Mike Johnson: "I don't think..."

The new Republican speaker of the House, Mike Johnson, said this at a town hall in 2017: "The climate is changing, but the question is, is it being caused by natural cycles over the span of the Earth’s history? Or is it changing because we drive SUVs? I don’t believe in the latter. I don’t think that’s the primary driver."

Johnson doesn't think burning fossil fuels (for which driving SUVs is his dismissive proxy) is the "primary driver" of present-day climate change. I would suggest that he doesn't think at all.

Which sums up the problem in a nutshell. Does he have an opinion? Yes. Does he think? No.

There are several important "drivers" of "natural" climactic variation (to which Johnson offers a handwave) over geologic time. One is periodic changes to the axis-tilt of the earth, plus changes in the shape of its orbit. These give us ice ages, when prevailing geological processes permit. The science of ice age formation is very well understood.

Another long term driver of "natural" climactic variation is the interplay between geological processes that emit carbon into the atmosphere, and those that remove it, typically playing out over millions of years. I wrote about this recently.

Whatever climate process we consider, carbon dioxide is always in the thick of it, either as a primary driver of change, or as (in the case of ice ages) part of a feedback mechanism. Carbon dioxide is itself the earth's most important greenhouse gas, and is the fundamental determinant of the planet's temperature. Earth would be far colder without an atmosphere containing CO2.

The correspondence between changes in atmospheric CO2 concentration and changes in the temperature of the earth is well understood. The mechanism of that relationship is rather elementary physics, involving how greenhouse gas concentrations make the atmosphere more or less opaque to outgoing infrared radiation. I touched on that here.

The actual atmospheric CO2 concentration has been precisely measured since 1957. The upward march of CO2 concentration over that period is shown graphically by the Keeling Curve. The sawtooth shape of the curve even demonstrates atmospheric CO2 fluctuations between northern hemisphere summers and winters. (The northern hemisphere has far greater land area than the southern hemisphere; CO2 is absorbed by plants during its growing season, which biannually modulates global CO2 concentrations.)

We know that the atmospheric CO2 concentration was around 280 parts per million (ppm) at the beginning of the Industrial Revolution. The measured concentration in 1957 was 315 ppm. The measured CO2 concentration today is 416 ppm, an increase of almost 50 percent since the beginning of the Industrial Revolution: a breathtaking increase in so short a time. We know that increase is due to the burning of fossil fuels, as a consequence of industrialization. Because fossil fuels are a global commodity, we can calculate how much CO2 we emit by burning them, and we can confirm how that correlates with the atmospheric concentrations we measure. We also know there are no natural sources of CO2 emissions happening that could explain the rapid increase now occurring. And we know that the rate of increase right now is far more rapid—stupendously more rapid—than any that has occurred under natural conditions in the geologic past.

Everything I've said here is well understood. Much of it is rather elementary at, say, the level of a first-year physics undergrad. And while we might not expect everybody to have mastered all these details, we can expect everybody—especially policy makers and legislators (and you!)—to at least grasp that scientists understand the science, and in broad strokes that understanding is not controversial among those with the relevant subject matter expertise. In fact, there's enormous scientific consensus that anthropogenic (human caused) climate change is real.

We could also add that over the past several decades the science has been highly predictive of conditions as they have unfolded—so much so that the likes of Mike Johnson, the new speaker, acknowledge that the climate really is changing. It's just that he doesn't think it's for the reason scientists say.

Which is tantamount to him saying I don't think at all. By what authority does he form his beliefs on a question that is fundamentally scientific?

If Johnson is going to offer a contrary opinion, oughtn't he be obliged to at least say why he thinks the climate is changing? Don't hold your breath. All he offers is a handwave, one you can expect to hear a lot more of as the changes now manifesting, this year rather dramatically, become increasingly undeniable. As we saw above, Johnson's handwave is this: Presently-observed climate change is "caused by natural cycles over the span of the Earth’s history." None of which Mike Johnson understands. Nor will he make any effort to understand.

It's important to realize that waving at natural variation itself explains nothing. You still need to elucidate the physical mechanisms underlying natural variation, and contrast those mechanisms with what's happening now.

Science does understand those natural variations, some of which I've mentioned here, and explained in the links above. Science very much understands how atmospheric CO2 concentrations are involved in Johnson's "natural cycles." And it understands how the very rapid increase in CO2 concentrations occurring right now are a result, pure and simple, of human emissions. Science explains the why and the how. And thus it understands that humans are rapidly warming the planet. This time there's nothing "natural" about it.

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