There's a radical idea at the heart of the big Paris climate accord that strikes many people as baffling. The deal is ... largely voluntary. That's right: None of the 195 countries that signed on are actually required to make emissions cuts.

Sure, every country is required to submit some sort of plan to address climate change. But the content is entirely up to the country. The plans can be ambitious (like Costa Rica's) or laughably weak (like Russia's) or somewhere in between (China's or America's). What's more, no country will be forced to take further actions, and no one gets penalized if they fail to live up to their promises. The only thing countries have to do, really, is report on their progress in transparent ways and submit new plans every five years.

It's a major gamble on the fate of the planet. The architects of this deal are essentially hoping that cooperation and peer pressure will encourage nations to ratchet up their plans and ambitions over time. With no guarantees.

But it's not a totally crazy idea, either. And to see why this might make sense, we have to take a trip through the history of global climate talks. For nearly 20 years, UN negotiators have been trying — and failing — to craft a legally binding global treaty that would require countries to make cuts. It was those depressing failures, and the insights that arose as a result, that ultimately led to the Paris deal. And that history is crucial for figuring out whether this new approach stands any chance of working.

Why past attempts at a legally binding climate treaty failed

Let's go back to the early 1990s, when MTV still aired music videos and world leaders (like George H.W. Bush) were just starting to realize we needed to tackle greenhouse gas emissions in order to avoid drastic global warming. The trickiest part would be coordinating efforts internationally, since no single country could solve the problem by itself.

At the time, there was a promising template for doing something like this. The world had just agreed to a global treaty in 1987 called the Montreal Protocol, which required all nations to phase out CFCs — a chemical used in refrigerators and air conditioners that was munching through our ozone layer.

The Montreal Protocol had a few key features. First, it imposed hard targets for how quickly CFC production should be phased out, based on input from scientists. Second, it was legally binding. The US Senate ratified the treaty in 1987, making it the law of the land. Third, it made special allowances for poorer countries, which were actually allowed to increase CFC use for a period of time before making reductions.

That treaty was a huge success, saving the ozone layer and preventing us all from getting toasted by harmful ultraviolet rays:

So, the thinking went, why not craft a climate treaty in the same way? Negotiators could set hard targets for countries to reduce greenhouse gases, based on what scientists thought necessary to avoid dangerous global warming. The treaty could be legally binding, so that no country could free-ride on the efforts of others. And, for fairness's sake, rich countries would take the lead in making cuts, since they were responsible for most of the CO2 already in the atmosphere. Poor countries would get leeway.

Enter the 1997 Kyoto Protocol, a treaty that split the world into developed ("Annex B") and developing ("non–Annex B") countries. Rich countries would adopt legally binding targets: The European Union, for instance, had to cut its emissions 8 percent by 2012. Developing countries like China and India would get a pass for the time being, since their per capita emissions were much lower and they were still growing.

The result ... was a total fiasco.

From the outset, the US Senate refused to ratify the treaty, with senators complaining that China didn't have to restrain its pollution at all and that US factories would just move overseas. George W. Bush formally withdrew from Kyoto in 2001. Later on, Canada failed to hit its targets and also withdrew, with no penalty.

Europe, Japan, and New Zealand did stay in the treaty, although it turned out to make little difference. In subsequent years, those poorer "non–Annex B" countries like China and India grew so fast and burned so much coal that global emissions soared, swamping the meager cuts rich countries made. In the chart below, it's hard to see that Kyoto had any impact whatsoever:

A couple of hard lessons emerged from this mess. First, reducing fossil fuel use was vastly more complicated and difficult than phasing out CFCs (which had a ready substitute available by 1987). Second, any future climate agreement absolutely had to include action from developing countries like China and India. There was no stopping climate change without them.

So at the Copenhagen talks in 2009, UN negotiators tried to craft a successor treaty to Kyoto that would require all countries, rich and poor, to make commitments. But that didn't work, either. Countries like China and India were willing to propose some actions, but they didn't want to submit to legally binding goals. What's more, they continued to insist that rich countries like the United States and Europe should bear most of the burden. (They had all gotten rich by burning coal; now it was India's turn.) Those talks ultimately concluded with nothing more than a vague resolution and acrimony.

How the Paris talks differed from those older, failed approaches

After the Copenhagen fiasco, policymakers began groping about for an alternative approach. One of the core insights, which had long been developed by political scientists like David Victor and Robert Keohane, was that the quest for a legally binding treaty was, in some ways, an obstacle to progress.

After all, no treaty is truly binding. There is no global SWAT team that will bang down your door if you don't sign on. (The United States and Canada dropped out of the Kyoto Protocol, and no one did a thing.) But on the flip side, adding too many legal requirements can make countries reluctant to join. If China thinks it will be held liable for its promises to boost clean energy, then it simply won't agree to very much.

So that's where the architecture for a new climate agreement was born, hashed out in conferences in Lima and then in Paris. Every country would start by submitting an entirely voluntary pledge for how it planned to address climate change. The content would be up to each individual government, rooted in its analysis of what it deemed politically practical and technologically feasible.

One upside here is that this approach ensured universal participation. Every country may as well submit something, since there was little downside. What's more, countries could feel more comfortable making ambitious plans. They don't have to stick with the absolute bare minimum for fear of failing and being sanctioned or held liable.

This approach also allowed countries to tailor their climate efforts to their own individual circumstances. China could focus on measures that curtailed air pollution in cities. India could focus on bringing solar power to villages that don't have electricity. The Obama administration could craft a short-term target based on its existing EPA authority — it didn't have to agree to a pledge that Congress wouldn't deliver on. None of these plans were imposed from on high by UN bureaucrats.

By late 2015, virtually every country in the world had submitted something:

The United States promised to cut its greenhouse gas emissions at least 26 percent, compared to 2005 levels, by 2025, through policies like the Clean Power Plan to decarbonize power plants.

The European Union pledged to cut emissions 40 percent below 1990 levels by 2030.

China vowed that its emissions would peak around 2030 and that it would get about 20 percent of its electricity from carbon-free sources by then.

India would continue to reduce its carbon intensity, or CO2 output per unit of economic activity, in line with historic levels (though overall emissions will grow).

These pledges, known as Intended Nationally Determined Contributions, would be the backbone of any future agreement.

In December 2015, negotiators met in Paris to craft an accord meant to give structure and momentum to the pledges. Under the deal, nations will be required to report their greenhouse gas emissions in a transparent way. They'll also have to return every five years to offer up new pledges. There are also some (non-binding) goals around climate financing for poor countries. As I've written, the idea is that cooperation and political persuasion can achieve what the quest for a binding treaty failed to do.

Because the actual legal requirements were so light, it was (relatively) straightforward for every country to agree to this deal. Because the pledges themselves are voluntary, the deal doesn't need to be ratified by the recalcitrant US Senate. So, for the first time, climate negotiators emerged from Paris with a deal that covered every single country, rich and poor. Finally, everyone was on the same page.

Will the Paris deal's voluntary approach actually work?

But it's not enough for everyone to be on the same page. A climate deal is only a success if it reduces the risk of dangerous climate change. Otherwise it's just puffery.

Right now we're not there. If you add up all the pledges that have been submitted so far, they add up to about 3°C of global warming — which is well above the 2°C mark that has long been considered unacceptably risky. And that's assuming everyone actually follows through, which they might not.

So the hope is countries will be motivated to voluntarily ratchet up their ambitions every five years. But we don't yet know if this will actually happen.

The case for optimism: If you want reason for hope, you can note that in the run-up to Paris, lots of countries really did appear to offer fresh initiatives and actions. China's pledge to get 20 percent of its electricity from clean sources by 2030 was new and a departure from business as usual. The Obama administration has been crafting new EPA rules on greenhouse gases with an eye toward these global talks. That suggests that countries really do respond to peer pressure and persuasion.

It also raises the possibility of a virtuous circle. Countries feel more confident acting if they won't be penalized for failure. That, in turn, encourages other countries to act, since they know they're not alone. And once countries start down the path of action, it becomes self-sustaining, as entrepreneurs and engineers find solutions that enable further action. Countries start pursuing wind or solar or nuclear and find new ways to bring down costs, enabling further action.

The other promising aspect of the Paris approach is that because it's not a single comprehensive treaty that tries to address all of climate change in one fell swoop, it allows side agreements and voluntary measures to bloom. The US and China reached a bilateral deal to collaborate on clean energy R&D and carbon capture pilot projects. India is allying with 120 other poor countries to bolster the market for solar. These sorts of efforts are harder to pull off when everything has to go through a legally binding UN treaty that needs to be agreed to by more than 190 countries. The hope is we'll see more of these.

The case for pessimism: But maybe this won't happen! Some experts, like Yale's William Nordhaus, see climate change as fundamentally a free-rider problem. Shifting away from fossil fuels is hard and expensive, and countries will be reluctant to incur heavy costs if the benefits will be dispersed around the world. Without some sort of external coercion, most countries aren't likely to step up their game and make the radical changes needed to keep us anywhere close to 2°C.

The cynical view on Paris, then, is that action will continue to be sluggish. Once the gleam of the conference has faded, the old divisions and backbiting will return. India will accuse rich countries like the United States and Europe of needing to do more, using that as an excuse to do less. The United States Congress will complain that China isn't doing enough. And so on.

(By the way, Nordhaus has argued that one way around the free-rider problem would be for a few major emitters like the US, China, and Europe to work among themselves to enact a carbon tax that encompasses imports and exports, thus forcing other countries to join over time. It's a clever idea, though seems like a political nonstarter right now.)

The case for waiting and seeing: Unfortunately, we probably won't know which view is right for years. As Michael Levi points out, the big test is what happens in 2020, when countries are supposed to review their pledges and submit new ones to the UN. Will governments ramp up their ambitions and offer genuinely new actions? Or will the virtuous circle theory prove hollow?

We also don't know yet what will happen if any country backslides in a major way. For instance, the Obama administration's pledge to cut US emissions largely depends on executive actions, which depend on the next president. What happens if Ted Cruz waltzes into office in 2017 and says the United States is abandoning its goals? Does that deflate efforts by other countries?

These are all genuine concerns! But they all revolve around the fundamental truth that the only way to solve climate change is for individual countries, particularly the largest emitters, to pass policies and adopt technologies that will reduce emissions. That, in turn, depends on politicians and engineers and scientists and activists and businesses. The lesson of the past 20 years is that UN negotiators have only a limited ability to shape this dynamic. They can nudge, but they can't demand. The Paris deal is the first climate accord that acknowledges and tries to work within that sobering reality.

Further reading:

Our explainer on what the Paris climate deal does

explainer Two academic papers that presaged the current thinking around climate deals: "The Regime Complex for Climate Change," by Robert Keohane and David Victor, and "Toward Effective International Cooperation on Climate Change," by Victor. (There are no doubt many others; feel free to send links.)

"The Regime Complex for Climate Change," "Toward Effective International Cooperation on Climate Change," In the New York Review of Books, William Nordhaus recently argued (implicitly) that the Paris deal doesn't address the free-rider problem. His essay is worth reading.

recently argued Back in 2008, Cass Sunstein wrote a concise essay on why the Montreal Protocol for CFCs succeeded while the Kyoto Protocol for climate failed, despite having similar architecture.