Last year, on November 7 in Marrakech, Morocco, representatives of the world’s governments gathered to discuss their plans for implementing the Paris Agreement on climate change. The conference was overshadowed, however, by a momentous event on the second day: Donald Trump was elected president of the United States.

It’s been a year, and it’s time for diplomats to gather again for  the 23rd “conference of parties” meeting under the UN’s Framework Convention on Climate Change,  otherwise known as COP23.  This year’s gathering will be held in Bonn, Germany; Fiji, an island nation with much at risk, will be serving as master of ceremonies.

COP 21, in 2015, saw the Paris Agreement take shape. It was the first global effort to reduce emissions that all of the world’s major polluters — including, importantly, both China and the US — agreed to get behind. One year later, COP 22 coincided with the election of Donald Trump, the man who promised to pull the US out of that agreement.

A year later, he has made good on his promise — sort of. As we noted in June, the US cannot formally leave the agreement until November 2020, the same month that Trump will stand for reelection. The US has maintained that it plans to quit the Paris Agreement while also making ambiguous sounds about hoping to cut a “better deal.”

Meanwhile, the rest of the world has worked to cut its emissions — and, according to the World Resources Institute, many countries have already seen their emissions peak and begin to fall. Nicaragua, which had previously refused to sign onto the deal in protest, has now done so in solidarity with countries affected by climate change, leaving just the US and civil war-torn Syria as the only countries not participating in the deal.

The greatest challenge facing the Paris Agreement is that, in order for it to make a difference, countries will have to continue to submit more and more ambitious plans for cutting emissions, and will have to stick to them.

That becomes a far harder ask, particularly for poorer nations, when one of the world’s richest nations and one of the highest emitters per-capita — the US — is blowing off the process entirely. Nonetheless, the majority of the world seems committed to keeping climate negotiations moving. The question is whether they’ll be able to do enough, fast enough, and whether they can get past a series of hurdles COP 23 presents.

Here’s what we’ll be watching in Bonn

What do the talks hope to achieve?

The task of filling in the Paris Agreement’s blank spots tops the agenda. Despite the fact that most world leaders signed on over the past two years, the majority of the Paris Agreement still needs to be written, and the details of what it will say must be hammered out. In Bonn, negotiations need to work toward writing rules that will push countries to make more ambitious pledges toward addressing climate change every few years. They’ll also need to figure out how the UN will be able to tell if a country is keeping its promise.

This “rulebook” has to come together by next year’s conference, in 2018. That means negotiators will need to leave Bonn in two weeks having taken significant steps toward writing it.

Poor nations also are continuing to urge wealthy nations to put more money, and promises of assistance, on the table. With Fiji holding the gavel, the hope is that negotiators will focus more on helping countries to prepare, and to adapt to the effects that many are already experiencing. In the run-up to this year’s COP, Fiji is calling for countries to submit more ambitious plans for cutting their emissions. (These plans — called “nationally determined contributions,” or NDCs — are voluntarily, and countries are not formally punished if they break their promises.)

What will the US’s role be?

The US will be sending mixed messages in Bonn.

On the one hand, The New York Times reports that the Trump administration is sponsoring a presentation by representatives of US-based coal, liquefied natural gas  companies at the talks to, implausibly, “promote coal, natural gas and nuclear energy as an answer to climate change.” Fossil fuel companies and other dirty industries have played a prominent role in past year’s talks and are expected to do so again, lobbying diplomats to leave some room for dirty fuels in their nation’s climate futures. This time, they’ll have help from the White House.

Trump’s diplomats, meanwhile, are expected to play a more sensible role at the summit, and one that is largely at odds with the administration’s rhetoric. Secretary of State Rex Tillerson will not be present, and the climate change-skeptical EPA chief Scott Pruitt is unlikely to turn up either, though his schedule is not public. The tiny US delegation will instead by lead by undersecretary of state Tom Shannon, an Obama appointee who has continued into the Trump administration.

Ultimately, Shannon and his team will likely keep a low profile. If Trump decides to make good on his pledge to “renegotiate” the climate deal — widely interpreted to mean that the US would replace its initial NDC with something less ambitious — Shannon and his team likely won’t be the ones to do it.

Who will lead the talks?

With the US stepping away from the table, there is something of a power vacuum. The US’s leadership was effective because it was a major polluter that was willing to change. China now occupies a similar role, but, as many have pointed out, its efforts to develop infrastructure around the globe — the “One Belt One Road” project — will generate a tremendous amount of pollution, and seem to be divorced from the country’s efforts to clean up its act at home. But Xi Jinping wants to be seen as the heir to America’s ceded ambition; his negotiators may attempt to put some meat on the bones of his promises about “green development” abroad.

Meanwhile, Europe continues to play a de-facto leadership role because of its relative progress in, and earlier start to, cutting emissions. But activists are calling on European leaders to up their ambition as well, given their significant head start. This could include taking steps such as transitioning to 100 percent renewable energy and ditching subsidies for dirty fuels, including coal.

Given the unrelenting pace of climate change, does this even matter?

2017 was a year in which the effects of climate change, and the future they portend, came starkly into focus. Rogue storms and wildfires in Europe and the US, disastrous flooding in South Asia, drought in Africa, a hurricane season that demolished entire island nations, and the continued melting of the planet’s polar caps illustrated that climate change is not an eventuality that world leaders must plan for, it is a threat they must confront in the present, before it gets worse. Greenhouse gas levels, meanwhile, continue to reach new heights.

Global emissions will need to peak by 2020, and reach net zero by 2050, for the planet to have a shot at containing warming to 2 degrees Celsius, the Paris Agreement’s upper limit. Current NDCs aren’t enough to do that, according to a new UN report — if countries do not up their ambition, we are on track for something closer to 3 degrees Celsius by 2100.

That all means that COP 23 is critical. It will show whether, in the face of the US bailing, the rest of the world will be able to adequately address climate change. The symbolic importance of Fiji — the first nation to see a village relocate because of sea level rise — serving as president of the COP will drive that message home.

But the US’s decision to quit could prompt infighting between the nearly 200 countries who remain in the deal. The process of writing the agreement’s rulebook could serve to further highlight those differences.

It’s been an open question since Trump was elected whether the US would sink the Paris Agreement. The US has already scuttled one climate deal, the Kyoto Protocol, by refusing to sign on. If the same thing plays out again, it could prove truly disastrous for many developing countries. So far, the international community has touted its commitment to maintaining “momentum” and “unity,” but COP 23 will give us a sense of the strength of those commitments by presenting some of the greatest challenges to them yet.