In the wake of the disaster caused by Tropical Storm Sandy, various allies of the Obama campaign have rushed to claim that the event was caused by anthropogenic global warming, thereby justifying the president’s program of crushing the economy with regressive carbon taxes, a supposedly necessary measure to prevent future bad weather. In fact, there is no scientific basis, either empirical or theoretical, to justify such claims.
Weather systems are natural heat engines, and like all other heat engines, both natural and artificial, they are driven not by temperature per se, but by differences in temperature between one location and another. A professor at my old university once illustrated this principle in striking fashion by showing that he could make a car run on liquid nitrogen, using the temperature difference between the ultra-cold fluid and the merely cool ambient Seattle air to derive strong motive power. Similarly in nature, temperature differences, such as that between the warming land and the cold sea at sunrise, create wind, and under the right conditions, can form powerful windstorm systems. Where temperatures are uniform, there is no motive power, regardless of how hot conditions may be.
The Earth is significantly warmed by a greenhouse effect caused largely by water vapor in its atmosphere. But because warm air can hold much more water vapor than cold air, water-vapor greenhousing works more effectively where it is warm than where it is cold, and thus serves to increase the temperature differences between warm regions and cold regions, as well as between day and night. In contrast, carbon dioxide spreads evenly in the atmosphere regardless of local temperature, and thus delivers its insulative warming effect to those water-vapor-poor regions which benefit from it the most. And while it also adds insulation to hot places as well, the marginal effect of the addition is much greater for the have-nots than the haves. (To understand this, just consider the benefit of putting one flannel shirt on a naked chest on a cold day to putting a second shirt over that. The difference between having one shirt and none is much greater than that between having one shirt or two.)
For this reason, it is widely understood that carbon dioxide–driven global warming would have the effect of reducing temperature difference among different parts of the Earth, and therefore reducing the motive force for creating major wind systems. This fact is even acknowledged by the generally global-warming-alarmist U.N. Intergovernmental Panel of Climate Change (IPCC) which states as much in its recent report (page 11, emphasis in original):
It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged. [3.4.4]
There is medium confidence that there will be a reduction in the number of extratropical cyclones averaged over each hemisphere.