Human-caused greenhouse gasses heating up hurricane season

Human-generated greenhouse gasses are a factor in the increasing frequency, intensity and duration of hurricanes in the Atlantic, according to a paper presented at an October 2006 RMS hurricane symposium.The paper, “Principal Drivers of Multi-Year Hurricane Activity,” was presented by MIT resercher Kerry Emanuel at the Proceedings of the 2006 RMS Hurricane Eyewall Symposium in New York City.”There is little evidence for natural, multi-decadal ‘cycles’ in the sea-surface temperature between the late summer and early fall, and multi-decadal cycles in tropical cyclone activity in the Atlantic are being contested in the current scientific literature,” Emanuel concludes in his paper. “The long-term trends and variability have probably arisen from anthropogenically forced [i.e. human generated] climate change.”Emanuel notes the best observations of storms exist for the Atlantic, even though they constitute only 11% of global tropical cyclone activity. “Uniquely in the Atlantic, the frequency of storms is correlated well with tropical sea-surface temperatures,” the paper notes.Emanuel’s paper says the Potential Intensity (PI) a measure of the outer limit of hurricane wind speeds has been increasing markedly for at least the last decade in the Atlantic, “largely owing to an increase in sea-surface temperature as well as to a decrease in the temperature of the upper atmosphere.””Greenhouse gases and associated radiative forcing (i.e. amplification of the effect of the Sun) have been increasing, but other anthropogenic factors, such as sulfate aerosols that reflect solar radiation and exert a cooling effect, together with additional natural forcings, have also contributed to the observed variability in temperatures,” Emanuel notes.The author further notes that hurricanes “are almost perfect Carnot heat engines that run on the thermodynamic disequilibrium, caused by the greenhouse effect, between the tropical ocean and atmosphere.”Although there has been no long-term change in the global frequency of tropical cyclones, average intensity and duration seem to have increased in concert with sea-surface temperatures of the tropical oceans.Changes in the tropical sea-surface temperature “should be sensitive to rises in the concentrations of greenhouse gases in the atmosphere,” the author says. “However, the magnitude of the increase in sea-surface temperature that should theoretically result from the present injection of anthropogenic greenhouse gases into the atmosphere, is unclear due to a lack of certainty in the understanding of feedbacks in the climate system.”