THE Intergovernmental Panel on Climate Change (IPCC), set up
under the auspices of the United Nations to establish a
consensus on global warming and what to do about it, has now
completed its fourth assessment report. The first two parts,
published earlier this year, about the science and the impacts
of climate change, were designed to spread gloom. Change was
happening, they said; it was mankind's fault; and it was going
to be damaging. The third part, released on Friday May 4th in
Bangkok, is about mitigating climate change, and is designed to
spread hope. Just as mankind caused the problem, it says, so
mankind can stop it—and at a reasonable cost.  In some areas of
economic activity, emissions could be cut with no cost to
consumers or taxpayers. The heating and lighting systems of many
buildings, for instance, are startlingly inefficient. Improving
this would cut both emissions and bills. Economists are troubled
by this, for it implies that people and businesses are not
maximising their economic self-inter