On Monday, the US filed paperwork that will begin the process of leaving the Paris climate agreement. Withdrawal will take final effect on November 4, 2020, one day after the next US presidential election.

To a great extent, the future of the agreement depends on the outcome of that election. Even now, negotiators are scrambling to make a plan for the possibility of a second Trump term.

But some amount of damage has already been done. It was done the minute Trump announced his intent to leave the agreement and began rolling back Obama’s climate regulations. This makes twice a Democratic president signed an international climate agreement and a Republican subsequently reneged (the first was the Kyoto Protocol, signed by Clinton in 1997 but never ratified by Bush). Even if a Democrat wins in 2020 and rejoins the agreement, who could trust that the commitment will last beyond 2024?

With so much riding on the next election, no one has quite tallied up the damage done by the abdication of US climate leadership. But there’s reason to believe it is substantial. In fact, there a reasons to believe that the Paris agreement is in bad shape, that in the 2020s it could break down or even fall apart entirely.

Those are the gloomy possibilities raised by Noah Sachs, an environmental law professor at the Richmond School of Law, in a new paper in Ecology Law Quarterly. He says a “downward spiral of dissent, dysfunction, and disengagement” is just as plausible as the optimistic story of ambition ratcheting perpetually upward.

Sachs, generally a believer in international agreements, views this as a bad thing, with untold ecological consequences. But he worries that people are not taking these more pessimistic possibilities seriously. So, with this paper in hand, let’s take a cold, hard look at the state of Paris. We’ll start with a little bit of background, for context.

The central dilemma of international climate politics

Climate change is a collective-action problem, and like all such problems, it is incredibly difficult to solve.

The costs of ambitious climate policies are borne in the present. They harm specific, powerful constituencies and are traceable back to individual politicians. By contrast, the climate benefits of those policies are diffuse, spanning over decades and continents. In situations like that, there is strong incentive to free-ride, to make the minimum contribution and rely on others to take up the slack. It’s a dilemma.

Many optimistic analysts point out that the cost-benefit calculus on climate action has changed in recent years. Clean energy is now cheaper than dirty energy in many circumstances. Many climate policies pay off in the near term in jobs, economic growth, or reductions in local air and water pollutants, even putting aside their climate-specific benefits. In short, many carbon-reducing policies are things it makes sense for countries to do anyway, for reasons beyond saving the world from climate change.

All of that is true, as far as it goes, but it does not go far enough. The IPCC says that, to get on a trajectory to limit the rise in global average temperature to 1.5 degrees Celsius, or even 2 degrees — the world’s shared targets — the global economy needs to rapidly reduce carbon emissions, hitting 50 percent less by 2030 and net-zero carbon by 2050. (After that, it will need to go carbon negative.)

The changes required to hit those targets are gargantuan and rapid, much bigger and faster than what national governments would do purely based on self-interest, especially given the inertia of the status quo. Some force or mechanism is needed to accelerate things, to push all countries farther, faster.

That’s what international climate negotiators, working through the UN Framework Convention on Climate Change (UNFCCC), sought for decades and decades: a way to collectively bind the world’s countries to ambitious emission-reduction commitments.

But it proved an exercise in futility. Harmonizing the interests of 192 countries and securing their unanimous consent for legally enforceable emission reduction targets is a puzzle beyond the ability of mere mortals to solve. 1997’s Kyoto Protocol, which at least would have entailed such commitments on the part of developed nations, was never ratified by the US and its targets weren’t met by those that did ratify. The search for a Kyoto successor failed as well, most notably in Copenhagen in 2009. The UNFCCC process was in danger of falling apart entirely.

Paris was a new solution to the dilemma

The Paris climate agreement of 2015 was a new approach. Rather than continue the quest for legally binding targets, it simply asked countries to submit voluntary commitments, or nationally determined contributions (NDCs). These NDCs are not binding, but countries who submit them agree to track their progress and report on it every five years, in regular “stocktakes,” beginning in 2023.

The idea behind the agreement is to get every country on record that it is at least getting started on the work of reducing emissions. The only way to do that, to bring countries out of their defensive crouches, is to forego penalties or enforcement mechanisms. Without that threat, it was thought, countries will be more open about what they’re willing to do. If nothing else, it would at least produce a clear measure of global ambition. (I described the logic of Paris in greater detail here.)

With every country on record behind tangible commitments and transparent about their progress, the architects of the agreement hoped that peer pressure would kick in. Countries wouldn’t want to put forward obviously weak targets, or underperform on the targets they did put forward, with everyone watching.

As countries succeeded on their modest targets, received international approbation for it, and got comfortable taking action, the thinking went, they would ratchet up their ambitions. And in doing so, they would encourage one another, setting off a self-reinforcing cycle of escalation.

Unfortunately, events since the signing of the agreement have not done much to support what Sachs calls the “upward spiral” theory.

The US bailed on Paris and may never be trusted again

First, of course, is Trump’s announced withdrawal from the agreement. That prompted a bunch of talk about how state and cities would rise to fill the gap. There was speculation that the US being gone would unleash other countries’ pent-up ambition to take greater climate action. There was even talk that the Paris agreement’s 187 remaining signatories were better off without the US.

But a lot of that commentary had the tenor of whistling past the graveyard. The treaty’s very nature was shaped around Washington’s requirements. US participation was considered crucial because it signaled that the treaty was universal and that the largest emitters would be role models — but it could not be binding, because that would require the consent of the US Senate, which was not forthcoming.

Now Trump has made clear that the US doesn’t intend to act, and further, that it plans to play a spoiler role in ongoing negotiations. If the US rejoins Paris in 2021 with a Democratic president, it will be welcomed with open arms, but that in itself will demonstrate that there is no penalty for flouting the treaty. And everyone will know that a Democratic president is going to be constrained by Congress from taking ambitious action and could well be out again in four years, with policy flailing in another direction. “Even if Trump is booted out of office in 2020,” Sachs told me, “other countries will not know whether they can trust US climate policies for more than one four-year election cycle.”

If Trump is reelected, the treaty is likely doomed. The rest of the world simply won’t continue ratcheting up its ambitions and taking on costs while the US pursues a course of climate unilateralism. But even if he isn’t, the absence of US climate leadership, which is now effectively a permanent condition, will deprive the agreements of one of its central engines.

Countries aren’t even doing what they said they would do in Paris

Second, there’s the simple fact that most countries are not on target to meet even the modest commitments they made in Paris. Writes Sachs of countries’ nationally determined contributions:

Evidence of NDCs’ shortfalls is accumulating. According to the latest annual assessment of progress produced by the Dutch Environmental Assessment Agency, only seven of twenty-five parties analyzed are on track, with implemented policies, to achieve their NDCs. For the European Union and for Mexico, the achievement of 2030 targets is uncertain with implemented policies. For another sixteen states, the Agency was confident that the parties would not meet their NDCs unless they adopted additional [greenhouse gas] control measures.

Successfully fulfilling a pledge does not necessarily indicate climate leadership; NDCs can be set at unambitious levels to begin with.

The Climate Action Tracker has calculated that the initial pledges, if fully implemented, would have led to global warming of between 2.5 and 3.8 degrees Celsius. But the trajectory of current policy leads to 2.5 to 4.4 degrees — an outcome all parties agree would be devastating.

There’s been some whistling past the graveyard about this as well, with commentators arguing that since NDCs are voluntary and based on national considerations, they won’t be affected by the failure of other parties to meet their targets. But Sachs is skeptical “that parties will remain unperturbed in the face of the failures of other parties.” After all, he says, “cooperative environmental regimes can be sustained only if parties perceive that other parties are making appropriate sacrifices.”

The failure of large economies to meet their targets is going to revive age-old arguments about who is doing their fair share and who is obligated to do more. And it will cast a shadow over the submission of new pledges in the 2020s. What will it matter if countries ratchet up their targets if they aren’t even meeting their current ones?

The scale of action needed has become daunting

If the world had begun gradually phasing out carbon emissions several decades ago, a gentle glide path toward carbon neutrality would have been plausible. But even as scientists have raised more and more urgent alarms, there’s been virtually nothing but delay; now, the amount of action needed is radical.

The gap between what has been promised and what is being done will only grow. The UN Environment Program (UNEP) calculates in its annual “emissions gap” report that, just in the 2020s, the difference between what countries have pledged and what’s necessary to limit warming to 2 degrees is 13 to 15 billion tons of carbon dioxide equivalent. By way of comparison, light-duty vehicles in the US emit about a billion tons of CO2e a year. So just think of the US auto sector ... 15 times over.

To bridge the gap, all countries will need to reduce carbon emissions between 5 and 8 percent a year, something no country has ever achieved, and do it through the end of the century. That will involve, among other things, one-third of all known oil reserves and 80 percent of known coal reserves being left in the ground.

Closing the gap will require rapid, costly efforts, and the Paris agreement has no way to allocate those efforts, ensure that any given party is doing its fair share, or penalize countries that act counter to the goal. Meanwhile, countries in Europe that are actually on target are going to watch in the 2020s as the 1,200 coal plants now under construction or in the permitting phase across emerging economies go into operation, rendering a 2 degrees limit impossible.

The majority of Paris parties are emerging economies and, almost without exception, they have submitted NDCs that would allow them to continue increasing their emissions through 2030 (albeit more slowly than baseline). On the current trajectory, in 2030, 45 percent of global emissions will come from countries whose emissions are still rising.

“With so many governments committed to increasing their [greenhouse gas] emissions through 2030 and beyond,” Sachs writes, “the stage is set for the 2020s to be a decade in which the scale of necessary reductions will simply overwhelm governments’ willingness or ability to achieve them.”

Climate finance is falling short and as contentious as ever

In the 2009 Copenhagen accord, developed nations pledged to direct $100 billion annually in public and private resources to financing climate change mitigation and adaptation efforts in the developing world, helping poorer countries to clean up.

Progress has been slow, to say the least. Since then, countries have pledged $10.3 billion to the Green Climate Fund, which was set up by the UNFCCC to direct climate finance to developing nations. They have actually transferred about $3.5 billion. And Trump announced that the US wouldn’t be making any further contributions. Nothing like $100 billion a year is anywhere on the horizon.

When evaluations of progress come out in the 2020s, emerging economies are going to see wealthier nations failing to meet their already inadequate pledges and failing to marshal anything close to the funding they have promised. “In the absence of that promised funding,” Sachs writes, “developing countries may refuse to make emissions reductions pledges commensurate with the Paris Agreement temperature goal.”

The whole peer pressure thing might not work out

The core of Sachs’s argument is that what he calls the “peer pressure proposition” (PPP) doesn’t hold up to a ton of scrutiny. As hopeful international negotiators have discovered again and again throughout history, domestic political considerations are primary. There are very, very few situations in which international opinion can override them.

There are some historical examples, like human rights, where there is broad international agreement, clear red lines that can’t be crossed, and real economic threat from sanctions or boycotts. (Even there, collective-action problems loom.) But climate change isn’t well-suited to that kind of thing. There are no clear red lines, no agreed-upon measures of who should be doing what and how much emitting is too much. And it is difficult to sanction countries for producing products that the sanctioning countries are consuming.

The peer pressure argument also seems to presume that emission reductions will get easier over time as technology gets cheaper, leading to a cycle of success and mutual inspiration. Yet that is optimistic. No natural rate of technology substitution, even assuming the best possible cost projections, will be fast enough to meet the 2 degree target. “Growth in global GDP and global population will likely swamp any reduction in carbon intensity per unit of GDP that stems from technology improvements,” Sachs writes.

And even if some technologies make some emission reductions cheaper in some regions, Sachs argues, “the assumption does not hold as a bankable general proposition for the world.” Ultimately, to succeed, the clean-energy transition must be planned and accelerated by policymakers, and right now that doesn’t look too hopeful: climate-denying politicians are finding success not only in the US, but in places like Australia and Brazil, where new president Jair Bolsonaro is almost single-handedly threatening to render 2 degrees impossible by burning up the rainforests.

“Economic and technological changes do not automatically favor greater commitments by Paris Agreement parties,” Sachs writes. “They may, or they may not.”

Finally, the Paris agreement doesn’t even contain many mechanisms to actually call out and shame countries who shirk responsibilities or fail to meet targets. And there are plenty of historical examples of treaties premised on naming and shaming that never triggered the hoped-for upward spiral.

Paris could break down or break up

Sachs sketches out two possible scenarios for Paris, breakdown or breakup.

Commitments will need to rise rapidly in the 2020s, but “there is no definition for appropriate ‘ambition’ in the Agreement,” Sachs writes. “There is no official body to determine which countries could commit to greater reductions beyond those named in their NDCs, and even if there were, such determinations would devolve in controversies over equity and historic responsibility.”

The agreement contains no mechanism for resolving the inevitable controversies over who is doing enough, and no real way to call out or penalize those who aren’t. In the absence of any tools to leverage national decisions, those decisions will be made on domestic considerations.

Breakdown happens if the failure of large economies to meet their targets causes rising acrimony and other countries make minimal pledges or slow-walk their own goals, leading to a “low-level equilibrium” in which NDCs remain static or rise only incrementally. Or countries might begin to withdraw their NDCs and submit less ambitious ones. The Paris agreement is generally considered by scholars to contain a one-way ratchet, allowing only for increases in NDCs, but without any mechanism to enforce that norm, it may hold only as long as it takes one big country to violate it.

In this scenario, Paris doesn’t fall apart, it remains the central forum for international climate cooperation, but it simply sputters, remaining notional and inadequate.

Or, breakdown could lead to breakup. That could happen if all the above trends accelerate, “persistent unbridgeable conflicts” that were papered over by Paris make further cooperation impossible, and countries begin pulling out. “As free-riding becomes evident in the face of increasingly severe climate impacts,” Sachs warns, “committed states may conclude that they are being duped.” They may start looking for ways out of Paris, opting for smaller agreements with groups of countries willing to act.

And of course exogenous events could intervene and accelerate a breakup. There could be a war, a global economic recession, or a series of climate-driven disasters that overwhelm the international system. “History shows that prolonged environmental scarcity and mass migrations promote authoritarianism and international conflict,” Sachs told me, “not a deeper spirit of generosity toward global environmental goals.”

Paris is not to blame for the outcomes of Paris

As gloomy as these warnings are, it’s important not to get too tangled up in thinking about the Paris agreement’s specific flaws, or what some other form of international agreement might have done better. The fact is, any international agreement (particularly a voluntary one like Paris) is more a reflection of aggregate national wills than a driver of them. An international treaty can capture and formalize what nations are willing to do, make it easier for them to coordinate, but it cannot generate national political will where there is none.

And when it comes to a large-scale collective action problem like climate change, national political will is tough to come by.

“I do not contend that any specific language in the Paris Agreement will cause Breakdown or Breakup, or that tweaks to the language could avoid a downward spiral,” Sachs writes. “Rather, the destabilizing factors are exogenous to the Agreement and reflect the strategic interests of major powers. The problem is not the treaty’s language. It is that climate change, by its very nature, creates thorny, intractable incentives toward non-cooperation and free-riding.”

The hope that an international treaty could counterbalance those incentives was always somewhat forlorn. “In an anarchic international system with no hegemon and no sovereign enforcement power, it is difficult to bring nations together in consensus and then sustain cooperation over time,” Sachs writes. That is more true of climate change than of almost any other problem.

Sachs still thinks it is better to have Paris than not to have it. “It facilitates international cooperation,” he told me. “It has regular review conferences, requires submissions of NDCs on a defined timetable, and requires submission of national emissions inventories.” What it cannot do, he said, is “command any particular result.”

It is not impossible that Paris could succeed, but that, too, would be a result of exogenous factors — cheaper than expected clean technology, a Democratic wave election in 2020, or a civil-society movement capable of mobilizing large-scale public pressure on politicians.

Ultimately, nations will do what they have the national political will to do. The Paris agreement reflects, but cannot change, the fact that collective will to address climate change remains sorely lacking.