lotus

previous page: 39 How does El Nino-Southern Oscillation affect tropical cyclone activity around the globe?
  
page up: Storms FAQ
  
next page: 41 Are we getting stronger and more frequent hurricanes, typhoons, and tropical cyclones in the last several years?

40 What may happen with tropical cyclone activity in a 2xCO2 world?




Description

This article is from the Storms FAQ, by Chris Landsea landsea@aoml.noaa.gov with numerous contributions by others.

40 What may happen with tropical cyclone activity in a 2xCO2 world?

Two impacts of anthropogenic climate change due to increasing amounts of
"greenhouse" gases that may occur (Houghton et al., 1990, 1992) are
increased tropical sea surface temperatures (moderate confidence) and
increased tropical rainfall associated with a slightly stronger inter-
tropical convergence zone (ITCZ) (moderate/low confidence). Because of
these possible changes, there have been many suggestions based upon global
circulation and theoretical modeling studies that increases may occur in the
frequency (AMS Council and UCAR Board of Trustees, 1988; Houghton et al.,
1990; Broccoli and Manabe, 1990; Ryan et al., 1992; Haarsma et al., 1993),
area of occurrence (Houghton et al., 1990; Ryan et al., 1992), mean
intensity (AMS Council and UCAR Board of Trustees, 1988; Haarsma et al.,
1993), and maximum intensity (Emanuel, 1987; AMS Council and UCAR Board of
Trustees, 1988; Houghton et al., 1990; Haarsma et al., 1993; Bengtsson et
al., 1994) of tropical cyclones. In contrast, there have been some
conclusions that decreases in frequency may result (Broccoli and Manabe
1990; Bengtsson et al., 1994). One report (Leggett, 1994) has suggested
that increased tropical cyclone incidence and severity have already taken
place, but provided no quantitative evidence.

Any changes in tropical cyclone activity are intrinsically tied in with
large-scale changes in the tropical atmosphere. One key feature that
has been focused upon has been possible changes in sea surface
temperatures (SSTs). But SSTs by themselves cannot be considered without
corresponding information regarding the moisture and stability in the
tropical troposphere. What has been identified in the current climate
as being necessary for genesis and maintenance for tropical cyclones
(e.g. SSTs of at least 80F or 26.5C) might change in a 2xCO2 world
because of possible changes in the moisture and/or stability.

Additionally, besides the thermodynamic variables, changes in the tropical
dynamics will also play a big role in determining changes in tropical
cyclone activity. For example, if the vertical wind shear over the
tropical North Atlantic decreased (increased) during the hurricane season
in a 2xCO2 world, then we would see a significant increase (decrease) in
activity. Another large unknown is how the monsoonal circulations may
change. If the monsoons became more active, then it may be possible
that more tropical cyclones in the oceanic monsoon regions might result.

One last final wild card in all of this is how the El Nino-Southern
Oscillation (ENSO) may change in a 2xCO2 world, as ENSO is the largest
single factor controlling year-to-year variability of tropical cyclones
globally - see sections G2) and F2). If the warm phase of ENSO (the "El
Nino" events) occurred more often and/or with more intensity, then the
inhabitants along the Atlantic basin and Australia would have fewer
tropical cyclones to worry about. But people living in Hawaii and in the
South Central Pacific would have more storms to deal with. The reverse
would be true if the cold phase (or "La Nina") became more prevalent.

Overall, it is difficult to assess globally how changes of tropical cyclone
intensities (both the mean and the maximum), frequencies, and area of
occurrence may change in a 2xCO2 world. It may very well turn out that
changes around the globe may not be consistent, with some regions receiving
more activity while others getting less. Certainly, this is an area of
research that needs to continue until more definitive answers are found.

 

Continue to:













TOP
previous page: 39 How does El Nino-Southern Oscillation affect tropical cyclone activity around the globe?
  
page up: Storms FAQ
  
next page: 41 Are we getting stronger and more frequent hurricanes, typhoons, and tropical cyclones in the last several years?