US President George W. Bush said he was prepared to be "constructive" in discussions on climate change yesterday, although he insisted that any agreement depended on the participation of China and India.

Group of Eight leaders, who today begin a three-day summit in Toyako, northern Japan, are seeking to advance from last year's commitment at Heiligendamm when they pledged to "consider seriously" halving greenhouse gas emissions by 2050. Some G8 leaders would like the statement upgraded to "agree to halve emissions", though the US has been reluctant to commit.