When the world's most powerful political leaders convene at the G8 summit next week in the German spa town of Heiligendamm, they will bring with them pre-prepared communiqués on most of the topics to be discussed, from the financial risks of globalization to the need for development aid in Africa.

But the eight heads of states will also carry with them responsibility for most of the world's annual greenhouse-gas emissions. Angela Merkel, the German Chancellor, who hosts this G8, wants the leaders at Heiligendamm to agree a concrete plan on how to substantially lighten this load in the next couple of decades.

The Bush administration, however, seems once again to be working to foil any meaningful progress by the G8 on climate issues. Merkel should learn lessons from what happened to UK prime minister Tony Blair when he sought to pursue the same agenda at the G8 at Gleneagles, Scotland, two years ago: by accommodating US resistance and talking compromise, he achieved precisely nothing.

This time, Merkel should hold her ground, refuse to include inadequate climate-change language in the final communiqué and, if necessary, dismiss G8 protocol and break publicly on the issue with Bush and any allies he can muster. She should be encouraged in such a stance by the presence of US House speaker Nancy Pelosi (Democrat, California), who is visiting Europe this week. Pelosi's trip, in effect, aims to remind both Europeans and her supporters at home that the Bush administration no longer speaks for America on the climate-change issue.

The G8 leaders are uniquely placed to confront the issue of global warming.

The G8 leaders are uniquely placed to confront the issue of global warming. Negotiations at the United Nations' upcoming climate summit in Bali will be led by environment ministers, diplomats and subordinate government delegations. They are doomed to failure in the absence of a clear and unambiguous political mandate from above.

The G8 summit can best achieve that by stating unequivocally that the negotiations in Bali must achieve a robust and effective follow-up to the 1997 Kyoto Protocol, which required countries to reduce their greenhouse-gas emissions by an average 5% relative to 1990 levels in the 2008–12 commitment period.

Such a follow-up agreement needs to include the active participation of the United States and timelines for the involvement of India and China. It will probably involve fresh, mandatory caps on emissions and an expanded cap-and-trade scheme modelled on Europe's emerging carbon market, modified to incorporate tax-based incentives to reduce emissions. Kyoto may have been a flawed agreement but there is no going back on the concept of an international treaty, led by the developed countries but involving developing ones too, as a central component of a global strategy to curtail emissions.

Participants in the G8 summits have built these gatherings up, over many years and in the face of considerable public scepticism, as the very pinnacle of global democratic leadership in the developed world. Failure to lead on the climate issue next week can suggest only that the scepticism was justified.