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Feedback Effects
Tue Nov 18, 2003
Listen in RealAudio 
Hi, I'm Bryan Yeaton and this is The Weather Notebook's weekly segment on global climate
change.
Climate, of course, is a very complicated system, largely due to what are called "feedback
effects"--changes in one part of the system can cause effects in another. Warmer temperatures,
for example, will melt arctic ice, which means less white surface available to reflect
sunlight back to space. That, in turn, will warm the surface further and amplify the ice melt,
and so on.
Feedback effects can go both ways. At first glance climate change was expected to worsen the
problem of ground level ozone, which is bad for human health. This ozone is produced when
nitrous oxides from our smokestacks and tailpipes combine with hydrocarbons, such as isoprene,
most of which are produced by trees and other plants. Initially scientists calculated that
ozone levels could increase by up to 30 parts per billion by the year 2090, an unhealthy
amount when many parts of the world already approach or exceed the World Health Organization's
recommended maximum of 60 parts per billion.
But the ozone issue, at least, might not be as bad as expected, due to a negative feedback
effect. That's because tree and plant species will be migrating due to future climate change.
Significant forest loss is predicted for the Amazon, and New England maple trees will be
migrating north. The result of this vegetation shift is that a much smaller area of the planet
may experience increased ground-level ozone as the climate changes.
Of course, this tree migration may produce many other feedback effects, so you can expect to
hear more about it as scientists try to better understand all the details of climate
change.
Science writer David Appell contributed today’s story. The Weather Notebook is funded by the
National Science Foundation, and Subaru.
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