The Prime Minister has today declared that global warming is the most serious environmental problem. Last month, the government's Chief Scientific Adviser said that it "is the most severe problem we are facing today, more serious even than the threat of terrorism". That seems a little implausible.

All spending involves trade-offs. If as a society we spend more money on reducing carbon emissions, it means we have less money to spend on other things, like ridding the world of unsafe drinking water, or eliminating malaria from Africa. The Prime Minister gets this. But his prioritization is puzzling. If Kyoto were adopted and followed by everyone - even including the USA and Russia - global warming would be delayed by only six years this century. In other words, despite the cost, Kyoto does not solve the problem.

It is also likely that in the future, scientific advances will enable us to reduce man-made emissions without, or with little, impact on our wellbeing. As the price of clean energy drops, and as we develop the likes of hydrogen cars, carbon emissions will reduce. We will be richer and have better technology, and be able to deal with climate change more effectively.