There is much for the world to be pessimistic about these days. The double crises of the Ebola outbreak in West Africa and Islamic extremism in the Middle East, for example, pose real dangers. So it says much for the one-day United Nations summit on climate change, held in New York City last week, that not only did it receive widespread media coverage, but also the enduring message sent by the meeting was one of optimism.

There have been enough ‘turning points’ in the politics of the effort to curb global warming to send anyone dizzy. That is the narrative the story demands: incremental progress is boring; grand gestures are preferred. Every meeting and announcement is the most important, at least since the previous one.

The politics and the science of climate change have long since parted company. The science demands political action to aggressively curb greenhouse-gas emissions. The politics, as the saying goes, is a bit more complicated than that. But it is politics, not science, that offers the opportunity for intervention. (The science, of course, can help to guide policy, as is explained in a Comment on page 30 on the absurdity of the 2 °C target for global temperature rise.)

If last week’s meeting marked a political turning point (and these things are best judged from a distance), then it came with the first signs that the world’s largest economies (and worst polluters) are at long last forging an alliance. Even so, the message that seeped from many speeches and presentations was sobering: the combustion of fossil fuels that powers mobility and production in the globalized economy and that keeps our homes warm will probably lead to greater climate change than civilization can easily handle. There is no easy way out of that situation. But although time is running out, the world is not yet doomed.

One lesson, at least, does seem to have been learnt. The top-down approach to emissions reductions — binding caps and legally mandated targets for cuts — is a logical response to the climate problem, but an unworkable one. Global warming is a real and omni­present risk, but it proceeds slowly and is essentially un­observable to the general public. Unlike escalating epidemics or savage acts of terrorism, a shifting climate has not forced societies and policy-makers to make it a priority. Despite headlines about extreme weather, that is unlikely to change.

The ultimate goal of closing the door on the fossil-fuel age seems far off.

Given this political reality, if a new global agreement to tackle climate change is to be agreed by the end of next year — as the UN schedule dictates — then it cannot follow the top-down model of the Kyoto Protocol. But the legal architecture and modes of operation of a contrasting ‘bottom-up’ agreement remain to be defined. Parties to the United Nations Framework Convention on Climate Change must yet resolve such thorny issues as compliance, verification of reported emissions, and rules of emissions trading. Such technicalities, which often prove to be pitfalls, do matter. But if China, the United States and the European Union — the world’s largest emitters — pull together as they have promised, then a meaningful international climate agreement is well within reach.

Will such an agreement limit warming to 2 °C? Almost certainly not. Will it respond appropriately to the scientific evidence of the scale of the likely threat? Definitely not. Is it the best the world can do? Probably.

Regardless of its specifics and legal force, however, a climate agreement will not ‘save the world’, but nor would a failure of the Paris climate summit in December 2015 automatically mean Armageddon.

The binary rhetoric that campaigners tend to apply in environmental matters does not do justice to the complexity of the task at hand. It would be too easy to blame this or that government for not doing enough when man-made climate change is really the result of collective economic activities, past and present, that cannot be broken like a habit. Key to coming to terms with the unprecedented dilemma we face is effective international cooperation across all aspects of economic and social life, with the ultimate goal of closing the door on the fossil-fuel age.

That goal seems far off, given the continued lure of oil and gas and the huge amount of ‘locked-in’ emissions from the army of new coal-powered plants in China and elsewhere. And the world population keeps growing: by mid-century, when global emissions will already need to have declined substantially to avoid excessive warming, billions of ‘consumers’ in Africa and Asia will remain trapped in the fossil-fuel age regardless of the low-carbon technologies that might then be available — unless they are helped out of poverty. Rich countries, meanwhile, must improve their public transport systems, encourage energy-saving construction and invest in grids and energy-storage technology that can accommodate the ebb and flow of electricity from renewable sources. Without these and countless other steps, any climate agreement will ultimately fall short.