Tropical cyclones and climate

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Tropical cyclones and climate

• Adam Sobel
• CEI Katrina workshop

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Big Questions from this year

• What made this Atlantic hurricane season so
  hyperactive?
• Is it natural variability, or a secular trend due
  to global warming?
• Are we going to see more and more of these
  disasters in the future?

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2 splashy papers came out this summer
Emanuel 2005, Nature. This picture is for the N.
Atlantic W. Pacific shows same trend
Webster et al. 2005, Science.
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Total global number of storms of gt TS intensity
is not increasing
Webster et al. 2005
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But the Atlantic has indeed been hopping
Now up to 24 this plot made 10/12/05

Figure courtesy of Suzana Camargo, IRI data
from NOAA
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Some caveats on the observations of TC intensity

• Most storms, most of the time, are not being
  observed in situ.
• Since 1970, we have satellite data, but the
  methods of inferring intensity from that are
  empirical and imperfect.
• Before 1970, we have no satellite data, and
  things become still more uncertain.
• The transition at 1970 makes the error
  characteristics discontinuous, so longer-term
  trends are particularly hard to ascertain.

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Physics of climate influence on TCs

• We have a theory for the potential intensity
  (i.e. maximum possible) a TC can reach, given a
  few environmental variables (e.g. SST)
• Combined with climate change predictions, this
  implies an increase in this maximum intensity.
• But most storms dont reach or even come very
  close to their potential intensity, and we dont
  understand very well what controls how close they
  come to it.
• We dont understand the genesis of TCs very
  well, and so have no theory for their number
  (though have some small skill in predicting
  interannual variations using empirical
  statistical models).

Emanuel 1991
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The theory under-predicts the observed increase
in intensity

• Assuming the distribution of TC intensity
  normalized by potential intensity stays constant
  gives a prediction of actual intensity increase
  for the climate warming observed
• This is considerably less than found in the
  recent studies
• There is large natural variability on decadal
  time scales
• All things considered it is far from clear that
  the observed trend is in any large part due to
  climate change

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There is a large upward trend in damage, but it
is almost all due to increasing
coastal development
Pielke and Sarewitz 2005
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US Landfalling Hurricanes, 1851-2004
from C. Landseas Tropical Cyclone
FAQ http//www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.ht
ml

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If you are interested in learning more, come to
our workshop

• Workshop on Tropical Cyclones and Climate
• At IRI (Lamont Campus), March 26-28, 2006
• Organized by Suzana Camargo, AHS, and others
• Sponsored by ADVANCE, IRI, IGERT