Don't blame hurricanes on global temperatures
Published: Monday, August 1, 2005 at 6:01 a.m.
Last Modified: Sunday, July 31, 2005 at 10:28 p.m.
There is some disagreement among climate scientists on the potential impact of global climate change on future hurricanes in the Atlantic Ocean. Last year, claims were made that the frequency of hurricanes will increase due to global climate change.
For example, after Hurricanes Bonnie, Charley and Frances hit Florida in 2004, Prime Minister Tony Blair of England and prominent American scientists told the world that the hurricanes were due to global warming. Luckily, scientists who actually regularly study hurricanes quickly responded with the facts, and for once the misinformation was curbed quickly and effectively.
But, now the alarmists are at it again claiming that global warming will increase the intensity of hurricanes. Don't worry, readers. There is absolutely no scientific support or correlation of hurricane intensity or hurricane frequency with global warming.
Hurricane scientists and experts actually believe that variations in the Atlantic Ocean Conveyer, not global temperatures, determine the frequency of hurricanes. It is predicted that we will see an increase in the number of Atlantic hurricanes for the next 10-15 years compared to recent years. This is nothing new - the last peak occurred between 1930-1970.
What is the Atlantic Ocean Conveyer and why does it affect hurricanes?
In the North Atlantic, in the Labrador and Gin Sea, water is cooled and sinks to the bottom in winter. The sinking water is replaced by warm Gulf Stream water that leaves the North Carolina coast and proceeds toward the Northeast to lreland and Norway. The Gulf Stream draws water from the South Atlantic. The rest of the conveyer belt is in the other oceans but the Atlantic portion is the dominant feature.
This oceanic phenomenon varies and changes the sea surface temperatures. When it is strong - 1930-1970 and 1995-2000 to now - there are more Atlantic hurricanes. When it is weak - 1905-1925 and 1975-1994 - the hurricane season is mild.
And what about intensity? Hurricanes have to keep moving or they die by upwelling the cold water below the warmer sea surface temperatures. Hurricane Mitch, in 1998, is a textbook example of this: Mitch stalled off Honduras when it lost its upper atmospheric steering currents. This caused it to die and drop over 6 feet of rain on the poor folks in Honduras and Nicaragua.
A hurricane will also grow stronger as it moves over water warmer than 80 F (26.5 C). This is why some people believe that global warming will increase hurricane intensity, but there are no scientific calculations that show the areas of water this warm increasing in size.
However, if one graphs the ocean environment for Category 3, 4 and 5 storms, there is no difference in ocean surface temperatures for tropical storms and category 1 and 2 storms.
What's more, the scientific literature documents that the western Atlantic off Africa is the prime breeding ground for the stronger storms - and many of those stronger storms never make it to landfall.
While it is tempting to blame the frequency or intensity of hurricanes on man, we all must remember how variable nature is - and specifically in this case, the effect of natural variations on hurricane intensity and frequency is extremely higher than the possibility of man's interference.
James O'Brien is Florida's state climatologist and professor of meteorology and oceanography at Florida State University.
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