I Thought Global Warming CausedMore Hurricanes...

Discussion in 'Environment' started by KMAN, Nov 6, 2008.

  1. KMAN
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    KMAN Senior Member

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  2. Old Rocks
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    Old Rocks Diamond Member

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    For more of this article;


    Anthropogenic Effects on Tropical Cyclone Activity

    Anthropogenic Effects on Tropical Cyclone Activity
    (Revised January, 2006)
    Kerry Emanuel
    Program in Atmospheres, Oceans, and Climate Click Here to return to Kerry Emanuel’s Home page.
    Massachusetts Institute of Technology
    Cambridge, MA 02139, USA

    Part I: Frequently asked questions

    Part II: Essay



    I. Frequently Asked Questions about Global Warming and Hurricanes



    1.) Q: Is global warming causing more hurricanes?

    A: No. The global, annual frequency of tropical cyclones (the generic, meteorological term for the storm that is called a tropical storm or hurricane in the Atlantic region) is about 90, plus or minus 10. There is no indication whatsoever of a long-term trend in this number.

    2.) Q: But I’ve noticed that there seem to have been lots more hurricanes, beginning around 1995.

    A: You probably live in North America, Central America, or Europe and are talking about hurricanes in the North Atlantic. (It’s important to remember that only 11% of all hurricanes occur in the Atlantic, the rest are in the Pacific and Indian Oceans.) There has been a large upswing in the frequency of Atlantic hurricanes, beginning in 1995. This corresponds to an upswing in tropical North Atlantic sea surface temperature, which is very likely a response to increasing anthropogenic greenhouse gases. It is important to note that the late summer and early fall tropical Atlantic sea surface temperature closely follows the Northern Hemisphere mean surface temperature (including land), which makes it unlikely that regional Atlantic climate phenomena are affecting tropical sea surface temperatures ( and thereby affecting hurricanes) on time scales of more than a few years. In particular, there is no evidence for "natural cycles" of either Atlantic hurricane activity or tropical Atlantic sea surface temperature.

    3.) Q: Is the intensity of hurricanes increasing with time?

    A: There is some evidence that it is. Records of hurricane activity worldwide show an upswing of both the maximum wind speed in and the duration of hurricanes. The energy released by the average hurricane (again considering all hurricanes worldwide) seems to have increased by around 70% in the past 30 years or so, corresponding to about a 15% increase in the maximum wind speed and a 60% increase in storm lifetime.

    4.) Q: But aren’t there lots of errors in the hurricane record?

    A: Yes, there are. Reliable records of wind speeds in hurricanes over the open ocean go back only to around 1950, when aircraft reconnaissance of hurricanes began over the North Atlantic and western North Pacific; before that, the only good measurements of wind speed were made when hurricanes made landfall or passed over islands or ships with measuring equipment. Unfortunately, methods of measuring or estimating wind speed from aircraft have evolved over time, and these changes were not always well documented. Since about 1980, there are wind estimates for all hurricanes globally, based on satellite images, but these are not as good as aircraft measurements.

    5.) Q: Then how can you determine trends with such data?

    A: Fortunately, the means of estimating the central surface pressure in hurricanes have remained fairly constant with time. In practice, central pressure is well correlated with maximum wind speed, and therefore can be used to detect changes in the way winds were estimated from pressures. Also, in a large enough sample of events, the wind speeds are well correlated with a quantity call the “potential intensity”, which is a function of the temperature of both the ocean and atmosphere. We have fairly good records of the information needed to calculate potential intensity, and so can compare estimated wind speeds with estimated potential intensity for large enough samples. This is another check on the quality of the wind estimates. Even in the Southern Hemisphere, where there have never been aircraft observations of hurricanes, the satellite-based estimates compare well with estimates of potential intensity.
     
  3. Chris
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    Chris Gold Member

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    We are in the down part of the solar cycle and the Southern Ocsillation. It will pick up as those two cycles move up in the next few years.
     

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