Barack Obama may be forced to delay signing up to a new international agreement on climate change in Copenhagen at the end of the year.

Al Gore, the former US vice-president, delivers an upbeat assessment of the global response to climate change today, saying he believes a "political tipping point" has been reached which will enable leaders to avert environmental catastrophe.

CLIMATE EXPERTS have urged scientists and engineers to find radical answers to global warning, suggesting they might even explore a way of refreezing the North and South Poles.

More bad news on climate change is expected as more than 2,000 climate scientists gather in Copenhagen. They will be trying to pull together the latest research on global warming ahead of political negotiations later in the year.

More carbon dioxide needs to be absorbed than emitted by 2050 in order to prevent catastrophic climate change.