There has been an enormous shift in opinion in recent years about climate change. Scientists and political leaders are now united over the threat and the need for action. But there is a danger of a chasm on the size and speed of the cuts to greenhouse gas emissions we require.

Scientists say cuts of between 25 per cent and 40 per cent in industrialised countries by 2020 are essential to hold temperature rises down and lessen the risk of catastrophic, irreversible climate change.

But with global carbon emissions growing at over 1 per cent a year, political leaders question how they can deliver such drastic reductions without damaging prosperity.

Nicholas Stern, the author of the 2006 review on the economics of climate change, may have demonstrated that the cost of delay in tackling climate change would be many times higher than taking action now. But politicians who think only of the long term and ignore immediate public concerns may find themselves in office only for the short term, replaced by those without their vision.

So the challenge is to agree on national and international action to deliver low-carbon economies, but in a way that allows people - including those in the poorer parts of the world - to enjoy the material and social benefits of growth and consumption. This needs a framework sufficiently radical about where we have to go but realistic about where we are now and the speed of travel.

It's a task, given the complexity of the issues involved, more difficult than any the international community has faced during the past 50 years. But it is vital, given the potential price of failure, that agreement is reached at the UN conference in Copenhagen next year.