A friend pointed me to an interesting video about “Global Dimming”. After watching for a while and then finishing by reading the transcript, I did some more reading and thinking. (There is a good article titled Global Dimming and climate models available on the excellent climate resource named Real Climate)
I have just spent a fascinating couple of hours learning more about climate models and global dimming, so I have enough knowledge to be dangerous.
Looking at the issue with the eyes of a nuke, however, I thought of a couple of things that may be worth discussing. Forgive me if I make a few over simplifications – I am, after all, just an English major who went through nuclear operator training and ended up in charge of a submarine engineering department.
The climate is a pretty complex beast with lots of factors that affect its current condition. Back in my nuclear training, I spent a lot of time using the “6 factor formula” which is a simplification of the hundreds of factors that affect the rate at which fission occurs in a reactor. It is a differential equation in which all of the factors played a varying role in the overall rate of fission (also referred to as reactor power.) Often, the real key was not the absolute value of the factors, but the rate at which they were changing. (Hence the use of differential equations.)
When people point to the very small percentage contributions of man made emissions, that does not convince me that they are unimportant. In a critical reactor (the stable condition of a power producing reactor), the power and temperature levels are constant, but very small changes (like the quantity of Xe-135) can have a large impact on the temperature at which the reactor is critical. A mere bump in a group of control rods can make up for that change.
When nukes get together to chat about the various effects of certain events on reactor power (yes, we really do that for entertainment), we cannot always quantify the values of the various factors, so we use something called “arrow analysis” where we indicate whether we think a certain factor is going up or going down. When we have more detailed information, we make the arrows larger or smaller to indicate the actual size of the effect. We are comfortable with the concept that the overall changes cannot always be determined by focusing on only one or two of the factors and that seemingly small factors often matter more than we would have initially thought.
Man made changes in atmospheric components are not limited to burning fuels, they also include our effects on the population of cows, the density of the plant life, and our own human population of CO2 producers. It still seems logical to me that atmospheric and climate stability is aided by keeping changes to a minimum.
I also spent a lot of time thinking about the effects on the water cycle of reducing the actual energy of the sun that impacts the 70% of the earth’s surface that is water. The temperature of water is not the only thing that governs its evaporation rate – the latent heat of vaporization means that it can take as much as 540 times as much energy to turn a certain quantity of liquid water into vapor as it does to raise the temperature of water one degree.
Air pollution logically reduces the rate of evaporation by reducing the solar energy entering the water. The thicker and more widespread the pollution layer the larger the effect. That implies that the total fresh water production in the world will be reduced by increasing pollution, even if that seems to help mitigate the effects of a greenhouse gas caused temperature increase. In a world with an increasing population, we need all the fresh water we can get – though floods are not always welcome, even they can have beneficial long term effects.
Of course, the effect of pollution on evaporation is reduced by the fact that pollution is somewhat locally distributed and people do not populate and pollute the ocean areas as much as they do the land areas. As someone who has spent a few years at sea, however, I can tell you that human generated pollution is more widespread over the ocean that one might imagine.
Of course, all of these thoughts just made me continue to marvel at the possibilities of reducing our overall effect on the climate by shifting more and more of our energy production to a source clean enough to run inside a submarine. As we used to teach our reactor operators – if you are not SURE what change to make, do not make any change at all.