In light of this illuminating admission, we note that the setting aside of key uncertainties in the climate modeling enterprise could well lead to more extreme possibilities at both ends of the climate prognostication spectrum, such that not only may earth's surface air temperature rise somewhat more than is predicted by the current IPCC consensus, it could equally as easily rise somewhat less than that august group has opined. And for the IPCC's current full range prediction of 21st century warming (1.1-6.4°C), somewhat less warming could well turn out to be indistinguishable from no warming at all.

But how could this possibly be? The answer may well be found in the implementation of another important principle enunciated by Oppenheimer et al., i.e., their contention that the basis for quantitative uncertainty estimates "must be broadened [our italics] to give observational, paleoclimatic, or theoretical evidence of poorly understood phenomena comparable weight [our italics] with evidence from numerical modeling."

As a prime example of important paleoclimatic evidence that has been largely ignored by the IPCC, we cite the stunning results of the many studies we continue to identify and analyze in our Medieval Warm Period Project, where each week we highlight the findings of a different paleoclimatic study that reveals the time domain and various climatic characteristics of this probably warmer-than-present century-scale period of a thousand years ago, when the atmosphere's CO2 concentration was only about 70% of what it is today. A repeat performance of whatever caused that earlier warm period (it was clearly not a spike in the air's CO2 concentration) may well be what brought about the Little Ice Age-to-Current Warm Period transition; and its possible full or partial reversal some time over the next 93 years could well result in the mean global air temperature in AD 2100 being equal to -- or even less than -- today's mean air temperature. Likewise, an example of a poorly understood phenomenon of truly huge climatic significance is the means by which small changes in solar activity are able to bring about significant changes in climate. As Lean (2005) describes it, "a major enigma is that general circulation climate models predict an immutable climate in response to decadal solar variability, whereas surface temperatures, cloud cover, drought, rainfall, tropical cyclones, and forest fires show a definite correlation with solar activity."

In a display of open-mindedness uncharacteristic of most climate alarmists, Oppenheimer et al. go on to suggest that "a special team of authors could be instructed to examine the treatment of unlikely but plausible processes," stating that such analyses might even be conducted by "competing teams of experts." Unfortunately, past findings of the IPCC are already driving massive political and governmental actions throughout the world; and backtracking -- which is what the implementation of Oppenheimer et al.'s suggestions would effectively constitute -- simply cannot be tolerated by those who have invested so much political and economic capital in the reigning climate-change paradigm of CO2-as-global-warming-demon ... unless, of course, people suddenly come to their senses and begin paying attention to all of the pertinent scientific literature, as we attempt to do here at CO2Science.

Sherwood, Keith and Craig Idso

References
Lean, J. 2005. Living with a variable sun. Physics Today 58 (6): 32-38.

Oppenheimer, M., O'Neill, B.C., Webster, M. and Agrawala, S. 2007. The limits of consensus. Science 317: 1505-1506.