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   Newest Estimate of Global Warming & Hurricanes

  The most recent data indicate (conservatively) that global warming has increased hurricane destructiveness more than 45% in recent years. The data shown here relate hurricane strength to warmer waters but not directly to global warming. They show that total hurricane energy is very sensitive to warmer water temperatures. This sensitivity is greater than was expected. If sea surface temperature has increased due to global warming, as is generally believed, there is no escaping the fact that global warming has contributed to the energy of recent hurricanes.

For political reasons, NOAA admits that warmer waters have been the main factor in increased hurricane energy, but issues statements (read translation) designed to make the public believe there is no connection to global warming, although the evidence points in the opposite direction.
Stoft  2005 09 hurricane global warming
Data from Dr. Kerry Emanuel have been updated since the publication of his letter in Nature.  Statistical analysis by Dr. Stoft of zFacts.com.
Destructiveness Increases Quickly with Sea Temperature
The graph above shows the first statistical estimate of the impact of global warming on Atlantic hurricanes in recent years. The average expected effect is an increase in hurricane intensity for the years 2002-2004 (averaged in the point labeled "2003") of 96%.  That is, without global warming, the average intensity of hurricanes in those years would be expected to be about half what we experienced.

The points in the graph are annual average sea surface temperatures and a hurricane energy indices for the years 1945-2003. The points are those used in the graph (figure 1 - North Atlantic) published by Dr. Emanuel in Nature, August 2005, updated with a bias correction suggested by Chris Landsea, head of NOAA's Hurricane Reanalysis Project.

The red curve shows the best-fit relationship between annual sea surface temperatures and total annual hurricane energy. It measures what is expected on average given a particular sea surface temperature. This curve does not depend on what caused the sea temperatures—it is not based on any assumption of global warming. But, because sea surface temperatures have increased (on average) as a result of global warming, and are expected to increase further (again, on average), the curve can be used to estimate increases in hurricane intensity (again, on average).

For example, the "2003" (2002-2004 average) sea surface temperature was approximately 27.7 degrees Centigrade. North Atlantic sea temperatures have risen by 0.5° C due to long-term global warming—this is the consensus estimate for the global increase in sea surface temperatures since the 1800s. Thus, without global warming the 2002-2004 average temperature would be expected to be 0.5 degrees C less—approximately 27.2 degrees C. Over that range (indicated by the vertical lines on the chart) the red curve shows an increase in hurricane energy (and destructiveness) from 0.97 to 1.90. That's a 96% increase that can be attributed to the effects of global warming.

This is an average prediction. Actual yearly outcomes varied, and we will never know precisely what would have happened without global warming. Additional uncertainties are introduced by the "margin of error" in fitting the curve (since, like a voter survey, it is based on a limited sample) and by the "margin of error" that can be attributed to the 0.5 degree C estimate of global warming to date.

  How Accurate is the Trend Line?
A statistical test shows the lower "Rejected Trend" is 95% sure to be too low, and even it would indicate a 45% increase in hurricane destructiveness.

The data points clearly rise from left to right, so there can be no doubt the best fitting trend line slopes up. But perhaps the Atlantic just had bad hurricane luck during warm years and good hurricane luck during cooler years, and all the trend line is picking up is this luck?  The point of statistics is to tell us how much to trust our estimates and what is the chance that the things we see are just due to luck.

The lower line was choosen to be exactly half as steep as the actual trend line. It was tested statistically with an "F-test" which found less than a 5% chance that bad luck has fooled us and things are really as good as the lower trend line.

If global warming has warmed the Atlantic just 0.5° C, there is a 95% chance that it has increased average annual hurricane destructiveness by more than 45% (Half a degree C is less than 1 degree Farenheit.)

Katrina Cause? Did Global Warming Cause Katrina?
NOAA Decoded NOAA on Hurricanes and Global Warming

http://zfacts.com/p/120.html | 01/18/12 07:16 GMT
Modified: Tue, 22 Apr 2008 17:26:39 GMT
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