Here is a summary of a plenary talk at this summer's AAPT meeting. I tape-
recorded the talk and then took notes from the tape. I thought this talk
was one of the most interesting of the meeting!
Cheers,
Jane Jackson
Summary of the plenary talk: EARTH ON FIRE. (AAPT Summer Meeting, Aug. 1996)
Joel Levine, a scientist at NASA Langley Research Center and an
adjunct professor of physics at the College of William and Mary, spoke
about his NASA group's 6 years of research which concludes that man-made
fires, mostly in Africa, Brazil, and Siberia, are major contributors to
global warming. In 1992 his group collaborated with an organization of 12
nations which put 300 scientists to work for half a year taking data in
Africa and Brazil; their research suggests that fires are causing up to 1/3
of the excess carbon dioxide and excess ozone in the lower atmosphere
(where ozone is a pollutant).
Joel mentioned three implications of global warming.
* Rise in sea level, with flooding of land presently occupied by
hundreds of millions of people.
* Colder stratosphere, which will destroy more of the protective
ozone there, due to the reduced temperature.
* Havoc with day-to-day weather (more hurricanes, typhoons,
temperature extremes, etc.)
Background: carbon dioxide is the major contributor to global
warming; it's responsible for over half of the greenhouse effect associated
with global warming. Carbon dioxide is the major combustion product when
fossil fuels are burned. The level of carbon dioxide continues to rise
steadily, even though world use of fossil fuels leveled off in the 1980's
(due to fuel-efficient cars and increasing use of nuclear energy).
Puzzled by this, in 1988 scientists all over the world started
looking for other sources of carbon dioxide. In that year Joel's group were
given 40,000 spy satellite pictures of the Earth at night; the pictures
were taken every 10 days. They studied them and found that a vast amount of
man-made burning is occurring, particularly in Africa, Brazil and Siberia.
They were shocked to find that about 1% of the Earth's surface area burns
each year (100 times more than was previously thought).
When trees and other plants are burned, their carbon, which
constitutes almost half their weight, combines with oxygen to form carbon
dioxide. But 100 other gases are produced and released, too, several of
which are also bad for our atmosphere. One is methyl bromide, which is 40
times worse than chlorine for destroying stratospheric ozone: 1 of these
molecules which breaks in the stratosphere can destroy 2 million ozone
molecules! Also, almost 40% of the excess ozone in the lower atmosphere is
probably due to fires.
Consider the 3 major sources of global burning:
1) In Africa, tens of thousands of savanna fires are visible on
satellite photos each night. Africa has 10 million square kilometers of
savannas (grasslands). Joel spent 2 years in Africa doing research. Each
10-acre plot is burned 2 or 3 times each year! Although some carbon
dioxide is reabsorbed when the savanna grass grows again, the net effect is
still very bad.
2) Brazil is a major area of burning, as we all know. The world's
tropical forests are being burned at the rate of 50 acres per minute. 30%
of the world's tropical forests have been destroyed by burning, primarily
in the last 30 years.
3) Boreal forests constitute 30% of the forests on our planet; they
cover northern parts of the globe, and 2/3 are in Siberia. In Siberia the
boreal forests are being burned down for urban development.
So the fires on the planet, which occur in largest scale in
Brazil, Afica and Siberia, are having a large impact on the composition of
the atmosphere, and thereby are contributing significantly to global
warming.
During the question period Joel was asked what is known about how
carbon dioxide can be removed from the atmosphere. He said that scientists
have huge questions on this topic. Carbon dioxide leaves the atmosphere
when it is absorbed by plants and by the ocean, of course. What is
worrisome is that some parts of the ocean are saturated with carbon dioxide
and are releasing it back to the atmosphere.
Ref: J.S.Levine (editor): GLOBAL BIOMASS BURNING: ATMOSPHERIC,
CLIMATIC, AND BIOSPHERIC IMPLICATIONS, The MIT Press (1991)
Jane Jackson, Prof. of Physics, Scottsdale Comm.College (on leave)
Box 871504, Dept. of Physics, Arizona State Univ., Tempe, AZ 85287-1504.
phone:(602) 965-8438 fax: 965-7331 e-mail: jane.jackson@asu.edu
Modeling Workshop Project: http://modeling.la.asu.edu/modeling.html