Future Storminess in a Warmer World

James B. Elsner, Earl and Sophia Shaw Professor & Chair, Geography Department

February 19th, 2018

Who Am I?

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Who am I?

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Who am I?

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Course Themes

  • Heat & hurricanes: Connecting the dots.
  • Rising hurricane damage.
  • Fewer but stronger.
  • Fewer days but bigger outbreaks.
  • More tornado energy.
  • Who survives? Tornado vulnerability.

Graphs, reproducible research, myweb.fsu.edu/jelsner/Day1.html

  • Theory: Limited. No theory of climate. Hurricanes are still a mystery.
  • Models: Miss the details.
  • Data: Never enough. Quality.

Combine what we know (thermodynamics, statistics) with the best available data.

Thermodynamics: Maximum Potential Intensity (MPI)

\[ \hbox{MPI} \sim \frac{\hbox{SST}}{T_o}\hbox{BL}_{f}(\hbox{SST}) \]

  • MPI: highest wind speed (rotating).
  • SST: Sea-Surface Temperature.
  • \( T_o \): temperature above the hurricane.
  • BL\( _{f} \)(SST): heat exchange between air and sea. Fluxes depend on SST.

Statistics: Limiting Intensity (LI)

Extreme Value Theory (EVT)

Fastest wind (m/s) from 10 hurricanes.

  • 34, 44, 57, 33, 68, 38, 42, 71, 61, 49

Order the values from lowest to highest.

  • 33, 34, 38, 42, 44, 49, 57, 61, 68, 71

20% of the hurricanes have winds exceeding 61 m/s & 10% have winds exceeding 68 m/s. EVT uses these quantile winds to work out a theoretical highest, which we will call the limiting intensity (LI).

  • Limiting intensity (LI) is a statistical estimate that we can use to compare with the theoretical maximum potential intensity (MPI).
  • How should we make this comparison?
  • Absolute values of LI are not as important as how LI changes with ocean temperature (SST).
  • How can we estimate how LI changes with SST?

Why Is This Important?

Summary

  • Future hurricanes? Combining theory with data.
  • The strongest hurricanes will likely get stronger at about 8 m/s per degree of ocean warming.
  • Or about 1 m/s per decade at the current rate.
  • This translates to about a 5% increase in loss per decade independent of exposure.

Next Week: Fewer but stronger

Next Week: Tornadoes