Is the Climate Less Sensitive than We Thought?

At DotEarth, Andrew Revkin summarizes recent research that is leading to some to conclude that the climate is less sensitive to greenhouse forcing than previously thought.  He writes:

on one critically important metric — how hot the planet will get from a doubling of the pre-industrial concentration of greenhouse gases, a k a “climate sensitivity” — some climate researchers with substantial publication records are shifting toward the lower end of the warming spectrum.

There’s still plenty of global warming and centuries of coastal retreats in the pipeline, so this is hardly a “benign” situation, as some have cast it.

But while plenty of other climate scientists hold firm to the idea that the full range of possible outcomes, including a disruptively dangerous warming of more than 4.5 degrees C. (8 degrees F.), remain in play, it’s getting harder to see why the high-end projections are given much weight. . . .

The reason it’s worth working to clarify what’s going on is that a lower climate sensitivity could substantially expand the timescale on which decarbonization of humanity’s energy menu would need to take place to blunt climate change. This could raise the odds of a Thornton Wilder ending to our “large-scale geophysical experiment.”

This does not mean we should stop worrying about global warming.  As I’ve noted before, even if a doubling of carbon-dioxide-equivalent will produce warming at the low end of conventional projections, it is still a serious concern (even from a libertarian perspective).  But it’s also important to get the science right, and not base policy on exaggerated fears or implausible scenarios.  And more importantly, given the enormous difficulty of stabilizing atmospheric concentrations of greenhouse gases in the near-to-medium term, it would be good news if the rate and magnitude of future warming will be less than some fear.  After all, it’s not as if we’re going to prevent climate change by adopting a “more  European” work schedule.

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