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INSIDE IOWA STATE
February 1, 2002
Seeing the forest
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"Mike" Chen and his data. Photo by Bob
Elbert. |
by Skip Derra
Climate change scientists often swim in data. The "data tsunami" they face
results from the vastness, complexity and dynamics of Earth's weather. A
trap they sometimes can fall into is focusing too closely on one part of
their data and losing sight of its context -- sort of like not being able to
see the forest for the trees.
This is one reason Tsing-Chang "Mike" Chen, geological and atmospheric
sciences, looks at climate data differently than most of his peers. Chen,
who has been analyzing atmospheric and climate data for the past 33 years,
has made a career of taking seemingly unrelated data, finding the trend (and
relevance), explaining it, and then tying it to a grander picture of what it
means.
"Mike has a long history in working with climate data," said Gene Takle,
agronomy and geological and atmospheric sciences, who collaborates with
Chen. "From this experience and his unique methods of analysis, he is able
to see the reason behind some curious data, even though it has been there
all along staring us in the face."
The soft-spoken Chen recently did it again, this time taking on data that
suggested the opposite of what was the expected effect of deforestation in
the Amazon Basin.
Researchers have long thought that massive deforestation, such as that
taking place in the South American Amazon Basin, would result in general
warming and drying of that land. It would turn forestland into pastureland
and cause higher surface temperatures and less rainfall, they reasoned.
Computer models confirmed their hunch.
But the data didn't. Over a 40-year period (1950-1990), what actually
happened was a 20 percent increase in rainfall in the Amazon. How could this
be? Did it mean deforestation would have little or no effect on climate
change?
Chen took a longer look at the data, not only for the Amazon area, but all
over the world. He looked at "interdecadal changes," weather changes that
happen over decades of time. Until then, Chen said, the longest
deforestation experiment covered a period of 10 years.
"Many scientists have studied the effects of deforestation, but no one has
paid much attention to interdecadal change," Chen said. "This is a very
important component missing from the studies. It needs to be considered to
get a true reading of the effects of deforestation."
Chen found that a fundamental change had occurred in circulation patterns
over the Earth, a change that was muting the effects of the Amazon
deforestation. Chen began to see the forests' effect on the trees.
He could see that large-scale and long-term water vapor patterns were
converging on the Amazon, resulting in more rain there. He also saw less
rain in other tropical areas around the globe.
"Changes in global circulation is like studying a wave," Chen said. "There
may be water convergence in the Amazon, but there may be divergence in other
places."
These findings could be ominous for the region. If the rain pattern in the
Amazon reverses, as it is expected to do, then the "deforestation drying
that everyone expected will be made even worse by drying due to the reversal
of global circulation," Takle said. "There may be drought never before
experienced in this region."
The research by Chen, Takle and graduate students Jin-ho Yoon and Kathryn
St.Croix could help governments decide how to combat the coming effects of
deforestation.
Even if nothing is done in this instance, Chen has left a mark on global
climate change science. He now sees papers popping up about interdecadal
changes in weather patterns. A 1998 policy paper issued by the National
Research Council called "Decade to Century Scale: Climate Variability and
Change" is an even broader stamp of approval of work he helped pioneer.
"We started to do this type of research 10 years ago," he said. "Now it's
becoming popular."
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