Global Warming Researchers Reverse Stance on Storm Intensity Theory

Blog: Science Global Warming Researchers Reverse
Stance on Storm Intensity Theory
Michael Asher (Blog) – April 13, 2008 3:56 AM

The image of a hurricane-spawning smokestack was
used to promote the film, An Inconvenient Truth.

Author of the theory that global warming breeds
stronger hurricanes recants his view

Noted Hurricane Expert Kerry Emanuel has publicly
reversed his stance on the impact of Global
Warming on Hurricanes. Saying “The models are
telling us something quite different from what
nature seems to be telling us,” Emanuel has
released new research indicating that even in a
rapidly warming world, hurricane frequency and
intensity will not be substantially affected.

“The results surprised me,” says Emanuel, one of
the media’s most quoted figures on the topic.

The view that global warming has limited impact
on hurricane strength has been previously
reported in numerous DailyTech articles.

Emanuel, professor of Atmospheric Science at MIT,
is the author of numerous books and research
papers on climate change. For over twenty years,
he has argued that global warming breeds more
frequent and stronger storms.  In fact, his 1987
paper is often cited as the first appearance of
the theory itself.

His 2005 research — published just one month
before Hurricane Katrina struck — made world
headlines, and was heralded as the “final proof”
that Global Warming was already having severe
impacts on daily lives.  Overnight, Emanuel
became a media darling.  The following year, Time
Magazine named him to their “100 People Who Shape
Our World” list.

In 2006, Al Gore used an image of a smokestack
spawning a hurricane to promote his movie, An
Inconvenient Truth.

Emanuel’s newest work, co-authored with two other
researchers, simulates hurricane conditions
nearly 200 years in the future. The research —
the first to mesh global climate models with
small-scale high-resolution simulations of
individual storms — found that while storm
strength rises slightly in some areas, it falls
in others — and the total number of worldwide
storms actually declines slightly.

Emanuel’s reversal is certain to reverberate
through political circles as well; many
politicians and candidates are using the
hurricane threat to compel action on climate
change.
Abstract View

Volume 89, Issue 3 (March 2008)
Bulletin of the American Meteorological Society

Article: pp. 347-367 | Abstract | PDF (2.86M)
Hurricanes and Global Warming: Results from Downscaling IPCC AR4 Simulations

Kerry Emanuel, Ragoth Sundararajan, and John Williams

Program in Atmospheres, Oceans, and Climate,
Massachusetts Institute of Technology, Cambridge,
Massachusetts

ABSTRACT

Changes in tropical cyclone activity are among
the more potentially consequential results of
global climate change, and it is therefore of
considerable interest to understand how
anthropogenic climate change may affect such
storms. Global climate models are currently used
to estimate future climate change, but the
current generation of models lacks the horizontal
resolution necessary to resolve the intense inner
core of tropical cyclones. Here we review a new
technique for inferring tropical cyclone
climatology from the output of global models,
extend it to predict genesis climatologies
(rather than relying on historical climatology),
and apply it to current and future climate states
simulated by a suite of global models developed
in support of the most recent Intergovernmental
Panel on Climate Change report. This new
technique attacks the horizontal resolution
problem by using a specialized, coupled
ocean-atmosphere hurricane model phrased in
angular momentum coordinates, which provide a
high resolution of the core at low cost. This
model is run along each of 2,000 storm tracks
generated using an advection-and-beta model,
which is, in turn, driven by large-scale winds
derived from the global models. In an extension
to this method, tracks are initiated by randomly
seeding large areas of the tropics with weak
vortices and then allowing the intensity model to
determine their survival, based on large-scale
environmental conditions. We show that this
method is largely successful in reproducing the
observed seasonal cycle and interannual
variability of tropical cyclones in the present
climate, and that it is more modestly successful
in simulating their spatial distribution. When
applied to simulations of global climate with
double the present concentration of carbon
dioxide, this method predicts substantial changes
and geographic shifts in tropical cyclone
activity, but with much variation among the
global climate models used. Basinwide power
dissipation and storm intensity generally
increase with global warming, but the results
vary from model to model and from basin to basin.
Storm frequency decreases in the Southern
Hemisphere and north Indian Ocean, increases in
the western North Pacific, and is indeterminate
elsewhere. We demonstrate that in these
simulations, the change in tropical cyclone
activity is greatly influenced by the increasing
difference between the moist entropy of the
boundary layer and that of the middle troposphere
as the climate warms.

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