Climate and the Biosphere

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“People had long speculated that the climate might be altered
where forests were cut down, marshes drained or land irrigated.
Scientists were skeptical.”
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So far, the only three climate books I’ve read
cover-to-cover are Spencer Weart’s — The
Discovery of Rapid Change, and The Discovery of
Global Warming — and Mickey Glantz’s Currents of
Change.  Each does a great job, in widely
accessible terms,  of showing how and why
scientists themselves had a hard time coming to
grips with the processes that still confuse so
many ordinary people today.

Both of Weart’s books are free online. Here’s a
couple URLs and some snips from one chapter of
his The Discovery of Global Warming.
Lance

The entire book is available free at American Institute of Physics website
<http://www.aip.org/history/climate/>

Chapter Six
Biosphere: How Life Alters Climate
whole chapter here: <http://www.aip.org/history/climate/biota.htm>

Chapter summary:

People had long speculated that the climate might
be altered where forests were cut down, marshes
drained or land irrigated. Scientists were
skeptical. During the first half of the 20th
century, they studied climate as a system of
mechanical physics and mineral chemistry,
churning along heedless of the planet’s thin film
of living organisms. Then around 1960, evidence
of a rise in carbon dioxide showed that at least
one species, could indeed alter global
climate-humanity. As scientists looked more
deeply into how carbon moved in and out of the
atmosphere, they discovered many ways that other
organisms could also exert powerful influences.
Forests in particular were deeply involved in the
carbon cycle, and from the 1970s onward,
scientists argued over just what deforestation
might mean for climate. By the 1980s, it was
certain that all the planet’s ecosystems were
major players in the climate changes that would
determine their own future.

Selected excerpts:

” In 1966, when the U.S. National Academy of
Sciences arranged a study of possible climate
change, the panel mainly considered urban and
industrial influences, that is, deliberate human
excavation and emission of materials. The experts
remarked that changes involving living creatures
in the countryside, such as irrigation and
deforestation, were “quite small and localized,”
and set that topic aside without study.(15)

“In 1975,  veteran climate modeler Jule Charney
proposed that climate change was acting as man’s
accomplice. Noting that satellite pictures showed
a widespread destruction of vegetation in the
Sahel from overgrazing, he pointed out that the
barren clay reflected sunlight more than the
grasses had. He figured this increase of albedo
(surface reflectivity) would make the surface
cooler, and that could change the pattern of
winds so as to bring less rain. Then more plants
would die, and a self-sustaining feedback would
push on to full desertification.(18)

“Charney was indulging in speculation, for
computer models of the time were too crude to
show what a regional change of albedo would
actually do to the winds. It would be a few more
years before models and observations demonstrated
what had long been suspected – surface vegetation
is an important factor in the climate.”

“Despite the confusing details, scientists
grasped the truth of Charney’s main lesson. Human
activity could change vegetation enough to affect
albedo, and a change in albedo could interact
with other factors to change climate. More
generally, the biosphere did not necessarily
regulate the atmosphere smoothly through
“negative” feedbacks. It could itself be a source
of the kind of “positive” feedbacks that brought
instability.(19*)”

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