By Fred Paillet, OS Education Chair
Climate change is a major environmental concern, and we can see its effect in a worldwide retreat of glaciers as in my illustration below. But those glacier retreats occur in remote places or affect sea level in coastal locations while Ozark residents are primarily concerned with what is happening in their midcontinent location. As a professional geophysicist deeply versed in climate science, I remain dismayed by the way the subject of Climate Change is most often presented. First, because we mostly hear about a degree or two of temperature change as if that in itself is a physical calamity. Then, the difficulty in believing that human activities discharging exhaust gases in scattered locations could possibly pollute the vast ocean of air above us.
The big problems inherent in climate change are related to extremes such as droughts and flood and not simple daily averages. A topic you can easily google is found under the heading of “polar amplification” – a phenomenon that has important consequences for weather extremes. This is the long substantiated (at least for climate experts) fact that an average global temperature change is not uniformly applied to the globe, being amplified three-fold (or more) at the poles. That is, an average change of a degree (no matter what kind) translates into a third of a degree at the equator and three degrees at the poles. Many of those struggling just to survive may quietly think that saving a few arctic creatures is nice idea but a luxury we can’t afford if it impacts the cost of energy.
Instead of fixating on average temperatures, let’s think about how global warming might impact weather patterns. Since extremes are the real problem, consider how transfer of solar heat (the energy driving our weather systems) occurs in the manufacture of our daily weather. Could even modest climate change have an effect in that regard? Rather than equatorial heat simply flowing down a thermal gradient, our weather is created by bubbles of hot air wandering north and being replaced by cooler air from the polar regions. Weather prediction is based on monitoring “bulges” as they develop into the advancing bubbles behind cold and warm fronts. These are known as Rossby waves in honor of the Scandinavian meteorologist who first described them. These waves develop on the temperature contrast between air masses we see as the jet stream. Atmospheric dynamics require that there be a strong flow along the boundary separating air masses of differing temperature (thermal wind). Global circulation models clearly show that a change in the temperature differences driving Rossby waves changes the properties of those waves. By analogy with the tension on a guitar string, a reduced tension causes a lower (longer wavelength) sound. Longer Rossby waves have bigger excursions and travel slower. That’s the mechanism by which a small change in global temperature distribution (and the larger change to global temperature gradient that goes with it) can create a big change in storm dynamics.
Water vapor provides the energy within storm systems, and the amount of vapor air can hold increases sharply with temperature – perhaps a hundred-fold over the temperature range from arctic to tropical. It’s the combined effect of more water vapor content and slow-moving storm systems that will create the most flood hazards. This belies one common myth that global warming will only increase rainfall as a blessing to the world. In fact, it is more likely rain will simply fall where it is already abundant and less in places where it is already scarce. Some folks take comfort that the slightly greater summer temperatures of the altithermal period about 8000 years ago (part of the excruciatingly slow glacial-interglacial cycle) created a green Sahara and brought summer monsoon rains into the Great Basin Desert. Increasing carbon dioxide in the air will change the retention of solar heat in air equally over land and sea, a far different effect with different expected results. I would not invest in Saharan farmland as a hedge on global warming.
Next, let’s consider how human activity could possibly affect our vast ocean of air. Actually, it is more of a thin blanket than an ocean. The troposphere is maybe 7 miles thick. The earth is 8000 miles in diameter. If you scale down the earth to the size of basketball (8000 miles to a foot), the air blanket is hardly more than the thickness of a couple sheets of paper. That gets your attention. Even harder to refute is the steady observation of CO2 in the atmosphere famously undertaken by Keeling, documenting an increase from a base level below 290 to more than 400 ppm. That’s more than a 35% increase that cannot be denied except by conspiracy theory nut cases who claim the measurements are faked. But have we been adding enough CO2 to account for what could just possibly be a naturally occurring effect? A rough estimate of the amount of CO2 put into the air by human action each year comes to about 1% of all the CO2 originally there – about 75% from fossil fuel burning, and the rest from forest fires, livestock concentration, and oxidizing of plowed soil. It is fortunate that the yearly addition does not all remain in the air because atmospheric CO2 would have doubled by now. In fact, a little less than half must be retained to account for the observed Keeling Curve increases. A good part of our emitted CO2 is absorbed by the oceans. Even that isn’t good news since that increases ocean acidity and interferes with the ability of coral and other sea life from microscopic coccoliths to giant clams to synthesize the limestone they need to survive.
The carbon budget numbers demonstrate with no doubt at all that human activity is more than enough to account for the observed upward increase of CO2 in the atmosphere. The seemingly alarmist claims by climate scientists that weather extremes will be the result of climate change are not fanciful scenarios intended to enhance their funding. Sound atmospheric science has shown that global temperature change translates into three-fold enhanced changes in the thermal gradient that drives our weather systems. Some enhanced water vapor capacity will contribute, but larger and slower moving frontal excursions have been the base of disastrous flood and drought extremes of the past. We can expect more of them in the future (like the infamous polar vortex) as global temperature increases by what otherwise would appear to be a modest amount.