Complication and Climate Communication

In response to CNN’s termination of its science/tech/environment unit and continued questioning of anthropogenic climate change, personal friend Peter Offenhartz wrote me to comment that while CNN’s move is “impossible to understand,” the continuing controversy over climate change is less perplexing.

In his email, Offenhartz suggests that part of the problem lies with the climatology community, which has not excelled at simplifying their models’ main results so that ordinary people can understand them. “The evidence is not so hard to understand as most people seem to think,” he writes. Offenhartz, a physical chemist, makes his case by offering the informal lecture on climate change that he’s been sharing socially in recent weeks. His explanation highlights the idea that rising CO2 matters most where water vapor concentrations are low: (emphasis Offenhartz)

My trouble with the climate guys is they don’t want to say this. They don’t even want to say water vapor is a greenhouse gas, even though they know that ON AVERAGE water vapor accounts for about 2/3 of the greenhouse warming from -15C to +15C.

Water vapor’s role is indispensable in Offenhartz’ view because it provides an explanation for why global warming is hitting the poles and glaciers the hardest – a differential impact that cannot be explained by the sunspot activity that climate skeptics credit as the cause for global warming.

To paraphrase Offenhartz: Colder air generally contains less water vapor, whereas the concentration of carbon dioxide is quite uniform around the globe. However, the two gases’ effects on global warming are not independent because water vapor and carbon dioxide absorb and trap some of the same wavelengths of heat radiation from the Earth. As a result, concludes Offenhartz, “the effects of rising carbon dioxide concentrations are greatest where water vapor concentrations are low”:

Rising CO2 causes the melting of arctic ice. That, I think, is indisputable.

Exasperated climatologists trying to sharpen communication of climate science, such as the folks at RealClimate, might well respond by pointing out that the greater absorption by CO2 at high altitudes is neither the whole story, nor is it free of controversy.

It’s not the whole story because (a) decreased reflectivity at the poles from melting sea ice are expected to play a larger role in differential warming of the poles and (b) there has been some debate as to whether the temperature ‘fingerprint’ climate models predict for the poles has been observed definitively. See, for example, this recent discussion of Arctic amplification by Mark Serreze and Andrew Barrett at the University of Colorado’s National Snow and Ice Data Center.

Then there’s the fact that climatologists are often criticized by climate skeptics for allegedly ignoring water vapor’s significance. Offenhartz’ communications strategy might leave climatologists open to a charge of oversimplification, but they’d never again stand accused of overlooking the role of water vapor!

Peter O’Donnell Offenhartz earned his Ph.D. from the University of Pennsylvania in 1963. He is the author of the graduate text Atomic and Molecular Orbital Theory, which still fetches $30+ on Amazon almost four decades post-publication, as well as the commercial molecular spectroscopy software package Molspec which predicts the absorption spectrum of any gas mixture (including water vapor and carbon dioxide) under a wide variety of conditions.

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