At the end of 2009 efforts to negotiate a global climate treaty crashed and burned in Copenhagen. At the time, the head of one charity described the city as “a climate crime scene” with “the guilty men and women fleeing to the airport”.

Six years later governments will revisit the scene of the crime—metaphorically at least—when they gather in Paris to have another go at negotiating a climate treaty. This time they will bicker and squabble their way to a deal. Whether it will do much to rein in the growth of carbon emissions or satisfy any of the other hopes that were raised and dashed at Copenhagen is doubtful.

Much has changed since 2009. Most of it makes a deal somewhat more likely. A new generation of leaders has come to power. Indeed, only Barack Obama of the United States and Germany’s Angela Merkel remain as heads of the largest polluters.

The new generation leads a world in which greenhouse-gas emissions have risen remorselessly since 2009. In 2015 annual average concentrations of carbon dioxide in the atmosphere will rise above 400 parts per million for the first time in over a million years. And even though global surface temperatures have not risen much for a decade, the risks of severe and irreversible damage from rising greenhouse-gas emissions are, according to most climate scientists, growing. In most countries (though not in America) climate change is seen as a significant threat.

Outdoor air pollution has become the largest source of premature death in the world. Politicians are also coming under increasing pressure from business, finance and markets. Two big reports published in 2014 (one from an international group of ex-presidents, heads of international financial institutions and economists; the other from American chief executives and former treasury secretaries) demonstrated a substantial change of mind among decision-makers that climate change needs to be tackled.

Some markets reflect these concerns. The corporate green-bond market, for example, which raises money from capital markets for companies to make environmentally friendly investments, is likely to hit $100 billion in 2015; in 2009 it barely existed. As a result, the politics of a climate treaty have changed. In 2009, none of the three biggest national polluters—the United States, China and India—was ready for such a step. Now, they may be.

America’s Senate will not ratify a treaty—these days, it never does—but executive actions by the Obama administration (such as limiting emissions from power stations) have ensured that the United States could abide by the terms of any likely climate treaty, rather as it conforms to the UN Law of the Sea, which it has not ratified.

In China the president, Xi Jinping, has given fighting pollution a higher profile. He has done so for domestic reasons, but may be prepared to approve a treaty based on steps he was planning anyway. India has long been cautious on global climate matters and is likely to remain so. The main reason for thinking it too might move is that its prime minister, Narendra Modi, was something of a green pioneer when chief minister of Gujarat.

It is true that some things have not changed. The Copenhagen talks foundered mainly on disagreements between rich and poor countries. The poor argued that the rich caused more of the carbon accumulation in the first place, and should do more to reduce it by paying poor countries extra to cut back on greenhouse gases. Their demands will grow. The rich replied that they were doing a lot but that developing countries, as the sources of most new emissions, needed to do more themselves. There is little sign that this disagreement has narrowed. Moreover, the European Union, which likes to see itself as a leader of climate talks, has been backing away from some of its recent green ambitions.

Better than nothing

A new climate treaty will reflect such difficulties. Instead of looking like a traditional treaty, in which countries sign up to common obligations and promise to meet common targets, the new deal will allow countries to set their own goals, agreeing merely to revisit them regularly (which would help to give global investors confidence that the market for green goods will expand) and perhaps to promise to make goals more, rather than less, stringent in future.

Such a deal would be extremely modest. In practice it might merely codify what America, China and a few others were doing anyway. It would not be able to push countries into promising anything they do not want to do. But at least it would be something, which is more than Copenhagen managed.

John Parker: environment editor, The Economist