'Black
Swan' Storms: Extreme Cyclones Linked to Warming Seas
5
December, 2012
SAN
FRANCISCO — A "black swan" cyclone may sound like the
latest comic book hero, but this "extreme of the extremes"
is the result of climate models that suggest global warming will make
future hurricanes more intense.
The
rare monster tropical cyclones (the term for hurricanes, typhoons and
other tropical storms) could inundate coastal areas with storm surges
greater than 15 feet (4.6 meters), and could even surpass 30 feet (9
m) in some regions of the world. The research was described here
yesterday (Dec. 3) at the annual meeting of the American Geophysical
Union.
By
simulating thousands of possible future storms, researchers
identified the outliers that could hit coastal areas in the future
but that wouldn't show up in predictions based solely on historical
records, said Ning Lin, a professor at Princeton University. The
scientists relied on the same model the National Weather Service uses
to predict hurricane activity for a given season.
Extreme
of extremes
Lin
and colleague Kerry Emanuel of MIT looked at the possible storm surge
from extreme storms in three locations: Tampa Bay, Fla., Dubai,
United Arab Emirates (UAE), and Darwin, Australia.
Lin
said more than 16 feet (5 m) of surge was possible in Tampa Bay. A
Florida black swan hurricane would move northward, parallel to the
west Florida coast. The probability of one of these storms hitting
Tampa Bay is one in 10,000, Lin said.
Even
though Hurricane Sandy broke several records and generated tremendous
storm surge, the superstorm was not a black swan, Lin said. The
simulated storm surges calculated by the model for New York, at up to
16 feet, top the record set by Hurricane Sandy, at 14 feet (4.3 m) —
part of which was the high tide at the time. [Infographic: Timeline
of Sandy's Week of Destruction]
Tropical
cyclones are already extremely rare in the Arabian Sea, with its low
humidity and high wind shear, which disrupts storm formation, but one
made landfall in Oman and Iran in 2007. Extreme storm surges of 30
feet (9 m) in Abu Dhabi, UAE, and Doha, Qatar, and 23 feet (7 m) in
Dubai are possible as a result of a black swan storm, the researchers
report in their abstract for the meeting.
Finally,
in Darwin, which was immensely devastated by Cyclone Tracy in 1974, a
black swan storm could generate surges above 33 feet (10 m), the
researchers plan to report in a talk on their findings on Tuesday.
Global
warming and extremes
The
model Lin and Emanuel used to look at the effect of black swans takes
into account the effects of climate change.
Rising
ocean temperatures have shifted the intensity of tropical cyclones,
which include hurricanes and typhoons, to higher levels. In the past
century, sea surface temperatures have risen 0.9 degree Fahrenheit
(0.5 degree Celsius) globally. Scientists continue to debate whether
this increase in temperature will boost the intensity or decrease the
number of storms. Globally, about 90 tropical cyclones, on average,
occur every year.
"There's
still a debate about the impact of climate change on tropical
cyclones," Lin said. "Most studies show that the intensity
of tropical cyclones tends to increase under the impact of climate
change. Some say that the frequency of total storms will decrease,"
she said.
However,
Lin added, "When we talk about black swans, we talk about the
extreme of the extremes. The total fraction [of extreme storms] will
increase even though the total numbers will decrease."
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