Turks and Caicos Islands

frequency in the last 1,500 years based on proxy reconstructions from regional sedimentary evidence
indicate recent levels of Atlantic hurricane activity are anomalously high relative to those of the last one-
and -a -half millennia (Mann et al., 2009).
Climate models are still relatively primitive with respect to representing tropical storms, and this restricts
our ability to determine future changes in frequency or intensity. We can analyse the changes in
background conditions that are conducive to storm formation (boundary conditions) (e.g. Tapiador, 2008),
or apply them to embedded high-resolution models which can credibly simulate tropical storms (e.g.
Knutson and Tuleya, 2004; Emanuel et al., 2008). Regional Climate Models are able to simulate weak
‘cyclone-like’ storm systems that are broadly representative of a storm or hurricane system but are still
considered coarse in scale with respect to modelling hurricanes.
The IPCC AR4 (Meehl et al., 2007) concludes that models are broadly consistent in indicating increases in
precipitation intensity associated with tropical storms (e.g. Knutson and Tuleya, 2004; Knutson et al., 2008;
Chauvin et al., 2006; Hasegawa and Emori, 2005; Tsutsui, 2002). The higher resolution models that
simulate storms more credibly are also broadly consistent in indicating increases in associated peak wind
intensities and mean rainfall (Knutson and Tuleya, 2004; Oouchi et al., 2006). We summarise the projected
changes in wind and precipitation intensities from a selection of these modelling experiments in Table
3.10.1 to give an indication of the magnitude of these changes.
With regards to the frequency of tropical storms in future climate, models are strongly divergent. Several
recent studies (e.g. Vecchi and Sodon, 2007; Bengtssen et al., 2007; Emanuel et al., 2008, Knutson et al.,
2008) have indicated that the frequency of storms may decrease due to decreases in vertical wind shear in
a warmer climate. In several of these studies, intensity of hurricanes still increases despite decreases in
frequency (Emanuel et al., 2008; Knutson et al., 2008). In a recent study of the PRECIS regional climate
model simulations for Central America and the Caribbean, Bezanilla et al., (2009) found that the frequency
of ‘Tropical -Cyclone-like –Vortices’ increases on the Pacific coast of Central America, but decreases on the
Atlantic coast and in the Caribbean.
When interpreting the modelling experiments we should remember that our models remain relatively
primitive with respect to the complex atmospheric processes that are involved in hurricane formation and
development. Hurricanes are particularly sensitive to some of the elements of climate physics that these
models are weakest at representing, and are often only included by statistical parameterisations.
Comparison studies have demonstrated that the choice of parameterisation scheme can exert a strong
influence on the results of the study (e.g. Yoshimura et al., 2006). We should also recognise that the El Niño
Southern Oscillation (ENSO) is a strong and well established influence on Tropical Storm frequency in the
North Atlantic, and explains a large proportion of inter-annual variability in hurricane frequency. This
means that the future frequency of hurricanes in the North Atlantic is likely to be strongly dependent on
whether the climate state becomes more ‘El-Niño-like’, or more ‘La-Niña-like’ – an issue upon which
models are still strongly divided and suffer from significant deficiencies in simulating the fundamental
features of ENSO variability (e.g. Collins et al., 2005).
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