Megan McArdle, writing in Bloomberg View, argues that the climate debate should be a lot less heated, and that so-called “lukewarmists” deserve a fair hearing. She writes:

Skeptics are accused of being ideologues, or in the pay of the fossil fuel industry, or simply selfish monsters who care nothing for future generations. The other side — who expect big temperature jumps and catastrophic consequences — are accused of being ideologues, or interested in making an alarmist case in order to further their own careers as climate change activists, or authoritarian monsters who are less interested in saving the planet than in forcing their own left-wing economic order on the rest of the world.

McArdle’s right. It’s time for de-escalation in this war of dueling caricatures. The problem is so bad that even deliberate attempts to foster reasonable discussion can end in ad hominem attack or sanctimonious dismissal. This is precisely the sad fate McArdle’s piece suffered. Her follow-up offers a vivid demonstration of the way a call for even-handed discourse on climate change can devolve into insults.

I welcome a continuously renewed conversation. We try our best to the keep it civil and substantive here at the Niskanen Center. And in this spirit of reasoned and informed discussion, I’d like to offer some comments on what McArdle has to say about the substance, as well as the rhetoric, of the climate debate.

McArdle appears reluctant to embrace the predictions of climate models under the assumption that they are similar to mid-century macroeconomic models, for which “only the unflappable true believers place great weight on their predictive ability” these days. In particular, she worries that climate models “involve a lot of theory and guesswork” about amplifying feedbacks that enhance the uncontested warming effect of CO2, which places her in the company of lukewarmists. She writes:

This lesson from economics is essentially what the “lukewarmists” bring to discussions about climate change. They concede that all else equal, more carbon dioxide will cause the climate to warm. But, they say that warming is likely to be mild unless you use a model which assumes large positive feedback effects.

The desire to be cautious with models of complex systems is completely reasonable. But there are important differences between macroeconomic and climate modeling that limits the usefulness of the analogy. In the end, it is very possible that today’s climate models provide a well-calibrated range of predictions that will more or less come to pass.

No climate modeler begins by assuming large amplifying feedbacks. They model phenomena that need to be in a climate model. Some of those phenomena, such as the quantity of water vapor in the atmosphere and the formation of clouds, may change as CO2 warms the climate. The model needs to take that into account. The amplifying feedbacks come from the combined effects of these various interacting physical mechanisms.

Now, it’s true that the choices modelers make matter. Clouds especially are a challenge to incorporate into climate models, and different assumptions–all of which reasonable–can exert an uncomfortably powerful influence over the strength of amplifying feedbacks. So it’s not like scientists can say “But physics!” and dismiss McArdle’s concerns. We need to keep uncertainty in mind.  

I don’t understand, however, why it is more reasonable to assume, a priori, small amplifying feedbacks rather than large ones. You need to have a reason based in theory and evidence to prefer the hypothesis that feedbacks are small. It’s arbitrary to treat the lower estimate as more likely than the higher estimates without an accounting of why. It is especially arbitrary to do this when you’ve just emphasized the unpredictable complexity of the climate. It can’t be both so complex as to defy confident prediction and predictably modest in terms of its response to CO2.

I’ve argued before that the lukewarmist case for small climate feedbacks relies on a selective reading of the evidence. This tends to involve not only dismissing climate models, but also much of what we know from studies of the pre-human climate. I’ve also discussed how studies frequently cited by lukewarmists are frequently subject to serious criticism and reevaluation. In any case, the existence of the debate illustrates why climate forecasts from groups like the IPCC incorporate a fairly large degree of uncertainty about future warming.

As important as assumptions about feedbacks may be for climate models, it’s important not to allow the complexity of the system to effect our interpretation of basic physics. The bulk of climate modeling is more straightforward than some people familiar with complex systems in the social sciences might imagine.

There are many factors that warm the climate and many that cool it. The principal work of climate modeling is to take a complete census of all of these factors, estimate the sizes and trajectories of their various effects, and then add them up to estimate future global temperatures. When you leave the light on in your kitchen, for instance, it warms up the room a little, and when you open the freezer it cools it down a little. Much of climate modeling is more like modeling the offsetting effects of lightbulbs and open freezer doors than it is like modeling systems in which everything affects everything else in an unpredictable way.    

For large scale quantities like global temperature, climate models seem to do this well. When given the full suite of warming and cooling effects, models reproduce climate outcomes rather. This slideshow shows how well models predict past temperature trends, and the extent to which human activity was the primary cause of warming over the last century.  When all of the warming and cooling agents we know of are properly included, the models reproduce the past fairly well and global temperature responds quite proportionally to increases in warming effects.

In terms of prediction, there is little reason to think that response of the climate to CO2 will change dramatically in the future. Climate models are based on the laws of physics, and those laws are immutable. To be sure, there is a lot of complexity in the way the change in average global temperature will play out regionally, or in the occurrence of phenomena like hurricanes or forest fires. But for large scale responses to increasing CO2, there isn’t much reason to think climate models are missing something of major importance.

McArdle doesn’t dive deeply into a discussion of climate policy. That’s understandable, because her point is that “the science” is consistently used as a cudgel to beat people into the idea that policy action of this or that flavor is urgently necessary. I wish this would stop as well. “Alarmism” encourages the idea that the case for relatively aggressive climate policy rests on the claim that climate change is more likely than not to produce catastrophic outcomes. But it doesn’t. Alarmism isn’t necessary to justify taking action. Even lukewarmism will do.  

In her piece, McArdle cites an extensive series of blog posts by Warren Meyer as an example of the sort of probing, level-headed argument she’s calling for. Meyer walks through the reasoning that leads him to be lukewarm about climate risks (I don’t agree substantively, but I agree he walked through his reasoning clearly). According to Meyer, the evidence for an imminent man-made climate catastrophe is limited.

Nevertheless, in his final blog entry Meyer voices support for a carbon tax (and a corresponding reduction in payroll taxes), as a low-cost insurance policy against climate risk. This is very close to my own position. Meyer says that he does not think a focused federal climate policy such as a carbon pricing is strictly necessary, but he does see it as a vast improvement over the stew of command-and-control regulations, green energy subsidies, and Solyndras that we’re getting now. Bravo.

Meyer understands that climate policy design is not exclusively a question of science, but one of risk tolerance, politics, and economics, and that even a lukewarm future may have hazards worth trying to minimize. For her part, McArdle emphasizes that she’s more inclined than Meyer to support action to guard against even a very low-probability risk of climate catastrophe. She’s quite right to suggest this correction to Meyer’s analysis.

Climate activists are prone to see lukewarmism as a slightly more sophisticated but still fundamentally obstructionist form of denialism, and not without reason. Criticism of climate science, and criticisms of scientists, has been a key rhetorical strategy of those opposed to climate action for decades. Some activists will wonder why they should respectfully engage lukewarmism just because abject denialism has become untenable.

Here’s why: because Meyer and McArdle’s thoughtful openness to some climate action, even if it’s not exactly enthusiastic, shows that lukewarmism isn’t necessarily a rhetorical bulwark to meaningful climate policy. On the contrary, lukewarmism is often the sincere opinion of a good number of intelligent people of good will. And when extremely intelligent people of good will go out of their way to ask for a more civil conversation about climate change, those of us who think it’s important to take action on climate change sooner rather than later need to listen carefully and respond with respect.


[Image Source: Star Tribune/AP]