Tuesday, October 26, 2010

A little bit goes a long way

Nearly every attempt to undermine the well-established climate science that clearly demonstrate how human activities are altering climate is based on a speck of logic either completely misapplied or drowned in errors (if not both). Perhaps the most common is in saying climate has changed naturally in the past and from that asserting that humans cannot be responsible for current changes. That is bad reasoning, just like saying arson is not possible because fires have long occurred for natural reasons.

Thinksee Nosebetter though is all about erroneously believing climate science is an easily toppled house of cards. As noted before, another one of his favorites is that CO2 makes up such a tiny amount of the atmosphere. Again, there are fundamental flaws in that thinking. But some try to build on that by saying that water vapor is a greenhouse gas that is much more abundant in the atmosphere than CO2, so if any greenhouse gas is causing warming it must be water vapor and not CO2. The short answer to that claim is that, unlike CO2 which functions as both a forcing and a feedback in climate change, water vapor only works as a feedback.

Expanding on that a bit, it means water vapor content of the atmosphere depends on the state of the climate. This is because water vapor is readily condensable from our atmosphere - e.g., it gets cold enough, and the water vapor condenses into liquid water that precipitates out of the atmosphere. If you could magically alter the water vapor content of the atmosphere, it would basically return to where it was content-wise before the change in days. If you could magically alter the CO2 content (like we are doing now, except instanteously), such a snap-back would not occur.

Recent research has further refined the quantification of the different components of the greenhouse effect such as CO2 and water vapor. The analogy used is that CO2 is the thermostat for global temperature - a small piece of the building that controls a larger piece all working to drive the climate inside. Water vapor and liquid water clouds could not maintain the climate we know by themselves. They require the smaller but essential effect of the non-condensable greenhouse gases led by CO2 to be able to do what they do.

Though not perfect, the CO2-thermostat analogy is very good. A similar analogy would be with CO2 and the accelerator pedal of an automobile. The level of the pedal determines how much gas the engine gets and thus how fast the vehicle goes. Small components of systems can drive large effects. A few generals can determine the actions of many thousands of soldiers. Hundreds of legislators can set rules for millions of citizens. And distressingly a few misleaders can warp the understanding of climate science for a great many.

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