Alternative Climate-Change Theories
So far, we have primarily considered only the sun’s role in natural climatic change. This focus does not imply that the sun is the only cause of climatic changes, nor even the most important one. In the last chapter, we stated that solar and climatic changes have paralleled each other for the last four centuries and, therefore, on time scales of decades to centuries, solar variations might be a dominant driving force for natural variability. Many climatologists adamently disagree with this conclusion and suggest that other factors, both in the past and for the future, are far more important. In the future, mankind’s influences may increase and likely will dominate coming climate changes. One hypothesis suggests that the climate system varies randomly, first warming for a few decades and then cooling. Scientists who support this hypothesis believe that external influences need not necessarily cause internal changes. They view the Earth as a thermostat with a very wide interval (or band) of possible temperatures. In other words, the Earth’s mean temperature is not constrained to one precise equilibrium temperature. Several natural experiments contradict this belief. For example, following a volcanic eruption the Earth cools for a few months to a few years; then the temperature returns to its preemption values. This rapid return implies a narrow stable temperature band, with the climate system striving to return quickly to its equilibrium. As the time constant for the climate system is relatively short, it responds quickly to variable forcings. Similar arguments can be made using solar variations. For this reason, we discount the idea that unpredictable chaotic influences completely govern the climatic system. We will now review three additional forcing functions for climate, specifically volcanic aerosols, anthropogenic aerosols, and greenhouse gas warming. Modern climatologists consider these three forcings the most popular for explaining observed climatic changes. Yet just as the sun/climate connections can be harshly criticized, so can these three ideas, and we will treat these theories with skepticism. We will strive to adopt this same skeptical attitude for solar forcing of climate again in chapter 13.