[Vision2020] 9-5-17 Realclimate "Why extremes are expected to change with a global warming"

[Ted Moffett]

http://www.realclimate.org/index.php/archives/2017/09/
why-extremes-are-expected-to-change-with-a-global-warming/#more-20607

Article partially pasted in:
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Vision2020 Post: Ted Moffett
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Rasmus E. Benestad
http://www.realclimate.org/index.php/archives/2004/12/rasmus-e-benestad/
<http://www.realclimate.org/images//natl-tc.png>

Fig. 2 shows predictions with a simple model that predicts the number of
tropical cyclones (*NTC* and *n*) in the North Atlantic based on the area
of warm sea surface (*A*) and the NINO3.4 index. It was created in R using
the script tropicalcyclones.R
<http://www.realclimate.org/images//tropicalcyclones.txt> which also
retrieves the data. The model was calibrated over the period 1900-1960, and
the predictions provide reasonable similar evolution of the North-Atlantic
tropical cyclones outside this period. (PDF-version
<http://www.realclimate.org/images//natl-tc.pdf>).

The analysis in Fig. 2 shows a crude prediction of the *number of tropical
cyclones* (*n*) in the North

Atlantic based on the *area of warm ocean surface* (*A*), and we see a
roughly similar trend in these

predictions as in the HURDAT2 tropical cyclone record.

One caveat with such empirical studies, however, is that the data record is
incomplete and there is a

risk that the analysis presents a false picture.

Nevertheless, the IPCC AR5 presents an outlook of

increasing extreme precipitation in tropical cyclones making landfall (p.
106, Table TS.2), which is

relevant for the flooding connected to Harvey.

Flooding may also become more severe from changes

in the landscape, as explained by John Vidal in an article in the Guardian
<https://www.theguardian.com/world/2017/sep/02/flood-waters-rising-urban-development-climate-change>
.

I think Joanna Walters’ article about extremes and climate change describes
the current situation well,

and we should not be too surprised.

A change in the pdf reflects a climate change, and in most cases

its range and tails tend to follow the part of the curve that represents
the more common conditions.

We must assume that it is only the exceptional cases where the tails of the
pdf are unaffected.

Furthermore, an increase in the number of tropical cyclones would increase
the number of more cases

with extreme rainfall
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