The Hiatus – Cohn’s Overview and Held’s Observation

Journalist Nate Cohn takes on the hiatus at New Republic, and on the whole does a fine job of it, identifying key dramatis personae and getting mostly good quotes from them. There are a couple of unfortunate lapses in clarity (the “cancer” analogy is never explained in any sensible way – I sure didn’t understand it anyway) but such lapses aside a reader could come away from the article with a good grasp of what is really going on.

But the “consensus” never extended to the intricacies of the climate system, just the core belief that additional greenhouse gas emissions would warm the planet. The greenhouse effect is truly undeniable—just consider Venus, where 96.5 percent of the atmosphere is composed of carbon dioxide, and the average surface temperature is more than 860 degrees Fahrenheit. Conversely, without greenhouse gases, Earth’s average surface temperature would be 0 degrees Fahrenheit.

And once you concede the existence of the greenhouse effect, it’s tough to dispute the role of greenhouse gas emissions in warming the planet: Over the last ten years, increased carbon emissions added trapped about as much heat in the climate system as small volcanic eruptions, the solar cycle, and stratospheric water vapor combined to deduct. But since the start of the industrial age, carbon dioxide has added nearly seven times as much positive forcing, and that number will keep growing with additional carbon emissions.3 So here’s what’s clear: Over the longer term, temperatures will increase. As Held puts it, “warming over 100 years isn’t that sensitive to fluctuations.”

“I don’t see how you can argue against it,” Solomon observed after declaring that “carbon dioxide will be king over the long run.” The amount of warming over the last century has not been small, and there “has to be a source, if you believe in basic thermodynamics.” Skeptics point to internal variations—the natural shifts that scientists have struggled to explain over the last decade. But oceanic heat content has also been increasing, ruling out the possibility that atmospheric warming is due to internal variability. To Held, that’s “pretty much a smoking gun.”

I think it might be worthwhile to expand a bit on Held’s point, which is one I had not heard made before.

Natural variability on time scales of years to decades that affects the global scale has to be driven by heat exchanges between atmosphere and ocean: there is no place else for the heat to go. So if CO2 forcing is unaccountably much weaker than we suppose, and we are seeing unforced natural variability, the 20th century atmospheric warming would have to be balanced by oceanic cooling. There are no other candidates for an unforced variation on the appropriate time scale.

Of course, it’s “a” smoking gun. It stretches the smoking gun analogy, because there are several streams of evidence pointing to the same culprit. We really shouldn’t be arguing this anymore, never mind with the vehemence that always seems to go along with it. Clearly, the problem is not in the science itself, but in the connection between science and politics.


  1. Your point, nicely spiced with Russell Seitz's cite, is well taken. The argument is a total success from the point of view of delay creation. It can be empty of facts, but serves the purpose of preventing intelligent planning and action.

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