Number range CHAPTER© 2005 by Leo Poppoff

October 6, 2005

Basin Watch

by

Leo Poppoff

GLOBAL SPREAD OF POLLUTION

During springtime on the Mongolian Plateau, soils dry out. When frontal
systems with strong winds sweep across Mongolia, they pick up soil from
the surface, and create unbelievable dust storms. The sky turns reddish
and then black. Visibility is measured in tens of meters. Livestock get
lost and die.

Prevailing winds carry the dust over northern China and Korea. These
storms are know as Yellow Sand Events in Asia. And as they sweep across
Asian industrial centers, they pick up soot and sulfates and other
pollutants. The journey of this load of dust and pollutants continues
across the Pacific, sweeping across the northern coast of the United
States.

These Yellow Sand events have probably been going on for millennia. But,
more recent

land use changes might well have increased the severity of this natural
phenomenon.

Eric Wilcox, who has participated in several field research programs to
study dust and other pollutants from Asia, described aircraft flights
off Trinidad Head from which he could see plumes of dust blowing across
the Northern California coast. Wilcox is a NASA scientist at the Goddard
Space Center, studying how global pollution affects climate.

According to Wilcox, pollutants also originate in India, and are driven
by Monsoon systems. Those pollutants move south toward the equator, and
a fraction actually moves into the Southern Hemisphere. Still, a portion
of those pollutants, Wilcox explained, can be caught up by the winds
that blow west to east across the Pacific, joining pollutants from
Mongolia, China and Korea.

A large fraction of Asian aerosols (tiny particles floating in the air)
don't survive the trip. Larger dust particles simply fall to the ground
or into the ocean. Soluble particles, like sulfates, gather water to
form cloud droplets which might rain out. Soot and dust particles can
also nucleate cloud droplets, but not as easily. Dust and water droplets
can be detected because they reflect and scatter light.

NASA's Terra and Aqua satellites carry an instrument called MODIS. It's
a multichannel scanner that can detect and measure light in many optical
and near infrared bands. The light scattered from Asian aerosols are
recorded by the MODIS instrument and sent to NASA ground stations. The
data are converted into images of clouds moving across the Pacific
ocean. Analysis of satellite data also provides information about the
cloud's optical depth, which is a measure of the cloud's thickness.
According to Wilcox, optical depths are greater over the polluted skies
of industrial centers.

Scientists, studying satellite imagery can tell that pollution is
global. We get it from Asia. Southern states get it from the Sahara, and
Alaska gets it from eastern Europe. But, then we send our pollution
across the country and on to Europe, which in turn sends its pollutants
to Asia and Africa. We're all in it together.

Wilcox said that the Asian aerosol particles last about five to ten days
in the atmosphere, and that's little more than the time it takes to
cross the Pacific. So, pollution clouds that cross the continent and
over the Atlantic are mostly home grown.

But, there's another, very important, aspect to this global pollution.
The clouds of particles, soot, sulfates and water droplets reflect,
scatter and absorb sunlight. This affects the heat balance of the earth
by diminishing the amount of sunshine that reaches the surface, and,
thereby, reducing the heating.

"It's been well established," Wilcox said, "that the full magnitude of
greenhouse warming has not been realized because of the counteracting
cooling from clear sky aerosols. So, there's a climate cooling,
mitigating the greenhouse gas warming. We can estimate the global
radiative cooling effect of clear sky aerosols, and it's significant
compared to greenhouse gas warming. The best estimate is that it's a
fraction of the magnitude of greenhouse warming, but it's a significant
fraction -- something like 10 to 30 percent, I would guess."

Wilcox added that "an even bigger question mark is the interaction with
clouds. We believe that clouds are impacted by aerosols. And the
magnitude of that, globally, in terms of radiative impact, may be
significant as well, comparable or even greater than the impact of
aerosols in the clear sky. The idea here is that if you have a cloud
that incorporates a lot of aerosol it makes the cloud droplets smaller,
and that may make the clouds brighter, which will cool the planet."

Now, here's an environmental conundrum. We want to eliminate, or at
least greatly reduce, industrial pollution. But, if we were successful,
global warming would surely increase.

What's the connection of all this to Tahoe? As we noted in an earlier
column, these Asian aerosols could be affecting visibility in the Basin
and over the rest of the Sierra. Also, global warming will affect us as
well as the rest of the world. And last, but not least, Eric Wilcox's
dad, John Wilcox, is one of the founders, and currently President, of
the highly successful Squaw Valley Institute. And it was John's email
that led to this article.

Questions or comments? Send them to basinwatch@sbcglobal.net