A HUNDRED years from now, looking back, the only question that will appear important about the historical moment in which we now live is the question of whether or not we did anything to arrest climate change. Everything else—the financial crisis, the life or death of the euro, authoritarianism or democracy in China and Russia, the Great Stagnation or the innovation renaissance, democratisation and/or political Islam in the Arab world, Newt or Mitt or another four years of Barack—all this will fade into insignificance beside the question of whether we managed to do anything about human industrial civilisation changing the climate of Planet Earth. It's extremely hard to focus on this, because environmentalism goes in and out of political fashion depending on the economy, war, and so forth. But from the perspective of our great-grandchildren, the only thing that's going to seem important is whether we burned all the fossil fuel on the planet and sent global temperatures up by at least 4 degrees Celsius in the next century, or whether we took collective action, shifted our energy sources, and held the global temperature rise to 2 degrees or less.

Actually, I take that back: there are two possibilities. The first is that global warming will seem to have been the overwhelmingly important question, a hundred years on. The other possibility is more depressing, but I'll get to that later.

So, the global climate change conference in Durban surprised most everyone and managed to pull out a deal at the last minute. I found this surprising because unlike other organised bodies that tend to swirl around in terrifyingly chaotic bickering before pulling out a deal at the last second, such as the United States Congress or the European Union, the global climate change conference doesn't have anything immediately at stake for any of the participants. No governments would have fallen if the negotiators in Durban had failed to reach an agreement (more's the pity). And yet they reached one. This seems to indicate that something in the politics of climate change may have shifted a bit.

How good is it? Pilita Clark and Andrew England at the Financial Times have the consensus optimistic take: a European Union team "prodded the conference to achieve what more than a decade of climate negotiations had never done before. Finally the world agreed that every country, no matter how rich or poor, would cut its greenhouse gas emissions under a global pact with 'legal force'". Michael Levi at the Council on Foreign Relations has the pessimistic take: the actual phrase, "a process to develop a protocol, another legal instrument or an outcome with legal force under the Convention applicable to all Parties", was the result of a hard-fought battle by India to block any tight promise of a binding treaty, and "an outcome with legal force" might refer to almost anything with even a little bit of legal force.

Dave Roberts is somewhere in between. As with every bit of climate-change progress, he says, the verdict is: "compared to what's needed, a failure; compared to what's possible, decent." His five takeaways are mostly negative: the world is still on track for more than 4 degrees in temperature hikes even if every country implements every carbon-emissions reduction it's planned; the promise to develop an agreement by 2015 which will become "an outcome with legal force" by 2020 will be just a scrap of paper for a President Romney. But on the bright side, he says, the reason an agreement was reached at all, and the reason it covers the rising economies of India and China, is that the politics of climate change in the developing world have changed. The island states and the Least Developed Countries (LDCs) squared off against India and forced the agreement: they face all the catastrophic results of climate change (desertification, submersion) with no promise of fossil-fuel-driven development. He cites Karl Hood of Grenada: "While they develop, we die; and why should we accept this?" As the impact of climate change hits home at the level of national politics, the issue may finally acquire a desperate, critical constituency. That's the missing ingredient.

I haven't been to Grenada. When I think about the places where climate change hits hardest, the image that comes to mind is the long drive from Mali back through Burkina Faso to Togo, across the barely cultivable brown land of the sahel. These are countries where large portions of the population are still subsistence farmers, where simple habitability is already on a knife's edge, even at incomes and levels of water use a tiny fraction of those in developed countries, and where populations are growing at 2.5% a year or more. If the rest of Mali is buried by the Sahara, where do those millions of people go?

Possibly, that threat will be enough to focus these countries' political interests on climate change as the critical issue of our time, and possibly, that will help lead to a global agreement with teeth by 2020. But there's another possibility, the one I alluded to at the top. Maybe a hundred years down the line, nobody will look back at climate change as the most important issue of the early 21st century, because the damage will have been done, and the idea that it might have been prevented will seem absurd. Maybe the idea that Mali and Burkina Faso were once inhabited countries rather than empty deserts will seem queer, and the immiseration of huge numbers of stateless refugees thronging against the borders of the rich northern countries will be taken for granted. The absence of the polar ice cap and the submersion of Venice will have been normalised; nobody will think of these as live issues, no one will spend their time reproaching their forefathers, there'll be no moral dimension at all. We will have wrecked the planet, but our great-grandchildren won't care much, because they'll have been born into a planet already wrecked.