Ever since climate change entered U.S. public consciousness — let’s date it to James Hansen’s 1988 testimony to Congress — one objection to national climate legislation has remained steady: It will hurt our country without benefiting the climate. If we raise the price of fossil-fuel energy, carbon-intensive industries will simply migrate to other countries, possibly even emitting more carbon there. We’ll hobble ourselves economically for no net reduction in carbon. “It’s called global warming, not American warming!” (A related argument is sometimes made about investing money in cleantech RD&D: Other countries will enjoy the benefits — the “spillover” effects — of our investments without any of the costs.)

This objection was the substance of the famed Byrd-Hagel Resolution, signed by 95 U.S. senators, which said that the U.S. would not ratify the Kyoto Protocol as long as developing countries were exempt from carbon targets. It has been a reliable go-to for those fighting off climate legislation ever since.

For reasons not entirely clear to me, Harvard law professor (and former head of Obama’s Office of Information and Regulatory Affairs) Cass Sunstein has rebranded this old chestnut the “sophisticated objection” to climate action. Now that science rejectionism has become the baseline position on climate in the GOP, I guess anything short of outright obscurantism counts as sophisticated.

Sunstein’s arguments against it (he believes the U.S. should act unilaterally on climate if necessary) are also fairly familiar: first, that American action is a necessary precursor to international action; second, that regulation spurs cleantech innovation; and third, that many actions we could take unilaterally already pass a cost-benefit analysis based on the widely accepted social cost of carbon.

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Over at National Review Online, Reihan Salam has rounded up (and written) some interesting responses to Sunstein. Kudos to Salam, by the way, for being the rare conservative to take climate seriously. I hope he prompts some internal NRO discussions.

The first is from Oren Cass (er, no relation to the other Cass), one of Mitt Romney’s top domestic policy advisers in the 2012 campaign. In it, he addresses Sunstein’s third argument. He says:

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This argument doesn’t answer the Sophisticated Objection, it ignores the Objection altogether. If carbon emissions actually had a quantifiable, linear, ton-by-ton cost then the Sophisticated Objection would make no sense because the value of action at home could be measured independent of what action was or was not taken abroad. If we gain the same benefit every time we reduce emissions by another ton, why would we care what China does? But of course, as Sunstein acknowledges by taking the Objection seriously in the first place, this is not how climate change works.

The entire premise of the Objection is that climate dynamics are extraordinarily non-linear and that the climate change threat is not susceptible to mitigation at the margin. The best science available today attempts to estimate the amount of warming associated with a given level of carbon in the atmosphere, and to determine the thresholds at which such warming is likely to trigger severe and irreversible effects on climate systems. On their current trajectory, global emissions blow through these thresholds; blowing through them by a little bit less does not have much value.

Cass is onto something important here. Many of the damages scientists fear most from climate change are nonlinear — that is, pressure on an biophysical system builds and builds until it “snaps” suddenly into a new steady state (“suddenly” relative to geological time, that is). Cass is right: If one of those “tipping points” is going to be triggered at, say, 550 parts per million of CO2 in the atmosphere, there’s no value at all in a policy that hits 560 instead of 580. If you tip, you tip; irreversible is irreversible.

But Cass also misses something important. If we knew that, say, 550 ppm was a tipping point, then yeah, we could judge climate policies by whether they exceed that target; any policy that falls short of it would be worthless. However, we don’t know where those thresholds are or how much carbon will trigger them. In the face of that uncertainty, all we have to go on are degrees of risk. We may not receive a standard unit of benefit for every ton of carbon emissions reduced, but we do, for every ton, reduce our risk by some increment. (More on the risk-management framework here and, at greater length, here.)

Cass is right that traditional cost-benefit is ill-suited to climate change, what with its large uncertainties and long-tail risks. But a full accounting of the uncertainties and risks involved suggests we need more aggressive action, not less.

Cass also has a response to Sunstein’s second argument, about innovation. Sunstein rather misleadingly uses “regulation” as a shorthand for innovation policy, but says little else about it. Needless to say, no one seriously involved in innovation policy thinks that regulation alone does the trick. For his part, Cass delivers the usual conservative cant that basic R&D money is good, but anything else — performance standards, deployment incentives, tax breaks, loans, what have you — is meddling with the holy market and destined to fail. This is bullshit, but it’s bullshit of long standing and I don’t feel like hashing it out here again.

Finally, Salam takes issue with Sunstein’s first argument, questioning “whether the moral authority of the U.S. is enough to persuade, for example, India or China to take a step that will prove economically damaging in the short-term, and perhaps in the long-term as well.”

This argument too has been oversimplified. If one thinks of climate policy as being coextensive with economic pain, then yes, it will be hard to persuade developing countries to show much ambition. But it is not coextensive with economic pain — there are immense benefits, not only in avoided climate change but in public health and well-being.

The fact is, the results of serious climate mitigation efforts are, like climate impacts, subject to a huge degree of uncertainty. At this point, almost all countries agree that horrendous danger is looming up behind them. They agree on the need to venture ahead into the foggy territory of climate mitigation in order to avoid that danger. But because it is foggy, they are tentative and naturally reluctant to go first. The developing countries (reasonably) think that the richest and safest countries, the ones responsible for a lion’s share of the emissions, should taken on a lion’s share of the economic risks of mitigation, at least at first. And again, that’s what the U.S. would be taking on: not pain but risk.

Along with the risk that we’ll hurt our economy through the loss of carbon-intensive industry is the possibility that we will position ourselves for long-term success in the burgeoning clean-energy industry. All the models in the world won’t give us certainty about how those risks and opportunities balance out. (Though it’s worth noting that virtually every advance in clean air and water in our history has come at lower cost and greater benefit than expected.) Only action will reveal the truth.

Anyway, these arguments are familiar and too complex to be settled here. For my part, my response to the sophisticated objection is somewhat less sophisticated.

Arguments about the cost of climate action have traditionally emerged out of models contemplating a 2 degree rise in global average temperature by the end of the century. But that is no longer what we are facing. We are now on a trajectory toward 4 or even 6 degrees. Reviewing the science, the World Bank was recently moved to warn that “there is no certainty that adaptation to a 4°C world is possible.” Climate scientist Kevin Anderson, of the the U.K.’s leading climate research institution, the Tyndall Center, has said the following:

[A] 4 degrees C future is incompatible with an organized global community, is likely to be beyond ‘adaptation’, is devastating to the majority of ecosystems, and has a high probability of not being stable.

Not only does 4 degrees potentially threaten the ability of human beings to maintain advanced industrial societies, it is almost certainly a waystation along a path to even higher temperatures. By the time we get to 4 degrees, the earth’s biophysical systems are likely to be changing with a momentum that is unstoppable. We won’t just be condemning the people of 2100 to misery, but every generation thereafter as well, for centuries to come.

This new reality recently moved famed climate economist Nicholas Stern, author of the Stern Report, to say recently, “I underestimated the risks.” And you’ll recall that the Stern Report was denounced as “alarmist” when it came out. Discussion of climate by Very Serious People like Sunstein (and Salam) simply hasn’t grappled with climate situation as we now understand it.

So that’s the response to the sophisticated objection: The U.S. must act because all people have a moral obligation to act. We have no guarantee that if we act, others will act; we have no guarantee that if everyone acts, it will be enough. But inaction is not a choice. If the danger were an invading army from another planet or a raging global pandemic, we wouldn’t be having these arguments. The need for everyone to act would be obvious. Quibbles over who acts first, or who benefits most from the planet not being invaded, or how to avoid spending “too much” to avoid being annihilated would rightly be seen as verging on sociopathic. Everyone would be eager to act, despite having no certainty of success, because the alternative is simply unacceptable.

That’s the root of it: The results of inaction are morally unacceptable. They are also economically unacceptable, worse than virtually anything we might inflict on ourselves through too-vigorous pursuit of clean energy, regenerative agriculture, reforestation, resource-efficient land use, and resilient infrastructure. But ultimately it is a moral argument. We know we are on track for unthinkable human suffering and we know how to avoid it. Even if we can’t make a dime by saving millions of future children in Africa and Asia, we ought to save them. Even if we’re not certain of our success, we have to try. It’s a matter of human decency.

There was a time, not that long ago, when America took pride in leading the world against such dangers. Where is that pride now?