The developed countries are not going to allow anything like that sharp a distinction this time. In a speech given just before the draft text was released, John Kerry, America’s secretary of state, put particular stress on the “common” in “common but differentiated responsibilities”.

There are various duties—such as an obligation to help pay for action, and a requirement to report on the effectiveness of national actions—that the developed nations want extended to other big emitters with similar “capabilities”. The large developing countries at whom this is aimed have strongly defended a more old-school treatment of differentiation; India is particularly adamant. Many smaller developing countries, though, are open to the attractions of an agreement which expects more from China than Chad. They would not be averse to some of the $100 billion of climate finance a year the agreement speaks of making available by 2020 coming from developing economies that emit a lot of greenhouse gases.

Who needs to do what is one thorny issue; what they should be trying to achieve is another. Since Copenhagen, negotiations have focused on preventing global warming of more than 2°C compared with the pre-industrial era. Paris has seen a striking push, co-ordinated by the developing countries in the “Climate Vulnerable Forum”, for a more ambitious 1.5°C limit. For many countries, most notably those that consist of small islands, it is a way of instilling urgency into the talks. The European Union has voiced some support for this move; Todd Stern, America’s lead negotiator, says a “recognition” of the tougher target should be included in a deal, too.

On the other side, oil-rich countries such as Venezuela and Saudi Arabia oppose any change from 2°C. Language about how such an aim might be achieved is also contentious. Reference to the world’s “decarbonisation” unsurprisingly upsets Saudi Arabia—a switch to “climate neutrality” may become a bargaining chip. However things are worded, it remains the case that the actions that countries have said they will undertake in pre-Paris pledges come nowhere close to ensuring that warming will remain below 2°C, let alone 1.5°C. The timing of any process by which countries might review and revamp those offers, not to mention procedures by which they can show that they are living up to them, is a blizzard of brackets. This is another area where the dreaded “differentiation” looms large.