326 ■ CHAPTER 18 General Principles of Ecology
ECOLOGY
30,000 square miles of rainforest. In 2005 alone,
fires increased 20-fold in the year following the
drought. “It was a huge increase,” says Michael
Coe, a researcher at the Woods Hole Research
Center in Massachusetts and one of Balch’s collab-
orators. “And if humans are increasing drought
frequency, that’s going to be a big problem.”
Humans, researchers suspect, are increas-
ing the number and intensity of droughts in the
Amazon through climate change. It’s important
to distinguish between “climate” and “weather.”
We a t her refers to short-term atmospheric
conditions in a limited geographic area, such
as today’s temperature, precipitation, wind,
humidity, and cloud cover. Climate describes
the prevailing weather of a region over relatively
long periods of time (30 years or more). Organ-
isms are more strongly influenced by climate
than by any other feature of their environment.
On land, for example, features of climate such
as temperature and precipitation determine
whether a particular region is desert, grassland,
or tropical forest.
Climate change, then, is a large-scale and
long-term alteration in Earth’s climate, and
it includes such phenomena as global warm-
ing, change in rainfall patterns, and increased
frequency of violent storms. Although Earth
has gone through many changes in its average
climate over its 4.6-billion-year history, the speed
of the change that has taken place in the past
100 years is without precedent in the climate
record. Climate change in recent history has been
caused to a large extent by human actions, and its
consequences are likely to be negative for people
and ecosystems around the world (Figure 18.5).
“There are a lot of indications that climate
change causes increased drought events, caus-
ing increased fire events,” says Balch. “It’s hard to
predict the future, but that’s definitely the trend.”A Warmer World
The terms “global warming” and “climate change”
are related but not synonymous. Global warm-
ing is a significant increase in the average surface
temperature of Earth over decades or more.
Temperature on Earth is generally determined
by the angle at which sunlight strikes the planet.
Sunlight strikes Earth most directly at the equa-
tor, but at a more slanted angle near the North andTo prevent fires in their two experimental
plots from spreading, each plot was protected by
a firebreak—a perimeter around the plot, several
meters wide, cleared of all plants, sticks, grasses,
and debris. Once the plots were prepared, it was
time to set the fires. The team walked along
10 kilometers of trail cutting through the plots,
dripping flaming kerosene from special tanks
and watching the forest burn.
The experiment began not a moment too soon.
In 2005, the Amazon experienced an extreme
drought. Experts called it a “hundred-year
drought,” meaning that such a drought is expected
to occur, on average, only once in a century. But
just five years later, in 2010, there was another
hundred-year drought, this one even more wide-
spread and severe. And in both cases, extensive
wildfires followed the drought, destroying overFigure 18.4
Scientists take measurements before a planned burn in
the Amazon
MICHAEL COE
Michael Coe is a hydrologist and leader of the
Amazon Program at the Woods Hole Research
Center in Massachusetts. He investigates how
humans affect the water and energy balance in
tropical South America.