Global warming: what about hurricanes

1
Global warming what about hurricanes?

• Ross Reynolds
• Dept of Meteorology
• The University of Reading
• r.reynolds_at_rdg.ac.uk

2
IPCC Working group I4th Assessment Report

• Based on a range of models, it is likely that
  future tropical cyclones will become more
  intense, with larger peak wind speeds and more
  heavy precipitation associated with the ongoing
  increase of tropical sea surface temperatures.
• There is less confidence in projections of a
  global decrease in the number of tropical
  cyclones.
• The apparent increase in the proportion of very
  intense storms since 1970 in some regions is much
  larger than simulated by current models for that
  period,

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Recipe for hurricane genesis

• Sea surface temperature gt26C (60m)
• Moist mid-troposphere
• Low wind shear 900hPa to 300hPa
• Adequate low-level spin (relative vorticity)
• Unstable atmosphere

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Saffir-Simpson scale

•  
• The Saffir/Simpson Hurricane Scale
• Category
• Definition-Effects
• 1
• Winds 74-95 mph (64-82 kt)No real damage to
  building structures. Damage primarily to
  unanchored mobile homes, shrubbery, and trees.
  Also, some coastal flooding and minor pier
  damage.
• 2
• Winds 96-110 mph (83-95 kt)Some roofing
  material, door, and window damage. Considerable
  damage to vegetation, mobile homes, etc. Flooding
  damages piers and small craft in unprotected
  moorings may break their moorings.
• 3
• Winds 111-130 mph (96-113 kt)Some structural
  damage to small residences and utility buildings,
  with a minor amount of curtainwall failures.
  Mobile homes are destroyed. Flooding near the
  coast destroys smaller structures with larger
  structures damaged by floating debris. Terrain
  may be flooded well inland.
• 4
• Winds 131-155 mph (114-135 kt)More extensive
  curtainwall failures with some complete roof
  structure failure on small residences. Major
  erosion of beach areas. Terrain may be flooded
  well inland.
• 5
• Winds 155 mph (135 kt)Complete roof failure
  on many residences and industrial buildings. Some
  complete building failures with small utility
  buildings blown over or away. Flooding causes
  major damage to lower floors of all structures
  near the shoreline. Massive evacuation of
  residential areas may be required.
•  
• Note A "major" hurricane is classified as
  Category 3 or greater.
• gt

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Hurricane number/days in ocean basins(Webster et
al., 2005)
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Global hurricane intensity(Webster et al., 2005)
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Summer sea surface temperature(Webster et al.,
2005)
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Model v actual anomalies(Santer et al., 2006)
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Role of external forcing(Santer et al., 2006)
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Conclusion

• There is uncertainty re tropical cyclones and
  global warming
• Global data show 30 year trend toward more
  frequent intense hurricanes
• Attribution of causes of trend needed
• Current model estimates of internal climate
  variability cant explain observed SST increase
  in both Atlantic Pacific critical areas
• Unlikely that climate noise can explain large
  observed SST trend in the Atlantic in last
  century that is 3 to 5 times standard deviation
• Over 1906-2005, 84 chance that external forcing
  explains at least 67 of the observed SST
  increase over the Atlantic and Pacific critical
  regions
• Picture more comlicated than just role of SSTs