Colorado State University Emeritus
Professor William Gray says it’s Mother Nature, not humans, that will cause an
active hurricane season this year.
Noted for his yearly Atlantic Basin
hurricane season forecasts, on which he is now co-author along with colleague
Phil Klotzbach, Gray has long dismissed the theory that global warming has
caused an increase in hurricane activity or intensity.
At the National Hurricane
Conference on 31 March, Gray spoke about the effects of increased carbon
dioxide in the atmosphere – the supposed catalyst of global warming – on
Klotzbach and Gray said the
Atlantic Basin has been in active hurricane period since 1995 because of
something called thermohaline circulation in the Atlantic Ocean.
“It’s been active since then and
there is no reason we should think the next years are going to be much
different,” he said. “Some people say it’s humans that are causing this. I say
“We have to worry about nature, not
Discussing the matter in an
interview, Gray said that the theory is that carbon dioxide traps infrared
radiation in the atmosphere, which in turn warms the sea surface temperature
and creates a greater lapse rate, or temperature variation, between the ocean
surface and the upper atmosphere.
Greater lapse rates create more intense thunderstorm clouds, which give
rise to more tropical cyclones.
“In a climate sense if the globe
warms a bit the [sea surface temperatures] warm, the upper levels are going to
warm some, and the lapse rates aren’t going to change that much,” he said. “The
people who have been saying [more CO2 in the atmosphere causes more hurricanes]
don’t know how hurricanes work, basically.”
Klotzbach agreed with his colleague
that warmer sea surface temperatures alone aren’t the cause of more hurricanes.
“When you talk about a global
warming perspective, you’re not just warming the surface you’re warming the
upper level as well,” he said. “So when you warm both… you’re not really
going to make the atmosphere that much more unstable.”
Klotzbach said global warming could
actually cause fewer storms in the Atlantic Basin if it warmed the tropical
Pacific Ocean enough that an El Niño pattern became the norm. El Niño, which is caused by a warming of the
sea surface temperatures in the tropical eastern Pacific Ocean, creates
stronger wind shear in the Atlantic, which is known to inhibit the formation
and strengthening of tropical cyclones.
“You could see more storms in the
Pacific and fewer storms in the Atlantic,” Klotzbach said.
The two think this year’s hurricane
season is going to be very active for a number of reasons, starting with the
phase of the thermohaline circulation in the Atlantic. This circulation involves natural fluctuations in the salt content of
the ocean, which affects sea surface temperatures. But Gray said even higher sea surface
temperatures alone won’t cause more hurricanes.
“It’s not the sea surface temperatures
that do it,” he said. “It’s what [higher sea surface temperatures] mean for
other things If you have higher SSTs, you typically have the trade winds a
little weaker, the vertical sheers a little less, the pressures a little lower.
“The SSTs are a good proxy, but for
themselves they don’t play [the only role in hurricane formation]. If you keep everything else the same and just
change the sea surface temperatures, it’s not going to make that much difference.”
El Niño is predicted to dissipate
this summer and that, in combination, with the higher sea surface temperatures
and other atmospheric conditions, is expected to lead to the active season.
Gray and Klotzbach are quick to point out that the current active phase of
thermohaline circulation is not creating more intense hurricane seasons than it
last 15-year active period of 1995-2009 has not been more active than the
earlier 15-year period of 1950-1964, when the Atlantic Ocean circulation
conditions were similar to what has been observed in the last 15 years.
conditions occurred even though atmospheric CO2 amounts were much lower in the
two talked about the increase of tropical cyclone activity, especially major
hurricanes, around the Cayman Islands area since 2004.
said it was the deep, warm waters in the Western Caribbean that allow storms to
intensify in general, but it’s partially been bad luck that so many major
hurricanes have come near the Cayman Islands recently.
said six major hurricanes come within 100 miles of the Cayman Islands in the
six hurricane seasons since 2004. Prior to that, only six major hurricanes came
within 100 miles of the Cayman Islands in the 87 years between 1917 and 2003.
also said that there is no evidence that the hurricane seasons are more active
now than in years past, partially because satellite technology did not exist
before the 1960s and many cyclones went unreported. In addition, Klotzbach said during the
record-breaking 2005 hurricane season, when there were 28 names storms, eight
entered the Caribbean. However, in 1933,
during another active thermohaline period, there were 15 named storms in the
Caribbean, he said.
year’s quiet hurricane season for Cayman was caused by El
Niño, Klotzbach said.
“The El Niño impact in the
Caribbean is very, very large, much bigger than the rest of the Atlantic,” he
said, adding that he has written a paper on the subject of El Niño and the Caribbean that he hopes will
be published this year.