Economists On Climate Change: Do We care?

On the costs of policies, the concern is of over-optimistic assumptions about the update of new clean energy technologies, with recent oil price hikes, for example, spurring less adoption impact than some had expected.

The annual costs of tackling climate change escalate rapidly the tougher the action.

Reilly estimates the cost of staying within a 3 degrees temperature rise at 2 percent of global GDP in 2100, but at some 8 to 10 percent of GDP to stay under 2 degrees - or some $25 trillion in 2100 money - seen as a danger threshold.

Mendelsohn estimated that the top end of possible temperature rises, nearly 6 degrees, would cost up to 2 percent of GDP in 2100.

Britain's Stern will present his findings to ministers in Mexico next week, a month before countries start talks - expected to last years - on a successor to take the Kyoto protocol beyond 2012.