Inside Iowa State: Iowa State University

INSIDE IOWA STATE
February 1, 2002

Seeing the forest

"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."