Bill Menke's BLOG Page: Hurricane Katrina not due to Global Warming
The idea that global warming - caused by greenhouse warming of the earth as human beings increase atmospheric carbon dioxide by burning coal and oil - can potentially have an impact on the severity of hurricanes is legitimate. Hurricanes are driven by warm ocean waters. It makes sense that their strength would increase as global warming drives up ocean temperatures.
The temperature of the world's surface - including the oceans - has increased about 0.7 deg C since 1900. Most climatologists believe that the recent increase is anthopogenically driven, but the case is hard to prove given the current imprecision in climate modeling. The 0.7 increase is significant, but it is small compared to both the year-to-year variability observed in any small region, such as a continent or ocean (some of which is related to the El Nino and North Atlantic climate oscillations) and it is also small compared to natural century-long temperature variations that have occured over the last few thousand years. So while global change may arguably be having an effect on hurricane severity, natural variability is simultaneously having a much larger effect. Category 5 hurricanes like Katrina would happen even in the absence of global warming. The Category 5 storm that hit the Florida Keys in 1935 - a period before much global warming had occured - is a case in point. Attempts to assess whether the number of severe hurricanes has increased over the last century have been hampered by the relatively poor data available for the early part of the century, but no statistically-significant trend has been observed.One common fallacy is to equate hurricane damage with hurricane severity. These two measures are not the same! Hurricanes only do damage if and when they make landfall in a populated region. Many Catagory 4 and 5 hurricanes go unnoticed by the American public because they do not make landfall, make landfall in an uninhabited region, or - to our shame - damage some poor Carribean country about which most of us have never even heard. The unnamed Category 5 hurricane of August 1932, which stayed well-offshore the US, but which clipped the Bahamas, is an example.
In the US, hurricane damage has been increasing with time, simply because there is more to damage! The US Gulf Coast is really quite a bit more built up than it was in 1900.