants release gases that help form clouds and cool the atmosphere, according to research from IIASA and the University of Helsinki. The new study, published in Nature Geoscience, identified a negative feedback loop in which higher temperatures lead to an increase in concentrations of natural aerosols that have a cooling effect on the atmosphere. “Plants, by reacting to changes in temperature, also moderate these changes,” says IIASA and University of Helsinki researcher Pauli Paasonen, who led the study. … While previous research had predicted the feedback effect, until now nobody had been able to prove its existence except for case studies limited to single sites and short time periods. The new study showed that the effect occurs over the long-term in continental size scales.

The researchers say the effect is relatively small on a global scale, negating around 1% of theoretical global warming. (I can’t tell whether this is 1% of the 1 degree of global warming, or of the higher number that assumes numerous positive, but not negative feedbacks.) However, this now-quantified effect is very significant regionally, negating, all by itself, 30% of theoretically-postulated warming in forested regions. And this negative feedback, of course, is only one of many. The most important feedbacks have to do with the formation of water vapor and clouds. The point here is that until all of the significant feedback effects have been identified and quantified, negative as well as positive, all estimates of the effect of increasing CO2 in the atmosphere are simply bogus. The fact that the alarmists’ models utterly fail to predict actual temperatures proves that they do not adequately take a great many feedback effects into account.

STEVE adds: There’s one seemingly small detail in this story that is likely to be missed by the mainstream media, etc: the role of IIASA in this study. IIASA is no fringe research group that can be marginalized by Al Gore; to the contrary, it has been at the center of much of the “consensus” climate science world. Among other things, IIASA produces the emissions forecasts used by the UN’s IPCC and most of the climate modelers. The fact that IIASA has joined this “skeptic” finding is yet another sign that the whole climate horror show is falling apart. (I’ll add that I’ve always found IIASA’s emissions work to be quite serious and rigorous, even if they, like everyone else, have gotten things badly wrong even over just a ten-year time time horizon. Who could have foreseen shale gas in a computer model?)