New Evidence That Global Warming Fuels Stronger Atlantic Hurricanes
Pastor Dale Morgan
New Evidence That Global Warming Fuels Stronger Atlantic Hurricanes*
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Big Storms More Important Than Thought*
New York (UPI) Mar 01 - U.S. researchers have determined typhoons and
hurricanes are the dominant cause of mixing between the Earth's
troposphere and stratosphere. Deep air convection influences climate
through injecting water-vapor-rich, ozone-poor air from Earth's near
surface to the upper troposphere and lower stratosphere and displacing
water-vapor-poor, ozone-rich air downward. However, scientists say the
mechanisms driving that convection are poorly understood, especially in
the tropics, where, instead of being marked by a sharp transition in
temperature, the boundary between the troposphere and the stratosphere
is a diffuse region of nearly constant temperature.
William Rossow of the City University of New York and Cindy Pearl of the
Goddard Institute for Space Studies at Columbia University, conducted a
22-year survey of tropical convection. They found deep convection occurs
mostly in larger, more organized convective systems, with smaller,
unorganized convective systems rarely penetrating the stratosphere.
Durations of penetration are longest for the larger systems, such as
hurricanes and typhoons, which generally exceed one day. The authors
suggest the role of such tropical storms should be examined more
closely, since, although intermittent, they dominate
stratosphere-troposphere exchanges. The study appears in the journal
Geophysical Research Letters.
by Staff Writers
Madison WI (SPX) Mar 01, 2007
Atmospheric scientists have uncovered fresh evidence to support the
hotly debated theory that global warming has contributed to the
emergence of stronger hurricanes in the Atlantic Ocean. The unsettling
trend is confined to the Atlantic, however, and does not hold up in any
of the world's other oceans, researchers have also found.
Scientists at the University of Wisconsin-Madison and the National
Climatic Data Center (NCDC) of the National Oceanic and Atmospheric
Administration reported the finding in the journal Geophysical Research
Letters. The work should help resolve some of the controversy that has
swirled around two prominent studies that drew connections last year
between global warming and the onset of increasingly intense hurricanes.
"The debate is not about scientific methods, but instead centers around
the quality of hurricane data," says lead author James Kossin, a
research scientist at UW-Madison's Cooperative Institute for
Meteorological Satellite Studies. "So we thought, 'Lets take the first
step toward resolving this debate.'"
The inconsistent nature of hurricane data has been a sore spot within
the hurricane research community for decades. Before the advent of
weather satellites, scientists were forced to rely on scattered ship
reports and sailor logs to stay abreast of storm conditions. The advent
of weather satellites during the 1960s dramatically improved the
situation, but the technology has changed so rapidly that newer
satellite records are barely consistent with older ones.
Kossin and his colleagues realized they needed to smooth out the data
before exploring any interplay between warmer temperatures and hurricane
activity. Working with an existing NCDC archive that holds global
satellite information for the years 1983 through 2005, the researchers
evened out the numbers by essentially simplifying newer satellite
information to align it with older records.
"This new dataset is unlike anything that's been done before," says
Kossin. "It's going to serve a purpose as being the only globally
consistent dataset around. The caveat of course, is that it only goes
back to 1983."
Even so, it's a good start. Once the NCDC researchers recalibrated the
hurricane figures, Kossin took a fresh look at how the new numbers on
hurricane strength correlate with records on warming ocean temperatures,
a side effect of global warming.
What he found both supported and contradicted previous findings. "The
data says that the Atlantic has been trending upwards in hurricane
intensity quite a bit," says Kossin. "But the trends appear to be
inflated or spurious everywhere else, meaning that we still can't make
any global statements."
Sea-surface temperatures may be one reason why greenhouse gases are
exacting a unique toll on the Atlantic Ocean, says Kossin. Hurricanes
need temperatures of around 27 degrees Celsius (81 degrees Fahrenheit)
to gather steam. On average, the Atlantic's surface is slightly colder
than that but other oceans, such as the Western Pacific, are naturally
much warmer.
"The average conditions in the Atlantic at any given time are just on
the cusp of what it takes for a hurricane to form," says Kossin. " So it
might be that imposing only a small (man-made) change in conditions,
creates a much better chance of having a hurricane."
The Atlantic is also unique in that all the physical variables that
converge to form hurricanes - including wind speeds, wind directions and
temperatures - mysteriously feed off each other in ways that only make
conditions more ripe for a storm. But scientists don't really understand
why, Kossin adds.
"While we can see a correlation between global warming and hurricane
strength, we still need to understand exactly why the Atlantic is
reacting to warmer temperatures in this way, and that is much more
difficult to do," says Kossin. "We need to be creating models and
simulations to understand what is really happening here. From here on,
that is what we should be thinking about."
Co-authors Daniel Vimont, a UW-Madison atmospheric scientist, Ken Knapp,
a scientist at the NCDC, and Richard Murnane, a scientist at the Bermuda
Institute of Ocean Sciences, also contributed to the study.