Less Dusty Air Warms Atlantic, May Spur Hurricanes
Date: 27-Mar-09
Country: NORWAY
Author: Alister Doyle, Environment Correspondent
Less Dusty Air Warms Atlantic, May Spur Hurricanes
decline in sun-dimming airborne dust has caused a fast
warming of the tropical North Atlantic in recent decades, according to a
study that might help predict hurricanes on the other side of the ocean.
Photo: REUTERS/NOAA/Handout
OSLO - A decline in sun-dimming airborne dust has caused a fast warming of
the tropical North Atlantic in recent decades, according to a study that
might help predict hurricanes on the other side of the ocean.
About 70 percent of the warming of the Atlantic since the early 1980s was
caused by less dust, blown from Saharan sandstorms or caused by volcanic
eruptions, U.S.-based scientists wrote in the journal Science.
Clouds of dust can be blown thousands of kilometers (miles) and reflect some
of the sun's rays back into space.
"Since 1980 tropical North Atlantic Ocean temperatures have been rising at a
rate of nearly 0.25 Celsius (0.45 F) per decade," they wrote on Thursday.
In the past, the rapid temperature rise had been blamed on factors such as
global warming or shifts in ocean currents. Warmer temperatures may spur
more hurricanes, which need sea surface temperatures of about 28 Celsius
(82.40F) to form.
A sea temperature difference of just one Fahrenheit separated 1994, a quiet
hurricane year, from a record 2005 when storms included Hurricane Katrina,
which devastated New Orleans, according to a University of Wisconsin-Madison
statement.
"We were surprised" by the big role of dust on Atlantic temperatures, said
Ralf Bennartz, a professor at the university and a co-author of the study
written with experts at the National Oceanic and Atmospheric Administration.
COOLER
In past decades "there was much more dust blowing from (Africa) onto the
Atlantic and cooling the sea and ... potentially suppressing hurricane
intensity," he told Reuters. No other ocean receives so much dust.
More droughts in Africa in the 1980s, for instance, meant more dust in the
air, he said of the study of satellite data and climate models. Annual
emissions of dust from North Africa have been estimated at between 240
million and 1.6 billion tonnes.
Bennartz said the scientists were trying to work out, for instance, if wet
weather in North Africa could mean less dust and in turn point to fewer
hurricanes battering the United States or Caribbean islands.
Big volcanic eruptions were El Chichon in Mexico in 1982 and Mount Pinatubo
in the Philippines in 1991. Both dimmed the sun.
The study suggests that only 30 percent of the warming of the Atlantic can
be explained by factors other than dust, for instance global warming blamed
by the U.N. Climate Panel on emissions of greenhouse gases from burning
fossil fuels.
"This makes sense, because we don't really expect global warming to make the
ocean (temperatures) increase that fast," said Amato Evan, a researcher at
the University of Wisconsin-Madison who was lead author.
Bennartz said it was unclear how climate change might affect overall dust
amounts blown from Africa this century.
(Editing by Janet Lawrence)
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