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BLACK CARBON
CONTRIBUTES TO DROUGHTS AND FLOODS IN CHINA - Click here for images/maps
of region
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1 | | | A
new NASA climate study has found that large amounts of black carbon (soot) particles
and other pollutants are causing changes in precipitation and temperatures over
China and may be at least partially responsible for the tendency toward increased
floods and droughts in those regions over the last several decades. In
a paper appearing in the September 27 issue of SCIENCE, Surabi Menon of NASA and
Columbia University, and her colleague, James Hansen of NASA's Goddard Institute
for Space Studies, New York, indicate that black carbon can affect regional climate
by absorbing sunlight, heating the air and thereby altering large scale atmospheric
circulation and the hydrologic cycle.
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2 | | | Using
the NASA Goddard Institute for Space Studies climate computer model, and aerosol
data from 46 ground stations in China, Menon and Hansen conducted four sets of
computer simulations to monitor the effects of black carbon on the hydrologic
cycle over China and India. The aerosol data from the Chinese ground stations
were provided by Yunfeng Luo, a co-author on the study from the Institute of Atmospheric
Physics, Chinese Academy of Sciences. In
the four numerical simulations, Menon and Hansen isolated specific factors such
as sea surface temperature, other greenhouse gases, and aerosols and analyzed
whether changes in those factors would be responsible for hydrologic cycle changes.
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3 and 4 | |
Click
on top image for a movie of the region over time showing the flooding. |
Out
of the four scenarios, the effect of increased amounts of soot (over southern
China) created a clear tendency toward the flooding scenario that has been occurring
in southern China and the increasing drought over northern China that has persisted
over the last several years.
"If
our interpretation is correct, then reducing the amount of black carbon or soot
may help diminish the intensity of floods in the south and droughts in the northern
areas of China, in addition to having human health benefits," Hansen said.
Currently research is being conducted to verify a similar pattern over India.
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5 | | Click
on image for the animation. | Black
carbon or soot is generated from industrial pollution, traffic, outdoor fires,
and household burning of coal and biomass fuels. Soot is a product of incomplete
combustion especially of coal, diesel fuels, biofuels and outdoor biomass burning.
Emissions are large in China and India because cooking and heating are done with
wood, field residue, cow dung, and coal, at a low temperature that does not allow
for complete combustion. These resulting soot particles absorb sunlight, just
as dark pavement becomes hotter than light pavement in the summertime. When
soot absorbs sunlight it heats the air and reduces the amount of sunlight reaching
the ground. The heated air makes the atmosphere more unstable, creating rising
air (convection) which forms clouds and brings rainfall to regions that are heavily
polluted. (See Image 5)
The
increase of rising air in southern China is balanced by an increase of sinking
air (subsidence) and drying in northern China. When air sinks, clouds and thus,
rain, cannot form, creating dry conditions. For example, deserts are places where
subsidence occurs. In
recent years, northern China has suffered from an increased severity of dust storms,
while southern China has had increased rainfall that is thought to be the largest
change in precipitation trends since the year 950. Menon and Hansen believe that
human-made sunlight-absorbing aerosols may be responsible. This
research continues long-term observations of global climate change and was funded
by NASA's Earth Science Enterprise and the National Science Foundation. NASA's
Earth Science Enterprise is dedicated to helping us to better understand and protect
our home planet.
SOOT
CHANGES GROUND TEMPERATURES IN ASIA Soot
blocks the Sun's energy from reaching the ground and cools the surface. This image,
derived from the GISS climate computer model, and aerosol data from 46 ground
stations in China, shows black carbon's effect in lowering surface temperatures
during the summer months (June, July and August). Cooler temperatures are denoted
by the blue colorations. This map shows cooling of 0.5 to 1.0 degrees Celsius
(.9-1.8 degrees Fahrenheit) occurring over China, and warming temperatures throughout
the rest of the world (in yellow). As soot heats the lower atmosphere over China
some of this warm air can get transported to the other regions of the world and
can cause surface warming in distant locations.
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6 | | Click
on Asia to see a close up of the region. Click on North/South America to enlarge
this image. |
SOOT
INTENSIFIES FLOODING AND DROUGHTS IN ASIA Soot
intensifies rainfall in polluted regions. The black carbon aerosols soak up the
Sun's rays heating up the atmosphere. Air rises and creates rain clouds over polluted
areas. Rising air is balanced by an increase in sinking air and drying in neighboring
regions. When air sinks, clouds and thus, rain, cannot form, creating dry conditions. This
image, derived from the GISS climate computer model, and aerosol data from 46
ground stations in China, shows how black carbon can change rainfall patterns
over the northern and southern regions of China during the summer months of June,
July and August. The blue colors indicate regions in which the simulations yield
a tendency for increased rainfall by as much as 10 inches over the summer. Other
regions (brown colors) have decreased rainfall by as much as several inches or
more. Ground station aerosol data was provided by co-author Dr. Y. Luo of the
National Science Foundation of China, Haidian, China..
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| Image
7 | | Click
on Asia to see a close up of the region. Click on North/South America to enlarge
this image. |
SUNBLOCK
REDUCES CROP YIELDS Soot
can block the Sun's energy from the ground and reduce crop yields. This image,
derived from the NASA Goddard Institute for Space Studies (GISS) climate computer
model, and aerosol data from 46 ground stations in China, shows the decrease in
solar energy reaching the ground (in black) during the summer months (June, July
and August). Yellow shows were the sunlight has increased.
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| Image
8 | | Click
on Asia to see a close up of the region. Click on North/South America to enlarge
this image. |
PUTTING
IT ALL TOGETHER This
animation takes a closer look at Asia and cycles through the maps showing how
black carbon can change ground temperatures, rainfall and sunlight over China
and India.
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| Image
9 | | Click
on image to see an animation of all three maps and how they relate. |
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