[cdn-nucl-l] How Does Anthropogenic Haze Influence Climate?

["Adam McLean" <adam.mclean@utoronto.ca>]

Posted on the Nasa Earth Observatory web page on May 27, 2003 and at:
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=15295
The truly global influence of smog.

For those in Southern Ontario that wonder what the atmosphere looks like
from orbit on a 'smog alert' day, check out:
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4490

Adam

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How Does Anthropogenic Haze Influence Climate?  Click here to view full
image (1093 kb)  
 
Greenhouse gases act broadly to warm the atmosphere, but human-induced
aerosols (particles in the atmosphere) generate negative forcings—that is
cooling of the atmosphere by reflection of the sun’s energy away from Earth.
The above photograph from the Space Shuttle was featured in an article in
Science magazine this week (Science vol. 300: 1103-1104). It shows haze from
China spread over the Pacific Ocean, on March 4, 1996.

In the Science article, Anderson and coworkers point out that greenhouse gas
forcing on climate is fairly well understood, but the effect of aerosols is
not. Two ways of estimating the “forcing,” or push, on global climate caused
by aerosols give inconsistent results. So-called “inverse” calculations
constrain such cooling to a range of –1.0 to –1.9 Watts per square meter,
whereas “forward” calculations suggest far greater negative forcing, as much
as –3 W/m2 or more. Photographs taken by astronauts illustrate the kind of
reflective smog plumes that cause surface cooling.

The photograph shows a coherent corridor of anthropogenic haze (arrows),
probably a mixture of industrial air pollution, dust, and smoke, in the left
half of the view against the dark background of the East China Sea
(Wilkinson et al. 2000). The corridor is ~200 km wide and probably much more
than 600 km long (the visible length over the sea). In this
southwest-looking view, the island of Taiwan appears top left and the east
coast of China across the rest of the view. The picture was taken as the
Space Shuttle flew over Okinawa. Shanghai lies at the near point on the
Chinese coastline (top right)—about 650 km away. The transport of smog from
East Asia has been confirmed in measurements of the atmosphere over North
America.

The uncertainty in understanding aerosol forcing of global temperature means
that its effect in counteracting greenhouse-gas warming is still largely
unknown. The Science article concludes that the 0.6 Kelvin rise in average
global surface temperature in the last 130 years may be due to natural
variability in the atmosphere that could be far higher than currently
understood; and/or to much higher sensitivity in the climate system. The
article nevertheless concludes that by the middle of this century the
absolute accumulation of greenhouse gases, compared to the non-accumulation
of aerosols, “will inevitably result in a strong, positive forcing of
Earth’s climate system”.

References 
Anderson, T. L., R. J. Charlson, S. E. Schwartz, R. Knutti, O. Boucher, H.
Rodhe, and J. Heitzenberg, 2003, Climate forcing by aerosols—a hazy picture,
Science (16 May 2003) 300: 1103-1104.

M. J. Wilkinson, M. J., J. D. Wheeler, R. J. Charlson, and K. P. Lulla,
2000, Imaging Aerosols from Low Earth Orbit: Photographic Results From the
Shuttle-Mir and Shuttle Programs, in K. P. Lulla and L. V. Dessinov (ed.)
Dynamic Earth Environments, New York: Wiley. Ch. 6.

NASA photographSTS075-773-66, was taken March 4, 1996, 01:29:47 GMT, center
point 28°N 123°E, craft nadir 28°N 128.1°W, from an altitude of 278 km, with
a Hasselblad film camera and 40 mm lens. The image was provided by the Earth
Sciences and Image Analysis Laboratory at Johnson Space Center. Additional
images taken by astronauts and cosmonauts can be viewed at the NASA-JSC
Gateway to Astronaut Photography of Earth.