The latest round of United Nations climate negotiations, COP24, are well underway, and seem unlikely to end Friday as scheduled. Somewhat oddly, the meeting is taking place in Katowice, a small city in Poland that was built on coal mining. Coal still provides 80 percent of Poland’s power and seems to be the visual theme of the event. (Like I said, odd.)

This is the most significant meeting of the parties to the Paris climate agreement since that accord was hammered out in 2015. Though the agreement doesn’t technically go into effect until 2020, the Katowice meetings are meant to encourage early ambition and serve as an informal “stocktake,” a check-in with how countries are doing relative to their upcoming pledges.

As you may have heard, a few significant things have happened in the US since 2015. Among them, Donald Trump was elected president and pledged to withdraw from the Paris agreement. The US cannot formally withdraw until November 5, 2020, just days after the next presidential election, so it’s still a somewhat theoretical threat. Still, it has been enough to affect the course of events.

But how much? How well has the Paris process withstood Trump so far? Among the many other more concrete issues discussed in Katowice, that is sure to be at the top of everyone’s mind.

A newly published paper can help us wrap our head around Trump’s damage: “The Paris Climate Agreement Vs. The Trump Effect,” by Joseph Curtin at the Institute of International and European Affairs (IIEA), a Dublin-based climate policy think tank.

But before we dig in the details, let’s recall why the Paris agreement is uniquely vulnerable to Trump’s skullduggery.

The Paris agreement relies on trust and leadership

The Paris agreement marked a new chapter in international climate negotiations — a sharp break from the past. For decades, the parties to the United Nations Framework Convention on Climate Change, a treaty adopted in 1992, had struggled to develop a legally binding agreement, with formal sanctions for failure.

That never happened, for many reasons, most notably the requirement that any such agreement garner unanimity among almost 200 countries, while the US, among others, was inalterably opposed.

The Paris agreement works differently. I have told that story in detail, but the capsule version is simple: instead of relying on legal or economic sanctions, Paris harnesses the power of transparency and peer pressure.

Each country comes up with its own emissions-reduction pledge, its own “Nationally Determined Contribution,” or NDC. (There are 165 NDCs so far — you can see a list and a map here.) Then, on a rolling five-year basis, there are formal “stocktakes,” in which countries report on their progress.

There’s no sanction for failing to hit your targets. You just have to honestly tell the rest of the world how you’re doing. If you fail to achieve your publicly proclaimed goals, you will be embarrassed and suffer reputational damage.

The idea behind the agreement is that making NDCs voluntary, with no risk of penalties, frees up countries to be less defensive — to just get started. As they do, they will learn and share, prompting a self-reinforcing cycle of rising ambition, driven by bragging rights and encouragement rather than shame and sanction.

“It created a new type of institutional arrangement designed to generate momentum for innovation, deployment, learning by doing, new norm creation and general positive encouragement,” Curtin writes, “but without punitive enforcement mechanisms for non-compliance.”

For obvious reasons, an arrangement like this relies on trust and good faith. Countries act because they believe others are going to act. But if a major country, responsible for almost 15 percent of the world’s greenhouse gas emissions, craps all over the process and bails out ... well, that hurts.

How much?

Three ways the Trump effect is hurting the Paris process

First, let’s acknowledge that it’s still early days. We’re talking about how a withdrawal that hasn’t happened yet is affecting an agreement that hasn’t gone into effect yet. In terms of the formal legal mechanisms of the Paris agreement, nothing has happened, so obviously Trump has had no effect.

Nonetheless, these years leading up to the formal launch of the treaty are incredibly important for setting expectations and ramping up early ambition. Trump is messing with both.

Curtin breaks down Trump’s effect into three buckets:

1) Trump’s regulatory rollbacks have shifted investment incentives.

Trump has started rolling back every Obama climate regulation he and his people can get their hands on, including the Clean Power Plan, Obama’s program to reduce emissions from existing power plants.

Many of those rollbacks will go through years of rulemaking and court battles before taking effect. (In concrete legal terms, there’s been very little actual deregulation yet.) But one thing Trump and his EPA have guaranteed is a long stretch of regulatory uncertainty and legal chaos. Even if and when his efforts fail in specific cases, he will still have successfully delayed implementation of a whole range of regulations.

While there are big shifts happening in the energy sector that Trump can’t hope to stop, he can, at the margins, shift investment incentives toward the old (fossil fuels) and away from the new (clean energy).

Right now, activists and shareholders are trying to convince the financial world to pay heed to the danger of “stranded carbon,” i.e., carbon-intensive investments, like coal plants, that will be rendered uneconomic by climate policy. They want companies to disclose that “carbon risk,” and to act on it.

But the threat is premised on the idea that carbon policy will happen. To the extent that the US signals it’s wide open for fossil fuel investments, it will take the edge off that risk.

Curtin writes:

Analysis has found that a sharp flight from the dirtiest fossil fuels investments was reversed in 2017, and that American banks led a race back into unconventional energy. For example, JPMorgan Chase quadrupled its tar sands investments. In the coal sector, among 36 banks surveyed in the same study, investment increased by 6% in 2017 after a 38% drop in 2016. The other side of the same coin is that, according to the IEA, investment in renewables declined by 7% in 2017. Its Executive Director, Dr Fatih Birol, ascribed this to the uncertainties created by politics.

In short, despite the fact that Trump’s rollbacks are more promises than realities today, the US government can affect energy markets, and give fossil fuels a small measure of respite, merely with its promises.

2) Trump’s skullduggery offers other scofflaws political cover.

The Paris agreement relies on fairness. Everyone has to feel like everyone else, or at least most everyone else, is doing their part. Several countries have made even pledges that are contingent on other countries matching their ambition.

The near-unanimity of support for the agreement (and the flood of NDCs) left holdouts and renegades — of which international climate negotiations has always had its share — few places to hide.

Now that the US is out, though, all bets are off. Curtin writes:

In Australia, the Trump Effect was repeatedly cited to support abandoning legislation to deliver compliance with its Paris pledge. In Turkey, President Erdoğan announced he would not ratify the Paris Agreement, “after that step taken by America.” In Brazil, meanwhile, the newly-elected President, Jair Bolsonaro, tweeted an article defending Trump’s withdrawal the day after the decision, and has promised to follow President Trump by withdrawing Brazil from the Paris Agreement.

Brazil has also rescinded its offer to host climate negotiations next year.

It’s not just the holdouts, though. There is tension within every national government. Japan, Indonesia, Turkey, and South Korea have all lurched in a coal-friendly direction recently. Russia no doubt wants to sabotage Paris like everything else. Saudi Arabia still likes oil.

Even in China and India, which have stated that they will hold to their targets, developments are mixed and there are internal divisions.

When the US, the world’s second big emitter, drops out to make as much money as it can on fossil fuels while the world burns, it strengthens the hand of naysayers in every national government.

This weekend, G20 leaders released a joint communiqué in which they pledged to fight climate change. Only one country of 20 refused to sign: the US. That sends a message to every proto-Trump and mini-Trump the world over.

3) The erosion of trust poisons climate negotiations.

Very few countries are currently on a trajectory to meet their Paris targets. And Trump has likely put to rest the prospect of countries ramping up their pledges before 2020. Many countries will start the formal Paris process already behind.

And pushing them to move faster will be difficult when the US is out.

For one thing, Obama pledged $3 billion to the Green Climate Fund, which helps developing countries cope with climate change. The US has paid just $1 billion of that, and Trump is adamant that not another penny will be forthcoming. There have always been tensions around the fund — it is the main incentive for many poor developing countries to participate in the process at all — and its shortfall will throw sand in the gears of any discussion about boosting ambition.

Everything becomes more difficult when the US refuses to engage in good faith.

So, how should we add all this up, the full Trump effect?

“At a time when greater speed of decarbonisation is essential,” Curtin writes, “the Trump Effect has clearly applied a brake. On the other hand, it is a mistake to suggest that the Agreement is in crisis, or worse still, that all parties are failing to live up to their commitments.” There are, after all, still plenty of countries moving forward aggressively.

It’s bad, but it could be — and still may be — worse.

The true Trump effect can’t yet be calculated

There are three key points to add to the above analysis, to put it in perspective. Curtin provides the first two; I’ll add a third.

Point one: The proper comparison is not simply Trump’s effect to its absence. The proper comparison is Trump’s effect to what might have happened if the US were being led by a competent administration committed to addressing climate change. The US, led by Hillary Clinton, would be ramping up its own ambition and engaging in Katowice in good faith.

“The US, working in tandem with like-minded partners, could have created much higher political, diplomatic, financial, technological, trade, and moral barriers for defection,” Curtin writes.

That’s the real Trump effect — the distance from that counterfactual.

Point two: The reality is that Trump, on this as on everything else, is not de novo. He is simply the crude and extreme version of the Republican Party — the culmination of longstanding trends on the right.

And it’s the US right, specifically the Republican Party, that has had the true effect on international climate negotiations. Curtin summarizes the history:

The decision to withdraw [from Paris] cannot therefore be interpreted as an aberration — in fact, it is consistent with a pattern of Republican Administrations extending back nearly four decades. President Reagan famously declared open war on solar energy, and was determined to reverse as many environment regulations as possible in service of the drilling and mining lobbies. The George H. W. Bush Administration delayed the agreement of a climate treaty in the late 1980s, and at the 1992 Rio Earth Summit refused to commit to specific emissions reductions. A decade later George. W. Bush renounced the Kyoto Protocol. It is for these reasons that Paris is a non-binding Agreement, not a Treaty requiring ratification by the US Senate, and it is for these reason that it has a drawn-out withdrawal process — it was bent into a shape that fits the contours of domestic American politics.

The GOP is alone among major political parties in the world in rejecting mainstream climate science entirely. It has pledged itself openly to fossil fuels.

To the extent that a climate agreement requires Republican support, it won’t happen. That’s how it’s been from the beginning. The entire history of international climate negotiations has been “bent into a shape that fits the contours of domestic American politics.”

However big the Trump effect, it is only a fragment of the GOP effect, which is immeasurably larger.

And that’s why the 2020 presidential election won’t necessarily be the end of those effects, even if a Democrat wins. It has now become extremely clear to the entire world that any time the GOP gains control in America — which can obviously happen — all progress on international negotiations will be exploded.

Politically speaking, the US is a Jekyll and Hyde. Other countries don’t know what they’re going to get when they enter into agreements with it. Even when they don’t have power, Republicans can poison the trust that international agreements rely on.

Point three: That being said, it very much matters for the Paris agreement who is elected US president in 2020. It’s not clear that Paris could survive another four years of Trump and the US actively working to undermine climate policy and stimulate fossil fuel markets.

The Paris framework was designed to be resilient, to survive defections, but the US is an extremely large and influential defection. If it leaves for good, it will test the agreement’s strength dearly.

Some of your more hysterical US commentators (uh, me) reacted to Trump’s election by writing off Paris’s 2 degree climate target as a lost cause. It’s too early yet to say whether that was prescient or hyperbole. But I will say this: If Trump is reelected, Paris or no Paris, 2 degrees will be off the table and millions will suffer as a result.

That will be some Trump effect.