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发帖数: 19049 | 1 An international team of scientists says it's figured out how to slow global
warming in the short run and prevent millions of deaths from dirty air:
Stop focusing so much on carbon dioxide.
They say the key is to reduce emissions of two powerful and fast-acting
causes of global warming — methane and soot.
Carbon dioxide is the chief greenhouse gas and the one world leaders have
spent the most time talking about controlling. Scientists say carbon dioxide
from fossil fuels like coal and oil is a bigger overall cause of global
warming, but reducing methane and soot offers quicker fixes.
Soot also is a big health problem, so dramatically cutting it with existing
technology would save between 700,000 and 4.7 million lives each year,
according to the team's research published online Thursday in the journal
Science. Since soot causes rainfall patterns to shift, reducing it would cut
down on droughts in southern Europe and parts of Africa and ease monsoon
problems in Asia, the study says.
Two dozen scientists from around the world ran computer models of 400
different existing pollution control measures and came up with 14 methods
that attack methane and soot. The idea has been around for more than a
decade and the same authors worked on a United Nations report last year, but
this new study is far more comprehensive.
All 14 methods — capturing methane from landfills and coal mines, cleaning
up cook stoves and diesel engines, and changing agriculture techniques for
rice paddies and manure collection — are being used efficiently in many
places, but aren't universally adopted, said the study's lead author, Drew
Shindell of NASA.
If adopted more widely, the scientists calculate that would reduce projected
global warming by 0.9 degrees Fahrenheit (0.5 degrees Celsius) by the year
2050. Without the measures, global average temperature is projected to rise
nearly 2.2 degrees Fahrenheit (1.2 degrees Celsius) in the next four decades
. But controlling methane and soot, the increase is projected to be only 1.3
degrees (0.7 degrees Celsius). It also would increase annual yield of key
crops worldwide by almost 150 million tons (135 million metric tons).
Methane comes from landfills, farms, drilling for natural gas, and coal
mining. Soot, called black carbon by scientists, is a byproduct of burning
and is a big problem with cook stoves using wood, dung and coal in
developing countries and in some diesel fuels worldwide.
Reducing methane and black carbon isn't the very best way to attack climate
change, air pollution, or hunger, but reducing those chemicals are among the
better ways and work simultaneously on all three problems, Shindell said.
And shifting the pollution focus doesn't mean ignoring carbon dioxide.
Shindell said: "The science says you really have to start on carbon dioxide
even now to get the benefit in the distant future."
It all comes down to basic chemistry. There's far more carbon dioxide
pollution than methane and soot pollution, but the last two are way more
potent. Carbon dioxide also lasts in the atmosphere longer.
A 2007 Stanford University study calculated that carbon dioxide was the No.
1 cause of man-made global warming, accounting for 48 percent of the problem
. Soot was second with 16 percent of the warming and methane was right
behind at 14 percent.
But over a 20-year period, a molecule of methane or soot causes
substantially more warming then a carbon dioxide molecule.
The new research won wide praise from outside scientists, including a
conservative researcher who held a top post in the George W. Bush
administration.
"So rather than focusing only on carbon dioxide emissions, where we have to
make a tradeoff with energy prices, this strategy focuses on 'win-win-win'
pathways that have benefits to human health, agriculture and stabilizing the
Earth's climate," said University of Minnesota ecology professor Jonathan
Foley, who wasn't part of the study. "That's brilliant."
John D. Graham, who oversaw regulations at the Office of Management and
Budget in the Bush administration and is now dean of public and
environmental affairs at Indiana University, said: "This is an important
study that deserves serious consideration by policy makers as well as
scientists."
The study even does a cost-benefit analysis to see if these pollution
control methods are too expensive to be anything but fantasy. They actually
pay off with benefits that are as much as ten times the value of the costs,
Shindell said. The paper calculates that as of 2030, the pollution reduction
methods would bring about $6.5 trillion in annual benefits from fewer
people dying from air pollution, less global warming and increased crop
production.
In the United States, Shindell calculates the measures would prevent about
14,000 air pollution deaths in people older than 30 by the year 2030. About
0.8 degrees Fahrenheit of projected warming in the U.S. would be prevented
by 2050.
But health benefits would be far bigger in China and India where soot is
more of a problem.
The study comes a day after the U.S. Environmental Protection Agency
released the most detailed data yet on American greenhouse gas emissions. Of
the emissions reported to the government, nearly three-quarters came from
power plants. But with methane, it's different. Nineteen of the top 20
methane emitters were landfills.
Stanford University climate scientist Chris Field, who is a leader in the
Intergovernmental Panel on Climate Change but wasn't part of this study,
praised the study but said he worried that officials would delay cutting
back on the more prevalent carbon dioxide. Focusing solely on methane and
soot and ignoring carbon dioxide "tends to exacerbate climate change," he
said.
Another outside climate expert Andrew Weaver of the University of Victoria
in Canada said the study is good news amid a sea of gloomy reports about
climate change.
"This is a no-brainer," he said. "We have solutions at hand." |
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