In a memorable scene in Al Gore's film on global warming, An Inconvenient Truth, the former US vice-president lampoons a cartoon of a pair of scales that weighs the Earth against a stack of gold bars. Gore's point is that any attempt to compare the merits of the two is ludicrous given their relative importance in the grand scheme of things. It would be easy to satirize reports that the organizers of next year's Rio+20 Earth Summit in Brazil are considering a two-week postponement to avoid a clash with celebrations for the Diamond Jubilee of Queen Elizabeth II in the United Kingdom, which they fear will hold more appeal for politicians, particularly those from Commonwealth countries. Easy — but not necessarily wrong. If the world is to address the myriad environmental problems that scientists have identified, then at some point it will have to give them the attention and the priority they deserve. (And that comes from a journal with its headquarters just a few miles from Buckingham Palace — sorry, Ma'am.)

Dogmatic adherence to the protocol is now a political liability.

A good place to start would be the international negotiations on global warming that reopen in Durban, South Africa, later this month. If optimists were right to herald the tentative steps made last year in Mexico as a new dawn following the chaos of the 2009 Copenhagen meeting, then the Durban negotiations must now make a break from the past. Already, familiar battle lines have been drawn, and flags flown on stand-offs such as the future of the Kyoto Protocol, the global agreement that sets targets for emissions reductions. For years, environmental campaigners at the United Nations climate summits would stalk the corridors and the press room and rapidly correct anyone who claimed that the Kyoto Protocol expired in 2012. It was only the first phase of the agreement that would end, they insisted, finding hope in the implicit promise that other phases would follow. No longer — one of the hottest debates at Durban will probably boil down to whether the protocol will continue in its present form at all.

In a Comment on page 291, Elliot Diringer of the Center for Climate and Energy Solutions in Arlington, Virginia (formerly the Pew Center on Global Climate Change) makes the case that it should not. His argument — that the protocol has become an obstacle to international progress and should be consigned to history — will be popular along the interstate in Washington DC.

It is certainly pragmatic: the odds of China and the United States taking on binding emissions targets, for now, he says, are “nil”, which will keep away Japan, Canada and Russia, and so fatally punch a hole below the waterline in the common-but-differentiated approach taken under Kyoto. “A binding-or-nothing mentality,” has underpinned the climate talks for too long, Diringer says. “And the result often has been nothing.”

Advocates of the multibillion-dollar carbon market established across Europe as a direct result of the Kyoto agreement would no doubt disagree with that assessment — as would the US airlines fighting tooth and nail to avoid being dragged into the emissions-trading scheme from next year. Many developing countries, too, would defend Kyoto, if only because it has made no serious demands of them and they enjoy seeing their wealthier rivals squirm.

But the world has changed since the formative years of the Kyoto Protocol in the 1990s, when it neatly allocated its countries into two camps — rich and poor — divided by a common purpose.

As Diringer points out, some 58% of global emissions now come from developing countries, and although a handful of rich nations still bear a heavy historical burden for global warming, it is unrealistic to expect today's politicians, who can barely look forward more than the next four or five years, to look back two centuries into the past.

One of the goals of Kyoto was to make a relatively small dent in emissions, with the prospect of significantly bigger dents to come. Without the world's two largest polluters — the United States and China — on board that now seems impossible. Another goal was to establish and test an international architecture for reducing greenhouse-gas emissions and eventually scale it up. Without the world's two largest polluters, that now seems pointless.

To ditch the agreement — the only global regulation on greenhouse gases — may seem a dramatic move, and in a way it is, particularly for those who have long believed in it. But the implications need not be severe. Europe can, and should, maintain its carbon market and its commitments, just as the offset mechanism developed under the protocol can continue. The real benefits of Kyoto — practical experience and institutional structures — can endure without it.

Like it or not, a dogmatic adherence to the protocol is now a political liability that threatens cooperative action (however limited) over climate change — such as deals to secure finance for the most affected countries to help them with strategies for adaptation. There is no need to kill it. The treaty is already weakened and will prove hard to revive. The Durban meeting should be where the Kyoto Protocol, as we know it, goes to die.