President Donald Trump’s advisers are reportedly having a fierce internal debate over whether the US should pull out of the Paris climate deal — the key international treaty to address global warming.

During the campaign, Trump promised to “cancel” the deal, and senior adviser Stephen Bannon wants him to follow through immediately, reports Coral Davenport of the New York Times. On the other side, she notes, Secretary of State Rex Tillerson and Ivanka Trump are urging Trump to keep the US in the treaty, fearing that an abrupt withdrawal would have “broad and damaging diplomatic ramifications.”

But there are a few policy nuances to this debate that are worth exploring. If Trump does decide to walk away from Paris, pay attention to how he does it — since that could influence whether countries like India or Brazil end up scaling back their own climate efforts in response. Conversely, if Trump sticks with Paris, that’s not necessarily a total victory for efforts to tackle global warming, since a lot depends on how seriously the US works to reduce its own emissions — and how the State Department approaches negotiations on the treaty’s future in the years ahead.

“There are important degrees here,” says Andrew Light, a former senior climate negotiator at the State Department who is now at the World Resources Institute. “The further they step away, the more likely it will have repercussions in other countries.” To make this a bit clearer, here are three big things to watch:

1) If Trump decides to leave the Paris deal, how does he do it, exactly?

President Trump Departs White House En Route To Newport News, Virginia Photo by Alex Wong/Getty Images
Is that a “bye Paris” or a “bye UNFCCC” wave?

Under the Paris climate deal, nearly every nation has put forward an individual pledge to curb greenhouse gas emissions. The US vowed to cut its emissions 26 to 28 percent below 2005 levels by 2025. China vowed to get 20 percent of its energy from low-carbon sources by 2030. And so on. Countries also agreed to meet regularly and review and strengthen their pledges, known as “nationally determined contributions” (NDCs).

But the Paris accord isn’t a legally binding treaty — it hasn’t been ratified by the Senate, and it’s effectively voluntary. So if Trump wanted, he has a few options for pulling out, each more drastic than the last.

One possibility would be for Trump to invoke the Paris accord’s formal withdrawal mechanisms, which would take four years to complete. Far more radically, the US could pull out of the underlying United Nations Framework Convention on Climate Change, which would take just one year to do and signal that the US is withdrawing from all international efforts on climate change.

Either option would be seismic. “If they pull out altogether,” Light says, “the chances increase that developing countries like Brazil or India back away from their own commitments and say, ‘Why should we bother doing this if the world’s biggest historical emitter is completely out of the game now?’”

That doesn’t mean other countries would exit the deal — China and India have their own reasons for acting on global warming — but a US withdrawal could well blunt the global momentum on climate action that has been building the past few years.

On top of that, if Trump opts for withdrawal, he’s likely to face all sorts of international condemnation and blowback. Europe, China, and other countries could threaten to withhold cooperation on issues the US cares about. Maybe Trump wouldn’t care. But it’s also possible, as Sen. Bob Corker (R-TN) hinted to the Times, that Trump will decide it’s smarter to just keep the US in the Paris deal. After all, the individual pledges are voluntary. There’s no concrete harm in hanging around. Why not?

2) If Trump sticks with Paris, does he just ignore the US pledges?

 (Shutterstock)
Trump wants to make coal great again, remember.

Okay, now imagine Trump decides to stay in the Paris accord. After all the inevitable puff pieces about Ivanka’s influence subside, there’s still the far more important question of whether the Trump administration would try to fulfill any of the US commitments under the deal.

Odds are, they wouldn’t. Trump has already vowed to repeal many of Obama’s climate policies, including the Clean Power Plan to curtail emissions from power plants as well as various regulations around methane leaks from oil and gas operations. If Trump rips those up, it will be extremely difficult for the US to cut emissions 26 percent by 2025, as promised. And if the Trump administration tries to revise and scale back the US targets under Paris, that could undermine the deal from within.

What’s more, a central part of the Paris deal involves the US pledging $ 3 billion in aid to poorer countries to help them expand clean energy and adapt to droughts, sea-level rise, and other ravages of global warming. The Obama administration already chipped in $ 1 billion. But Republicans in Congress and the Trump administration have insisted they have no intention of delivering the rest.

Some experts think that Trump abandoning US commitments on aid could be nearly as damaging to international climate efforts as withdrawing from Paris altogether. “For the developing countries, this will be a sign that America is unreliable and that the benefits of staying engaged in climate negotiations are fleeting,” writes David Victor, a political scientist with the University of California San Diego.

That said, Light thinks this outcome would still be less disruptive than total withdrawal: “Say Trump stayed in Paris, kept its nominal targets, but dismantled the Clean Power Plan. There’d still be enough action from states and cities that you could imagine the US ending up at the very low end of its emissions pledges. And that would still leave the possibility that the US could rebound [on climate action] after one term of Trump. So that doesn’t give nearly as much ammunition to other countries to say let’s ditch this whole thing.”

3) If Trump sticks with Paris, how might US negotiators shape future agreements?

The 2015 Paris accord was only a first step in the long, grinding process of dealing with climate change — and a woefully inadequate step at that. If you add up all the NDCs worldwide, they don’t come close to keeping us below 2°C of global warming. They add up to a severe 3°C or more, depending on which analysis you trust:

 (World Resources Institute)

The hope with the Paris accord was that these individual national pledges would be strengthened over time, as countries cooperated and pushed each other to increase their climate ambitions. So a key question here is what role Rex Tillerson and US climate negotiators might play in this ratcheting process.

For example: Over the next two years, negotiators are meeting at the UN to hash out rules around how to review individual country pledges and policies. This “transparency mechanism” could prove a contentious subject. The Bush and Obama administrations had long pushed for strict, uniform transparency standards. China and various developing nations, by contrast, have in the past preferred a “bifurcated” system that holds them to somewhat looser reporting requirements.

If Trump does stay in Paris, will the US try to hold China and other developing countries to the strictest transparency standards possible? And if so, how much leverage will the US really have here if we’re also reneging on our emissions targets and aid promises elsewhere? (Obviously, if the US leaves Paris entirely, it won’t have any leverage over transparency.)

This sounds like an obscure issue, but for many observers it’s critical. After all, climate change is a collective action problem. Countries are less likely to take the plunge and push for emissions cuts unless they know everyone else will jump with them. “To me, the essence of this agreement is what it can do to strengthen confidence that everyone’s doing their fair share, primarily through greater transparency,” says Elliot Diringer, executive vice president of the Center for Climate and Energy Solutions. “With greater confidence, everyone can do more. Weaker transparency rules would make it harder to strengthen confidence and ambition over time.”

Beyond transparency, the world’s nations are also supposed to formally take stock of their progress by 2018 and then submit new — and ideally stronger — NDCs by 2020. But this process of strengthening global pledges could get bogged down if the United States is falling far short of its targets because Trump dismantled US climate policies. It’s not hard to imagine India or China feeling less pressure to step up their efforts if the richest country on Earth is backsliding.

The basic point here is that the Paris climate deal isn’t guaranteed to succeed just because Trump sticks with the agreement. These nuances of what happens to a process that’s already well underway really do matter — and there are lots of ways the US could potentially weaken it from within.

Further reading: Our primer on how the Paris climate deal works.

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