Schneider is absolutely right to ask for more realistic probabilities about this range of scenarios; for how can one formulate a rational response to potential climate change (or even decide if a response is needed) if everything from the low-end to the high-end of the predicted warming range is considered equally likely to occur?  Furthermore, if this equal-likelihood probability assessment is even close to correct, one must acknowledge that even more extreme scenarios, at both the high and low ends of the predicted global warming range, are clearly possible; for real-world probability distributions are not square-wave functions that drop precipitously to zero when one exceeds or falls below some magical upper or lower limit.  And acknowledging this fact leads to the realization that a rational extension of the IPCC's predicted global warming range below its stated lower limit of 1.4°C could well come very close to a value of 0°C, indicative of little to no warming at all.

Acknowledging such a state of uncertainty, however, is the same as saying one has not the foggiest notion what the future really holds for earth's climate, which is totally unacceptable to those who use the threat of global warming to advance their dreams of global governance.  Nevertheless, taking this route is the only way they can give their worst-case scenario any credence; and so they take the chance that the public will not recognize the logical ramifications of their position, knowing full well that the media and many well-meaning, as well as many not-so-well-meaning, environmental organizations will be rapidly drawn to the most extreme of their predictions, and that in a grandiose perversion of the precautionary principle they will hype its implications to the highest heavens.

If you doubt our assessment of the situation, we direct your attention to what happened in the wake of the IPCC's release of its most recent climate change report.  The majority of the media, almost to a person, focused on the most extreme value of the IPCC's predicted global warming range (Noyes, 2001).  Did the media do so because this most extreme prediction was the most likely to capture the interest of their patrons?  Probably, for predictions of impending doom generally garner high readership and viewership.  And, as recent history has strikingly verified, this predictable response of the media has indeed had the effect of putting enormous pressure on the government of the United States to take action on a global political agenda that has next to nothing to do with climate change but everything to do with the promotion of a set of revolutionary economic and social policies that are so repugnant and counterproductive they could never be enacted on their own merit.

Fortunately for the entire biosphere, including us, the U.S. government has not seen fit to capitulate to the powerful forces unleashed by these brazen but brilliant tactics, which ride roughshod over logic and data alike; and this bit of respite provides us the time to more thoroughly consider the question of Schneider.  So let's back up a bit and do what the IPCC's generals refused to do, even at the urging of one of their own, and try to associate some probabilities with their predicted range of global warming.

Perhaps the best thing we could do in this regard is regurgitate the results of the study of the seven scientists who produced the 73rd report of the Massachusetts Institute of Technology's Joint Program on the Science and Policy of Global Change (Webster et al., 2001), who recently used quantitative uncertainty techniques to assess the ultimate consequences of "cascading uncertainties in natural and anthropogenic emissions of all climatically important substances, both gases and aerosols, in the critical atmospheric, oceanic and geochemical interactions, and in the carbon-cycle feedbacks from terrestrial ecosystems and the oceans."  Using an integrated earth systems model, the MIT scientists found, first of all, that "there is far less than a 1 in 100 chance of a global mean surface temperature increase by 2100 as large as 5.8°C," which really puts the lie to the IPCC's claim that that degree of warming is equally as likely to occur as any other within the range they specified.  Second, the global change researchers found that the median projected warming from 1990 to 2100 was only 2.5°C, which is significantly less than the 3.6°C median warming predicted by the IPCC; and they determined, last of all, that the lower bound of the 95% confidence interval about their median value was located all the way down at a value of 0.9°C, which is getting pretty close to indicating, as we mentioned earlier, that there could well be little to no CO2-induced warming at all, even as predicted by the models.

Of course, the MIT probability assessments are also far from certain, as are all climate model predictions; for as Schneider has rightly said of this cascade of uncertainties, "uncertainties in emissions scenarios feed into uncertainties in carbon-cycle modeling, which feed into uncertainties in climate modeling, which drive an even larger range of uncertain climate impacts," which makes the whole process incredibly suspect from the very start.

But what is uncertainty when there's a political agenda to be pursued and a world to be conquered, albeit by bureaucratic regulation?  All's fair, it seems, in love and war -- and political climatology!

Schneider, S.H.  2001.  What is "dangerous" climate change?  Nature 411: 17-19.

Webster, M.D., Forest, C.E., Reilly, J.M., Sokolov, A.P., Stone, P.H., Jacoby, H.D. and Prinn, R.G.  2001.  Uncertainty Analysis of Global Climate Change Projections.  Report No. 73. MIT Joint Program on the Science and Policy of Global Change.  Massachusetts Institute of Technology, Cambridge, MA.