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Are Hurricanes Stronger Due To Global Warming?
Let me first tell you that there is no connection between Hurricane Katrina and global warming. Damage from Katrina in New Orleans was in large part due to a poor levee system. Although there has been an increase in damage in the United States from huricanes and tropical storms, this is largely due to the increase in coastal populations prone to hurricanes and tropical storms. Although global warming is not the cause of hurricanes, it still may have an influence. Consider this, warm water is the fuel of hurricanes. With warmer water the result should be stronger hurricanes. It turns out that globally hurricanes have had a large increase in total power generated. That's the conclusions from research by Kerry Emanuel, professor of meteorology at M.I.T. (1). Emanuel also mentions that in the past 30 years hurricanes have increased in max wind speed and duration (keep in mind that's a global average and the Atlantic only represent 11% of hurricanes world-wide). All of this correlates well to the warmer sea surface temperatures as well (1). However, this research makes no claims about an increased frequency in hurricanes and points out that it is difficult to predict the increase in potential intensity of hurricanes because of the uncertainties surrounding global warming predictions (click here for "How Accurate Are Global Warming Predictions"). But the statistics from Emanuel's research show an increase in the intensity of hurricanes and the duration of hurricanes world-wide in the past 30 years. So, global warming has warmed the oceans and that has in turn created more powerful and longer lasting hurricanes on average across the globe. Makes sense, right? Not so fast my friend! Although this research presents evidence that there may be a global warming influence on hurricanes world-wide, it is certainly not conclusive and in fact that connection was not the goal of this research.
And when it comes to the Atlantic Basin (those are hurricanes that affect the US) there's another theory and it does not involve global warming. In fact, it's the prevailing theory from NOAA (National Oceanic and Atmospheric Administration). The nut meat, if you will, is that instead of global warming causing the warmer oceans, it is simply a natural cycle of warming and cooling in the Atlantic (2). This is a widely accepted trend, in fact Kerry Emanuel the guy I mentioned above, even agrees that when it comes to the Atlantic hurricane activity is mostly not related to global warming (3). What is happening in the Atlantic? According to NOAA, it's all natural. That is, there is a natural cycle called the "tropical multi-decadal signal". This means that there is a cycle of increased or decreased hurricane activity in the Atlantic that last 20 to 30 years or so. There was a lull in activity in the 70's and 80's and then since 1995 the cycle switched to increased tropical storm activity (2). Click here for an article from NOAA on this "multi-decadal" cycle for hurricane activity in the Atlantic.
Why does this happen? We don't know. The trends are apparent when looking back at historical data, but we don't know what triggers this trend and thus can't accurately predict the switching of the trend. There is so much that we don't know about atmosphere and oceans (that's why we need more young meteorologists!). In my opinion global warming is an easier answer, because the answer to "why does it happen" is not "we don't know". That's not to say there is no global warming influence, but I believe that many, many trends in atmospheric science when asked what causes them, the more difficult and often more truthful answer is "we don't know exactly". So, to answer the question posed in the title of this article, if there is a global warming influence on hurricanes, it would be in the intensity and duration but not the frequency of hurricanes on a global scale. One cannot pinpoint one hurricane and discern any global warming influence. But when it comes to the Atlantic basin a natural cycle is likely occurring that is creating an increase in tropical storm activity. So, research will continue, numbers will be crunched, statistics will pile up...and maybe some day we can make a conclusive statement about global warming and it's influence on hurricanes. Note: This article is current as of January 2007 and I will do my best to update information as new research or theories come out in the future. All photos courtesy of NOAA photo library (1) http://wind.mit.edu/~emanuel/anthro2.htm (2) http://www.magazine.noaa.gov/stories/mag184.htm (3) http://www.democracynow.org/article.pl?sid=05/08/29/145206 |
