In 2018, leaders plan to assess their efforts to date and discuss what further action could help lessen the odds of drastic global warming — with the goal of crafting newer, stronger national pledges by 2020. But before they can do any of that, they need to agree to formal ground rules for that exercise. That “rule book” will be a focus at Bonn.

How do countries plan to make progress on climate change?

One widely recognized problem with the current Paris pledges is that they’re fairly vague.

China promised that its emissions would peak around 2030, but the country’s energy data is notoriously murky, so it’s hard to tell how much progress it’s actually making. Similarly, the European Union vowed to cut emissions 40 percent below 1990 levels by 2030, but offered few specifics on how to achieve that goal — making it hard to gauge whether European policymakers could realistically be doing much more.

At Bonn, negotiators will be discussing how to make these pledges more rigorous and transparent, so that countries can more readily be held accountable for their actions. That means tackling questions like: What’s the best way to track nations’ progress, to see if they’re doing what they said they would do? Is there a way to tell if a country’s pledge could be made more ambitious? Which specific policies are working well and which aren’t?

Because the Paris pledges are largely voluntary — world leaders would have never agreed to a deal otherwise — no one can force governments to take additional action. But, the idea goes, if pledges and policies are made more transparent, world leaders will be better able to pressure and help each other to do more.

The final draft of this “rule book” is not due until next year, and it may not actually get finished at Bonn, but negotiators are hoping to make significant progress on a long list of items at these talks. As always, diplomacy tends to proceed fitfully.

What role will the U.S. play?

Even though the Trump administration has vowed to withdraw from the Paris agreement, the United States can’t formally exit the climate talks until 2020. So the State Department is sending a small team of negotiators to discuss some of the details of the pact.