Under its provisions, nations have made voluntary pledges to begin reducing their carbon emissions. These are modest - the United States, for instance, plans to cut carbon dioxide emissions by 2025 by 12 per cent to 19 per cent from their levels in 1990. As the scrupulous scorekeepers at Climate Action Tracker, a non-governmental organisation, put it, that's a "medium" goal "at the least ambitious end of what would be a fair contribution".

And that's about par for the course here. Other countries, like petrol station owners on opposite corners looking at each other's prices, have calibrated their targets about the same: enough to keep both environmentalists and the fossil fuel industry from complaining too much. They have managed to provide enough financing to keep poor countries from walking out of the talks, but not enough to really push the renewables revolution into high gear. Secretary of State John Kerry, in a fine speech, doubled the US contribution to US$800 million (S$1.1 billion), which is more than Congress is likely to appropriate, but risible compared to the need.

So the world emerges, finally, with something like a climate accord, albeit unenforceable. If all parties kept their promises, the planet would warm by an estimated 3.5 deg C, above pre-industrial levels. And that is way, way too much. We are set to pass the 1 deg C mark this year, and that's already enough to melt ice caps and push the sea level threateningly higher.

The irony is that an agreement like this adopted at the first climate conference in 1995 might have worked. Even then it would not have completely stopped global warming, but it would have given us a chance of meeting the 1.5 deg C target that the world notionally agreed on.

Instead, as we now know from recent revelations about Exxon Mobil, those were exactly the years the fossil fuel industry set to work to make sure doubt replaced resolve. Its delaying tactics were cruelly effective. To meet that 1.5 deg C target now would require breakneck action of a kind that most nations are not really contemplating.

At this point we would need to leave almost all remaining coal and much of the oil and gas in the ground and put the world's industries to work on an emergency basis building solar panels and windmills.

That we have any agreement at all, of course, is testament to the mighty movement that activists around the world have built over the last five years. At Copenhagen, world leaders could go home with nothing and pay no price.

That's no longer true.

But what this means is that we need to build the movement even bigger in the coming years, so that the Paris agreement turns into a floor and not a ceiling for action.

We will be blocking pipelines, fighting new coal mines, urging divestment from fossil fuels - trying, in short, to keep weakening the mighty industry that still stands in the way of real progress. With every major world leader now on the record saying they at least theoretically support bold action to make the transition to renewable energy, we have a new tool to work with.

And we will try to keep hoping that it adds up fast enough to matter. That's a little hard, as the hottest year ever measured draws to a close. One doesn't want to rain on the Paris parade - but that's what seems to be happening somewhere every day now.

Like Washington state, where high temperatures and heavy rainfalls led the governor to declare a state of emergency late last week, as landslides closed highways. Or Portland, Oregon, which had the rainiest December day in its recorded history. Or Norway, which had the worst flooding in more than a century of record keeping. Or…

NEW YORK TIMES

• The writer is the founder of 350.org, a global grassroots climate campaign. He teaches environmental studies at Middlebury College, a liberal arts college in Vermont, the United States.