World leaders in Paris under the impressin that they have pledged important greenhouse gas emission limits. Photo: Miguel Medina/AFP/Getty Images

The most unintentionally revealing commentary on the Paris climate agreement came from National Review senior editor David Pryce-Jones. “I know next to nothing about the technicalities of the subject, but caught on television news bulletins great wafts of hot air,” he confessed. “It was highly enjoyable to hear President Obama claiming to be saving the planet that his foreign policy has done much to endanger … You don’t have to be a cynic to think that most countries, China and India in the lead, are never going to do anything that might harm their economic development, nor will rich countries commit economic suicide.” This was a real-time window into the conservative mind processing the Paris climate agreement, beginning from a point of frank incomprehension of (and lack of interest in) any specifics of the issue, and proceeding immediately to the conviction that the deal would fail.

Conservative economic thought is structurally different from liberal thought. Liberal support for expanded government is based entirely in practical expectation that new programs can deliver concrete results — cleaner air, healthier children, higher wages for low-income workers, and so on. Conservative antipathy to expanded government is based ultimately on philosophical opposition. For that reason, data can change liberal economic thinking in a way it can’t change conservative economic thinking. Liberals would abandon, say, new environmental regulations if evidence persuaded them the program was not actually improving the environment, because bigger government is merely the means to an end. No evidence could persuade conservatives to support new environmental regulations, because conservatives consider small government a worthy end for itself. (As Milton Friedman once put it, “Freedom in economic arrangements is itself a component of freedom broadly understood, so economic freedom is an end in itself.”)

Most conservative energy on climate change over the last quarter-century has gone into questioning the validity of climate science. Conservative intellectuals have invested enough of their reputations into this form of scientific kookery that it cannot be easily abandoned. Instead, as the evidence for anthropogenic global warming grows ever more certain, and the political costs for Republican presidential candidates of openly questioning science rise, conservatives have shifted their emphasis from denying the science to denying the possibility that policy can change it. A National Review editorial last year dismissed the notion of an international agreement to limit climate change as a metaphysical impossibility, on the grounds that reducing coal usage in one place would axiomatically increase it elsewhere. As The Wall Street Journal editorial page asserts, “If climate change really does imperil the Earth, and we doubt it does, nothing coming out of a gaggle of governments and the United Nations will save it.” Having begun with their conclusion, conservative are now reasoning backward through their premises.

Accordingly, a new data point has taken hold on the right and quickly blossomed. One study by MIT finds that the Paris agreement would reduce the global temperature increase by a mere 0.2 degrees by 2100. The entire right-wing media has eagerly circulated the finding. “Current analysis by researchers at the Massachusetts Institute of Technology — not exactly a nest of fossil-fuel conservatism — suggests that the emissions cuts being agreed to in Paris would reduce that estimated warming by as little as 0.0°C or by as much as 0.2°C,” announces a National Review editorial, thrilled to have an empirical basis for the conclusion it previously asserted as an a priori truth. The same study has been recirculated by places like the Daily Caller, Fox News, and elsewhere. Rich Lowry, writing in the New York Post, reports, “The best estimates are that, accepting the premises of the consensus, the deal will reduce warming 0.0 to 0.2 degrees Celsius.”

In fact, this study is just one estimate, not estimates plural. There are many other studies, and while Lowry’s column does not reveal what process he used to deem the MIT study “the best,” we can probably guess that it has something to do with MIT being the one that supports his preferred conclusion. In fact, the MIT study does not produce the conclusion its gloating conservative publicists claim on its behalf.

Most analyses of the Paris agreement find that it would bring temperature increases somewhere in the range of halfway between business as usual and hitting the two-degree threshold. Here is a survey comparing the various estimates of Paris. This chart looks at various estimates of the resulting global-emissions level if all of the pledges (called Intended Nationally Determined Contributions, or INDCs) are implemented by 2025 and 2030. The ballyhooed MIT study is the light-gray line:

The MIT study comes out right in the middle. So MIT’s conclusion of emissions levels over the next 15 years is right in line with other estimates that assume Paris will do a great deal to limit climate change.

So why does MIT find such a small difference? Because, unlike most studies, it assumes that after the current round of pledges is carried out, no further action will take place. Other studies assume that most countries will continue to transition to green energy sources. So, while the MIT study yields similar results to others over the next 15 years, it diverges dramatically over the 70 years that follow. That’s the main reason why it gets such a small effect by 2100. As John Reilly, an author of the MIT study, told me over email, “I don’t agree with the idea that this indicates failure.” It merely demonstrates that the pledges at Paris will have to be followed up with continued action.

Now, you might wonder why conservatives have invested so much in a projection of political decisions that will all be made decades into the future. You might expect conservatives to put less weight in assumptions about the very distant future than they invest in measurements about near-term behavior. Instead they have rested their case on a political assumption the Paris pledges will be carried out quickly, but no other emissions reductions will take place for the next seven decades.

It is true, as conservatives gleefully shout, that the Paris agreement uses voluntary pledges rather than mandatory ones. But the distinction matters very little — since countries are sovereign, “mandatory” agreements have no world police to enforce them. Conservatives objected to previous climate deals precisely because their “mandatory” character presented an unacceptably onerous burden. Now the absence of that unacceptable feature makes the new agreement worthless.

The events leading up to and including Paris are completely consistent with the optimistic hypothesis, and deeply inconsistent with the negative one. The major emitters have implemented dramatic policy changes — a sweeping array of greenhouse-gas regulations in the United States, massive green-energy support in China and India. China appears to have already reached peak coal, and its energy intensity has fallen, allowing it to provide more energy to its people without polluting more. There is no plausible explanation for all of these policies and results except that these countries actually want to reduce global greenhouse-gas emissions and are at least willing to try concerted international action to accomplish that.

It is also certainly possible that global willpower to reduce emissions will weaken, or collapse entirely. Future events cannot be proven. Only rigid dogma like American conservatism (or, for that matter, Marxism) gives its adherents a mortal certainty about the fate of government policy that a liberal cannot match, and should not want to.