Global warming reduces hurricanes?

by Joe Archive on May 24, 2008

Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions – a href=””Knutson et. al; Nature Geoscience – subscription required :(/abr /br /Changes in large-scale climate projected by IPCC used to force regional Atlantic Basin Model to assess hurricane frequency changes that might be driven by climate /br /A high-resolution simulation of the present-day Atlantic basin is nudged on large spatial scales to match the reanalysis data (numerical realizations of the global atmosphere that assimilate the many observations that exist into the models).br /Hurricanes simulated by the model are not as intense as observed – probably a result of insufficient resolution. Storm tracks in the model are /br /The warm-climate runs show a general reduction in storm frequency. Will Global Warming reduce the hurricanes we have to deal with?br /br /I am not so sure – I see a problem with their methodology: the “warm climate” simulations are a simple rerun of the present day simulations with the day to day and year to year variations unchanged, with just the mean temperature (and probably moisture) profiles increased as predicted by the climate projection /br /They thus make the implicit assumption that the climate variability will be unchanged under global warming, an assumption that seems unlikely and is generally not found to be true in climate /br /Unfortunately, future variability is a hard thing to account for – the current models are not sufficiently accurate that I would trust any specific details of /br /Another observation is that near storm rainfall is increased – rainfall comes from condensation, which releases latent heat – a source of energy for the hurricanes – so the hurricanes should perhaps be stronger on average. Even with a reduced frequency, if the number of extreme hurricanes increases, then we are probably worse off, both financially and environmentally – the global ecosystems will have evolved “assuming” a certain distribution of hurricane intensities in an average year – changes to this distribution could change many things: mixing of nutrients and/or silt throughout the oceans, rainfall amounts in rivers and lakes in regions near the eastern coasts of the continents that tend to be fed by the precipitation from the storm systems that form out the decaying /br /These are complicated questions that I don’t know enough to /br /I suspect that if this experiment was rerun with an increased warm climate variability, the results might be quite different.

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