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Cloud Forest
Tue Apr 15, 2003
Listen in RealAudio 
Hi, I'm Bryan Yeaton for The Weather Notebook's weekly segment on global climate
change. The first signal or "fingerprint" of global warming is showing up in some of
earth's most extreme and fragile environments.
Take Costa Rica's Monteverde cloud forest as one striking example. Weather and
topography have collaborated to produce this unique ecosystem: when trade winds are
forced to rise over Costa Rica's central mountain range, they condense and release
their moisture in swirling fogs that cling to the mountain slopes. But since the mid
1970s, something strange has been happening, the cloud forest has become
significantly less cloudy.
The meteorological explanation is fairly straightforward. Since air flowing upslope is
warmer and drier than it used to be, the altitude at which condensation occurs has
risen. When it was first detected, this phenomenon was attributed simply to global
warming: warmer air, warmer oceans, higher condensation altitudes. But recently
scientists have also come to believe that clearing of nearby lowland forests also plays
a role. Land stripped of its trees tends to warm up and dry out faster, resulting in less
available moisture to be carried up to the cloud forest.
Together, global warming and local deforestation have altered this fragile habitat
sufficiently to account for the extinction of the golden toad in the late 1980s.
There's one other species that may be affected: humans. Eco-tourism is big business
in Costa Rica, and local businesses are wondering if people will visit a cloud forest
without any clouds?
Our series on global climate change is funded by the New England Science Center
Collaborative and the Roy A. Hunt Foundation.
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