Bill Nye the Climate Guy

kw: book reviews, nonfiction, scientific method, climate change, polemics

Bill Nye is one of my all-time favorite people. The fact that I was dismayed by some aspects of his recent book doesn't diminish my admiration for him. He is a top-notch science educator and a writer I enjoy reading.

Bill Nye's new book, Everything All At Once: How to Unleash Your Inner Nerd, Tap into Radical Curiosity, and Solve Any Problem, is ostensibly about that middle phrase: "Release your inner nerd." It is primarily an evangelical work, aimed at anyone on the fence between those who "believe" in climate change and the climate-change "deniers". Along the way, though, he offers great examples and advice for many folks who may be a bit tech-averse, to see how humans are by nature technical beings, and that solving problems is what we do best—or we can, if we go about it right.

I hope a great many people will indeed read this book. It is very well written. The author manages to press his pro-climate change case pretty hard without becoming entirely disagreeable. I will address my concerns in a moment.

Let me first state my background in the matter; it is a subject I have followed for nearly sixty years.

When I was a child I heard about the "Greenhouse Effect". It was already old news, because the term was used by Svante Arrhenius in 1896 to describe his calculations that a doubling of CO₂ concentration in the atmosphere would raise average global temperature by about 5°C (that is 9°F to us Americans). At the age of twelve I was able to learn enough math to reproduce Arrhenius's result.

In actuality, "greenhouse effect" is not an entirely accurate metaphor. In a greenhouse, the glass physically traps air warmed by the sun, while also providing spectral emissivity to enhance the effect. A "greenhouse gas" cannot physically trap warm air, but causes extra heating solely via spectral emissivity.

The terms "Global Warming" and "Climate Change" began to be used by some in about 1975, and their use ramped up greatly after 1985. "Greenhouse Effect" also took off about that time, when the atmospheric effects they all refer to became a political football. Then a funny thing happened. Looking at the Google Ngram Viewer, I find that since 1992 "Greenhouse Effect" rapidly fell out of favor, "Climate Change" became the term of choice, with "Global Warming" running a rather distant second.

The problem with all this is that "Greenhouse Effect" denotes a possible cause, while the other two terms refer to effects. So now let us back up and examine the term I threw in earlier, "Spectral Emissivity". For solid materials, this refers to a departure from the spectral behavior of a blackbody or graybody. If we could produce a paint that was perfectly gray—at any level of grayness—throughout the electromagnetic spectrum, we could paint it on a surface and it would cause an amount of heating, when the sun shined upon it, directly correlated to the total emissivity. To be specific, a perfect blackbody surface will heat up to a temperature that depends only on the energy being radiated to it. It has an emissivity of 1. A perfect reflector will not be heated at all. It has an emissivity of 0. A perfect graybody surface with emissivity of 0.5 will heat up to an intermediate temperature according to a proportional constant times the Boltzmann factor t⁴.

Now, consider a "step-spectral" surface. Suppose it has an emissivity of 1 for visible light, and an emissivity of 0 for infrared light. Let's put the cutoff at 700 nm. A surface with this characteristic, in a vacuum so air will not carry off any heat, and with only visible light shined upon it, would heat up until it was hot enough to radiate away that same amount of radiant energy. In visible light it would appear black. It absorbs light, but if it is cool, emits nearly none. Thus it must heat up. You might know from experience that the heating element in an oven gets to about 600°C before it begins to glow reddish, and at 800°C it is getting orange-red. The great majority of its radiation, however, is at infrared wavelengths longer, much longer, than the 700 nm radiation we call "deep red". If it is prevented by the step-spectral emissivity from radiating at those longer wavelengths, it must, perforce, heat up until it is radiating a lot of visible light, to balance the incoming light. Thus a step-spectral surface tends to get very hot indeed, hotter than an oven element.

Now we can consider gases. Oxygen and nitrogen hardly absorb any light at any wavelength of interest to us as we consider the heat balance of our atmosphere. There is a common gas, however, that does absorb a lot of light, at a range of wavelengths that make it a strong greenhouse gas. That is water vapor. Surprised? We will look at some spectra in a moment. First, qualitatively, we find that water vapor absorbs a lot of ultraviolet light, but absorbs even more strongly in several ranges throughout the infrared, with narrow absorption bands at about 1.2 and 1.9 microns, a wider band from 2.5-3 microns, and a wide, almost total absorption feature from 5 to 7.5 microns. The result of this is that if Earth had no atmosphere it would be 32°C (about 60°F) cooler than it is. A perpetual ice age without the ice. So water vapor is by far the strongest greenhouse gas, and is responsible for life being able to exist on earth.

"Climate Change" is all about carbon dioxide (CO₂). What does this gas do? It also has spectral emissivity, with an absorption band at about 2.7 microns, a stronger one near 4.2 microns, and a third between 12-16 microns. This last one is of primary interest. It is perfectly placed to absorb about 10% of the thermal radiation from warm dirt, meaning that the dirt has to get a little warmer to radiate that extra energy at other wavelengths. And that is what is behind Arrhenius's greenhouse effect calculation.

Greenhouse gases operate a little differently from painted surfaces. Dirt and other stuff on Earth's surface has spectral emissivity, of course, but not nearly with the perfection of the step-spectral material discussed earlier. So it reflects a lot of light, absorbs some, and gets warm enough to radiate some infrared. In a vacuum, dirt with sunlight shining on it would have some specific temperature. Now put a layer of greenhouse gas above it, an atmosphere containing water vapor. The incoming sunlight is not affected much. But the outgoing infrared from the warm dirt is partly absorbed by the water vapor, which heats up and radiates also, with half going up and half going down. This causes the dirt to get warmer, until it is able to radiate enough to balance its thermal outflow with the radiative inflow from sunlight and also the re-radiated infrared from the warm air above it. How does CO₂ modify this picture? It absorbs a little more infrared radiation, in portions of the spectrum in which water is rather transparent. So CO₂ strengthens the greenhouse effect. Now, here are the spectra:

I don't know the original source of this graph. It is found all over the place. It also shows a tiny contribution from oxygen and ozone, but we won't consider those here (in the "ozone layer" the temperature goes up significantly, however).

The blue line is for water vapor. The curve marked 255K shows the thermal radiation from a piece of ice at -18°C or 0°F. "Room temperature" is close to 300K or 27°C (81°F). Its radiation curve would be a little to the left of the one shown.

The point is, water vapor reflects back a lot of the radiation from the earth and even from glaciers. Yes, glaciers radiate infrared also. The blue line is for water vapor with a content near 0.3% of the atmosphere, or near saturation (100% relative humidity) at ice temperature. The CO₂ curve is for a few hundred ppm; the sources I read didn't state exactly. The result of increasing the amount of CO₂ would be to widen the bands, as their "wings" absorbed more and more. This shows what happens when these two gases lead to greenhouse warming.

Now it is a separate issue, whether this is actually causing climate change. "Deniers" say not so, proponents of the idea that CO₂ is a "pollutant" say it is. I won't get into that. We have measured that, from the time I was a little child and there was less than 300 ppm CO₂ in the atmosphere, and today, when the amount is 400 ppm, global atmospheric average temperature has risen just under 1°C.

Is that a lot, one degree C? Let's look at one factor. Water expands when heated. Heating water by 1°C yields an expansion of 0.000214, or 0.0214%. The ocean averages four km in depth. If the entire ocean were warmed by 1°C, it would be 0.000214x4,000m = 0.856m deeper (33.7 inches). That is enough to force the evacuation of some low-lying areas and certain island nations such as Tuvalu. "Climate evacuation" has already started. But has the whole ocean heated by that much? Not yet. Give it time. The early evacuations were the result of less than one-third of this figure.

I'll stop there. These are not easy points to make with a public that largely doesn't care. Thus, Bill Nye's passion. He wants to make everyone care. But as I read I took careful note: will he mention water vapor? He does not, except for a throwaway phrase in a late chapter. We can't ignore water, for another reason. Trapping a little more heat means adding energy to the system. That means more water could evaporate. Whether it will or not is a huge area of controversy in the climate modeling arena. Water is complex. It might be the most complex substance there is. It is possible that the added energy will yield a net drying rather than adding more water. We might see more rain, or less rain, overall, and nobody yet has a good handle on which areas might experience greater or reduced rainfall. Oh, I've seen a few predictions, but none is well supported by robust evidence.

I agree with Bill Nye, though, that we need to be reducing our dependence on "convenient" energy from burning stuff (mainly fossil fuels), and toward solar, wind and other "alternatives". A generation ago the oil companies began calling themselves energy companies. But they are really still oil and coal and gas companies, with only tiny amounts being spent on non-carbon energy production. They could become the heroes of the 22^nd Century. But I fear they will more likely be the goats. I just don't know who else has money enough to do the research to make solar and wind as ubiquitous as they need to become. And there, I think the Science Guy might agree. Read the book. Agree with Bill Nye or not, you're in for a fun ride.