A spring gale is lashing orthodox climate policy. This week, an article was published in Nature that should shake the certainty of anyone who assumes that the Kyoto protocol approach is the sensible way to go, and that signing the accord is a responsible step for the United States to take. Three climate experts offer some inconvenient truths. Roger Pielke, Tom Wigley and Christopher Green are far from being climate change sceptics, but they are vigorous heretics about some of the orthodoxy of the debate. They show it is even more urgent than we thought to abandon the failed Kyoto strategy and move quickly to policies which might actually reduce carbon emissions. Any workable strategy has to include India and China: Kyoto did not. As they rapidly industrialise and reduce poverty, their CO2 emissions will rise steeply - by as much as 13% a year for the period from 2000 to 2010, in the case of China. The Nature piece is titled "Dangerous assumptions". The most dangerous assumption is how all the scenarios that the UN Intergovernmental Panel on Climate Change (IPCC) has published have a built-in assumption that misleads us about the magnitude of the emissions challenge. It shows that the technological challenge is at least twice as big as people believe. So this is where the rubber hits the road. The IPCC has assumed that about three-quarters of the emissions reduction required to stabilise CO2 will occur "spontaneously". It would arrive as a free rider on the back of the well-documented trend which indicates that, after an initial upswing, the energy intensity of industrial societies has a record of impressive and continuous decline. What does that mean? Energy intensity is an elegant and potent function which shows the relationship, over time, between a standardised unit of production - say