China’s coal
consumption
in 1980
679
million tons
China’s coal
consumption
in 2002
1,413
million tons
China’s coal
consumption
in 2007
2,893
million tons
Sulfur stalled surface temperature
By Nadia Drake
A new study demonstrates why global
surface temperatures defied a decades-long trend and didn’t continue to rise
between 1998 and 2008: Pollution-spew-ing, coal-burning power plants in Asia,
while emitting warming greenhouse
gases, simultaneously sent cooling
sulfur particles into the atmosphere.
During that decade when
temps held steady — sometimes cited as evidence
against global warming—
these Asian emissions mostly
balanced one another and
dampened the natural cooling effects expected from
cycles of the sun and ocean.
A team of scientists led by
Boston University’s Robert
Kaufmann analyzed factors contributing
to global surface temperature, including
human-caused emissions, the 11-year
solar cycle and a shift from warming
El Niño to cooling La Niña climate patterns. Without human input, average
temperatures would have cooled, based
on the La Niña shift and decreasing solar
radiation, the researchers report online
July 5 in the Proceedings of the National
Academy of Sciences.
After simulating temperature changes
expected over the decade based on these
factors, the researchers identified the
smoking gun behind steady temperatures: sulfur particles belched into the
atmosphere by coal-burning power
plants. Sulfur aerosols reflect light back
into space and counteract the warming
effects of greenhouse gases.
“This looks like a very solid, careful
statistical analysis of the factors influencing recent global temperature changes,”
says climate scientist Michael E. Mann of
Pennsylvania State University, who was
not involved in the study.
Most of the increase in sulfur emissions came from China, where coal consumption more than doubled between
2002 and 2007, accounting for 77 percent of the rise in coal use worldwide,
the scientists report. During that period,
Kaufmann says, global sulfur emissions
increased by 26 percent. From 1998 to
2008, greenhouse gas and sulfur emissions effectively canceled each other out.
“Humans do two things to
the planet,” Kaufmann says.
“They warm it by emitting
greenhouse gases like car-
bon dioxide and methane,
and they cool it by emitting
these sulfur aerosols.”
Sending sulfur into the air
isn’t entirely helpful, though.
In addition to causing respiratory problems, sulfur
aerosols combine with water vapor to
form acid rain. “You wouldn’t want to
increase the amount of junk in the air to
decrease the effects of global warming,”
cautions climate scientist Gavin Schmidt
of NASA’s Goddard Institute for Space
Studies in New York City.
China has begun using scrubbers at its
coal-burning facilities to reduce sulfur
emissions, efforts similar to those in the
United States after passage of the Clean
Air Act in 1970. When sulfur emissions
are reduced, “what you will see in the
short term is a relative rapid rise in temperature, because you have taken away
the brake,” says Caspar Ammann, a climate scientist at the National Center for
Atmospheric Research in Boulder, Colo.
Judith Curry of Georgia Tech in
Atlanta notes that decadal oscillations
in ocean currents could also explain the
observed stall in temperature rise. But
Kaufmann argues that when sulfur is
removed from the analysis, the model
falls apart. “Only sulfur aerosols can
explain the recent pattern,” he says.
“You wouldn’t
want to
increase the
amount of
junk in the air
to decrease ...
warming.”
GAVIN SCHMIDT
Planes punch sky holes
airplane takeoffs and landings may
be affecting the weather around
them. when a plane flies through a
cloud containing supercooled water,
which is liquid despite being below
its freezing point, the plane triggers
the formation of ice crystals that
fall out as snow or rain. such super-
cooled clouds might exist around
airports up to 6 percent of the time,
scientists led by andrew Heymsfield
of the national Center for atmo-
spheric research in Boulder, Colo.,
report in the July 1 Science.
— Alexandra Witze
Glacier having a meltdown
ocean currents are scouring
antarctica’s floating Pine island
Glacier from below, causing it to
melt ever faster. american and
British scientists measured the
temperature and saltiness of water
around the glacier and found that
since 1994 the amount of meltwater from the ice has increased
by 50 percent. Pine island is
the fastest-shrinking glacier in
antarctica. the team reports the
findings online June 26 in Nature
Geoscience. — Alexandra Witze
Plastics link to diabetes
women exposed to relatively high
amounts of phthalates, used in
plastics and as solvents, are more
likely to be diabetic, a study in
mexico finds. although previous
studies have linked phthalates
with risk of obesity—itself a risk
factor for diabetes—the newly
identified association appears to
be independent of obesity, the
researchers report online June
21 in Environmental Research.
— Janet Raloff
www.sciencenews.org
July 30, 2011 | SCIENCE NEWS | 17
