Today brings the beginning of the most important international gathering since the second world war. Recent progress now means that if we are wise and collaborate at the 15th session of the conference of the parties to the United Nations framework convention on climate change, an effective and equitable agreement is within reach. But there is also a danger of division, deadlock and failure.

In Copenhagen over the next two weeks, governments will attempt to hammer out an organisational framework, backed by political commitments, to limit the risks from unchecked emissions of greenhouse gases. That can provide the basis for a strong treaty next year to succeed the Kyoto protocol.

Carrying on as we have been risks a rise in global average temperature of 5?C or above to levels our planet has not seen for more than 30m years. Humans, who have been here for only 200,000 years, have never experienced global average temperatures on this scale. It would be likely to lead to the movement of hundreds of millions of people and extended, severe conflict.