The stars have certainly been aligned in favour of clean-energy stocks early this year, as growing acceptance of the need to reduce greenhouse-gas emissions has bolstered the value of companies with interests in non-fossil-fuel sources of energy.

For 18 months, Nature has been tracking the value of a group of US-based energy companies. But this week we shift attention to an international selection of companies, which reflects the market for clean energy outside the United States. The WilderHill New Energy Global Innovation Index — NEX on the American Stock Exchange — tracks the weighted values of about 60 of these companies around the world.

At least until global markets dipped last week, the NEX index had been moving strongly upwards. The release of the fourth report from the Intergovernmental Panel on Climate Change on 2 February lent further impetus to a corporate trend in favour of clean energy, says Rob Wilder, founder of WilderShares, the California company that co-compiles the index with London-based New Energy Finance. “Even conservative people have been pushing their reservations aside and getting on board,” he says. “They are saying: 'we don't love Al Gore, but there's money to be made'.”

And Wilder notes that quiet and determined corporate moves into the sector — such as a low-key 8 January announcement by US food giant Cargill that it is creating a subsidiary to build ethanol-processing plants — hint at good long-term prospects.

Even the global stock market correction on 27 February, which saw the Dow Jones fall by more than 400 points, confirmed the ebullience of the sector, says Michael Liebreich, head of New Energy Finance. “It was obviously hit by the correction,” he says, “but less so than some main market indices.”