3.

IPCC 'measures' uncertainties in terms of level of agreement and consensus and the amount of evidence (theory, observation, models). Uncertainties ask for scenarios. Modern scenario building, French-style, start from combinations of intrinsic uncertainties and it emphasizes the use of scenarios: whatever the scenario may be, one should concentrate on controllability or maitrise, searching for levers of strategic intervention. Scenarios describing worlds concerned about the environment should be decomposed in terms of levers of strategic intervention, say, clean energy, preservation of rain forests and maritime ecosystems, environment-saving conversion of agriculture and exploitation of natural resources.

One must also accept that wen cannot predict. Probable, extrapolated futures of 2100 are rather meaningless because of forecast degradation. Moreover, negative but also positive surprises may occur (even innovations born from serendipity). Or social innovations for that matter, for example, new ways of managing the commons of the earth (read Elinor Ostrom, the other Nobel Prize winner). (Commons are closer to cities and regions, bringing long-term issues closer to home. By the way, the Max-Planck Institute takes commons seriously: a project group is currently studying the Recht der Gemeinschaftsgueter). It is true that non-linear models have greater degrees of freedom than linear ones. The work of IPCC and similar examples of global reasoning tend to play down technological (leave alone social) innovations such as the rise of sustainable energies for fear of sounding less alarmist about the future. But is installing fear is the right strategy? Although the profession of appealing to fear may be the oldest profession in the world.

Summarizing: the present evaluation of 'Climate Change 2007' appears to be of limited usefulness. Minor inaccuracies may be detected. What is really urgently needed, however, is a broader, critical assessment of the work of IPCC and its organization. Pessimists, of course, will be tempted to quote Dorothy Parker: 'Old dogma does not learn new tricks'. One can only hope that critics are not automatically classified as deniers, supporters of the anti-global warming lobby or worse.

[The present comment is based on Drewe, P., Fallacies of global reasoning - more inconvenient truths: ]