Hurricanes and Climate Change
Is global warming contributing to an increase in the number and intensity of hurricanes in the Atlantic Basin?
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The first, and more traditional approach, starts with the assumption that hurricane favorable conditions in the Atlantic Basin are related to long term ocean climate factors, the two most important being the North Atlantic Oscillation and the Southern Oscillation.
After watching hurricane coverage on television during the past couple of years, most Americans are generally aware that the combination of Pacific and Atlantic Ocean water temperatures and wind patterns produce what researchers call multi-decadal climate variability, or medium term weather patterns. According to the mainstream approach, the number and intensity of hurricanes in the Atlantic Basin increase during La Nina years (cold water pattern that produces less upper atmosphere winds) when the North Atlantic Oscillation produces above average sea surface temperatures.
NOAA adopted this explanatory approach for describing the record breaking 2005 hurricane season that saw Hurricane Katrina wreck havoc on New Orleans and the surrounding coastal communities. (see NOAA Attributes Recent Increase in Hurricane Activity to Naturally Occurring Multi-Decadal Climate Variability.
The historical evidence guiding their conclusions was straight forward. Active hurricane seasons in the Atlantic Basin are not a new phenomena but rather part of a larger weather pattern that can be seen by examining hurricane statistics (see Atlantic Basin Hurricanes 1850-2006.
There are multiple ways to look at the raw data to tell a hurricane story. The fifteen hurricanes listed for 2005, eclipsed the old record, twelve hurricanes in 1969. Knowing that fact probably does not convince most Americans living during the Apollo 11 moon landing that space flight pokes holes in the atmosphere and contributes to record breaking hurricane seasons.
The statistics also show 82 hurricanes formed during the 1996-2005 ten year period. Apart from using the 1997-2006 ten year data, the second highest decadal hurricane count, 70, occurred in the ten year period following World War II, 1947-1956. You have to go back to the post-Civil War era, 1878-1887, to find the third highest decadal hurricane count, 68.
Since tools used to measure wind speeds for hurricanes have changed over time, long term statistical comparisons of hurricane formation can not be considered perfect. Without any further statistical analysis, the most one might readily conclude from an evaluation of long term trends is that absent any potential global warming effect, Atlantic Basin hurricane history shows hurricane formation variability over time.
Theories assuming that climate change contributes, or will contribute, to either more hurricanes or more intense hurricanes, do not necessarily discount the prevailing decadal climate variability theories. (see Global Warming and Hurricanes).
It is probably more accurate to say that the second group of theories adds an additional hypothesis to the decadal theories. In general terms the climate change based theories can be presented as follows: Assuming that Atlantic Basin hurricane formation varies over time, and assuming that climate change increases sea surface temperatures, it is equally reasonable to hypothesize that because sea surface temperature is one factor affecting hurricane formation, anthropogenic factors increasing sea surface temperatures bring with them an increased probability of causing either more hurricanes or more intense hurricanes. Scientists are currently working with models to either demonstrate or falsify the hypothesis.
Politics accounts for the remainder of the climate change and hurricane story. James Elsner Geography professor from Florida State University, reviews the most recent political debates and concludes, "Neither side is completely wrong and both would do well to study the full breadth of literature."
© 2007. Patricia A. Michaels. All Rights Reserved.