A
controversial theory proposes mimicking volcanoes to fight global
warming. But throwing sulfur particles into the sky may do more harm
than good, a new study says.
The temporary solution would pump
particles of sulfur high into the atmosphere—simulating the effect of a
massive volcano by blocking out some of the sun's rays. This
intervention, advocates argue, would buy a little time to reduce
greenhouse gas emissions.
But as well as cooling the planet,
the sulfur particles would reduce rainfall and cause serious global
drought, a new study says.
"It is a Band-Aid fix that does not
work," said study co-author Kevin Trenberth of the National Center for
Atmospheric Research (NCAR) in Boulder, Colorado.
It's just one
of several drastic measures proposed to combat global warming, now that
most scientists are in agreement that carbon dioxide, primarily from
burning fossil fuels, is changing Earth's climate.
Drying Effects
Trenberth
and NCAR colleague Aiguo Dai studied worldwide rainfall and streamflow
records for the world's largest rivers between 1950 and 2004.
During
this period three major volcanic eruptions occurred: Mount Agung in
Indonesia in 1963, El Chichón in Mexico in 1982, and Mount Pinatubo in
the Philippines in 1991.
It's well known that particles thrown
into the atmosphere by volcanic eruptions cause a global cooling effect
by reflecting back sunlight.
In the case of Mount Pinatubo,
global temperatures dropped by an average of 0.9 degrees Fahrenheit
(0.5 degrees Celsius) the following year. But until now, no one had
been able to pin down the effect that these volcanoes might have had on
rainfall.
By carrying out statistical analysis on rainfall and
streamflow records, the researchers were able to detect a significant
drying effect after Mount Pinatubo's eruption.
There was less
rainfall over land, and a record decrease in runoff and ocean discharge
into the ocean from October 1991 to September 1992, the scientists
report this week in the journal Geophysical Research Letters.
The
researchers found that Mount Pinatubo's eruption still kept much of the
world dry, even after taking into consideration the drying effects of
El Niño—an abnormal warming of surface ocean waters in the eastern
tropical Pacific.
Reduced Rainfall
It's not clear why the sulfur particles reduce rainfall, but the team has a theory.
"First the particles block out the sun and cool off the land, making the rain move over the oceans," Trenberth said.
"Then they cool off the oceans—and that reduces evaporation and thus global precipitation."
In
the case of the Agung and El Chichón eruptions, there was no detectable
reduction in global precipitation. That's probably because these
volcanoes didn't have quite as much oomph as Mount Pinatubo, experts
say.
(Related: "Volcanic Activity Triggered Deadly Prehistoric Warming" [April 26, 2007].)
Solar Shield?
The
findings should ring alarm bells for those considering pumping sulfur
into the skies—and creating a solar shield—as a solution to global
warming, the researchers warned. (Get the basics on global warming.)
"Our
results suggest that major adverse effects, including drought, could
arise from such 'geoengineering' solutions," Trenberth said.
Not everyone agrees that these findings rule out a solar shield.
"While
looking at volcanoes as an analog for geoengineering is a good
approach, we should be careful not to overinterpret the analogy," said
Ken Caldeira, a geoscientist with the Carnegie Institution of
Washington.
Caldeira has modeled the effect that a sulfur solar shield would have.
Volcanic
eruptions throw tons of particles into the atmosphere in just a few
days. But planned schemes would inject particles slowly over decades.
Caldeira said such differences make it difficult to compare planned schemes with volcanoes.
Kate Ravilious
© National Geographic News
Wednesday, 22 August 2007 22:37
"Volcano Cure" for Warming? Not So Fast, Study Says
Written by News Desk
A
controversial theory proposes mimicking volcanoes to fight global
warming. But throwing sulfur particles into the sky may do more harm
than good, a new study says.
Published in
Climate Change
