[StBernard] Do We Need a Category 6?

[Westley Annis]

Do We Need a Category 6?
By BILL BLAKEMORE
 
(May 21) - There is no official Category 6 for hurricanes, but scientists
say they're pondering whether there should be as evidence mounts that
hurricanes around the world have sharply worsened over the past 30 years --
and all but a handful of hurricane experts now agree this worsening bears
the fingerprints of man-made global warming.

In fact, say scientists, there have already been hurricanes strong enough to
qualify as Category 6s. They'd define those as having sustained winds over
175 or 180 mph. A couple told me they'd measured close to 200 mph on a few
occasions.

The Saffir-Simpson hurricane category scale is based on wind speed: A
Category 1 hurricane has sustained winds from 74 to 95 mph, Category 2 has
sustained winds from 96 to 110 mph, Category 3 has sustained winds from 111
to 130 mph, Category 4 has sustained winds from 131 to 155, and a Category 5
storm has sustained winds greater than 155 mph.

The categories run in roughly 20 mph increments, so a Cat 6 would be greater
than 175 or 180 mph.

"Remember, for each 10 mph increase of wind speed," says atmosphere
scientist Greg Holland, "there's about 10 times more damage, and 20 times
more financial loss."

In other words, the increase is not "linear" but "exponential."

To put this all in perspective, Katrina was a Category 5 hurricane out over
some hot spots in the Gulf. But when it hit New Orleans, scientists now
know, Katrina had winds at a low Category 3, and much of them Category 2,
including the "left side winds" that then came down from the north and
pushed the surge-swollen waters of Lake Pontchartrain over and through
NOLA's levees. (Hurricanes spin counterclockwise in the northern hemisphere,
so when Katrina came ashore just east of New Orleans, its winds hit the city
from the north.)

Only three Category 5s have come ashore in the United States in the past
century -- the 1935 Labor Day Hurricane, Camille in 1969 and Andrew in 1992.

But because of man-made global warming, most hurricane scientists say now we
will probably be getting Category 4 and 5 hurricanes more frequently in the
coming decades.

That's on top of the natural multi-year cycles of hurricane intensity the
scientists already know about.

In fact, says Greg Holland, the world already has seen far more frequent Cat
4s and 5s. He points to several studies published over the past 12 months
which "indicated the frequency of Category 4 and 5 hurricanes had almost
doubled around the world in the period since 1970."

The fact that these patterns (on top of the natural cycles) have been seen
in not just one ocean but all tropical and subtropical waters around the
world is what worries many hurricane experts -- and, they say, it is why
they now calculate that they are due to man-made global warming, not
regional natural weather patterns.

"We're actually looking at an entire world that is heating up," says
Holland, "not just the Atlantic Ocean -- which is why we are absolutely
convinced that there is a very large greenhouse warming signal in what we're
seeing."

In the past, say these scientists, when one region of the globe concentrated
more heated water or air (both of which can intensify hurricanes), other
regions would cool in compensation because the total heat available on the
planet at any one time is limited; now, with the average global temperatures
going up, such related cooling is happening less and less.

Greg Holland's research base -- the National Center for Atmospheric Research
in Boulder, Colo. -- receives overwhelming evidence for the human
contribution to global warming constantly now, challenging NCAR's ranks of
world class climatologists (and their sleek black humming supercomputers in
the basement) to produce ever more refined predictions of the planet's
rising fever over the next few decades.

How well did the National Oceanic and Atmospheric Administration do a year
ago in predicting the 2005 Atlantic hurricane season? Not so well, and the
relatively new and unfamiliar factors of manmade global warming, say some
scientists, may be part of what threw last year's predictions off.

In May 2005, NOAA predicted the summer Atlantic would see 12 to 15 named
tropical storms. There were 28. It predicted seven to nine storms would
become hurricanes, with winds of at least 74 mph. Fifteen did. It predicted
three to five of the hurricanes would be "major," with winds of at least 111
mph. Seven were, and six of them came ashore in the United States.

A "Category 6?"

Making that official, say several hurricane scientists, would require sober
deliberation by their guild, assessing whether there would be any real
advantage to it -- even though it seems reasonable to expect that the
frequency of storms we have already seen with sustained winds over 175 or
180 mph may indeed creep up as the globe keeps warming.

Category 5, they point out, is already bad enough, way beyond almost
everyone's ability to imagine, given that Katrina came ashore as a 3.