Leading article: A small, green step for the good of everybody

THIS WEEK the environment ministers' caravan moved on from Rio, via New York and Kyoto, to Buenos Aires. The great Save the World from Global Warming tour has been to more summits than Chris Bonington. Progress is slow, but that is the way of diplomacy and this is a problem that can be tackled only by concerted action by all countries.

People will not use less energy if they are simply asked politely to do so. Behaviour will change if the price of energy changes. That requires international agreement to impose higher taxes on fossil fuels. The crucial breakthrough was at Kyoto, when the US agreed to legally binding targets. Green purists have attacked the idea that the US should be allowed to buy the right to emit carbon dioxide from Russia, but this establishes a vital second principle: that saving the environment should be accompanied by transfers from rich to poor nations.

All power to John Prescott's elbow as he tries to put these principles into practice in Argentina. Yesterday's announcement that the US would sign the Kyoto agreement was largely symbolic as it has yet to get through the gas-guzzling Senate. But it was another small step along the mountain range of green summits.