122 CHAPTER 5 How Ecosystems Work
©AP/Wide World PhotosCASE STUDY
Global Climate Change:
How Does It Affect the
Carbon Cycle?
Anthropogenic (human-caused) climate change is an established
phenomenon. Within the scientific community, the question is
no longer whether human-caused climate change will occur
but at what rate and with what effects, and what, if anything,
can we do about it. The biggest culprit in climate change is
an increase in atmospheric carbon dioxide (CO 2 ), which is
generated primarily through burning fossil fuels such as coal,
oil, and natural gas, as well as through the clearing and burning
of forests. During the past two centuries, the level of carbon
dioxide in the atmosphere has climbed dramatically, increasing
more than 20 percent just over the past 50 years. Atmospheric
CO 2 allows solar radiation to pass through but does not allow
heat to radiate into space. Instead, the heat is radiated back to
Earth’s surface. As CO 2 accumulates, it may trap enough heat to
warm the planet. (We say more about global climate change in
Chapter 9.)
Robert Socolow and Stephen Pacala of the Princeton
University Carbon Mitigation Initiative (CMI) suggest that
somewhere just below a doubling of atmospheric carbon from
preindustrial levels—600 billion tons in the early 1800s—lies the
amount of atmospheric carbon that, if accumulated, will lead to
the most dangerous of consequences. They propose that to keep
future atmospheric carbon below this doubling would require
generating 7 billion fewer tons of carbon each year by 2056 than
are currently expected.
Many people despair of ever finding a solution to this
enormous challenge. Socolow and Pacala, however, along
with other CMI researchers, propose a “stabilization wedges”
approach to solving the carbon emissions dilemma. In this
framework, carbon reductions can be thought of in terms of
“wedges,” each of which would result in a 1-billion-ton-per-year
reduction by 2056. A combination of any seven wedges would
put us on a path to avoid the critical doubling of CO 2. Socolow
and Pacala identify 15 technologies in five categories, any one
of which could serve as one of the seven wedges. Three of these
wedges are:
Increase the fuel economy of 2 billion cars from 30 to
60 mpg. Two billion cars are expected to be on the world’s
roads by 2056, each traveling an average of 10,000 miles
per year. If the typical car operates at 60 mpg, there will be
1 billion fewer tons of carbon generated each year than if
they operate at 30 mpg (see photo).
Install carbon capture and storage devices at 800 large
coal-fired power plants. Currently, the CO 2 produced from
burning coal is released to the atmosphere. If 90 percent of
the carbon released each year is instead captured and stored,
1 billion fewer tons will be released to the atmosphere.
Stop all deforestation and double the current rate of plant-
ing new forests. Deforestation worldwide currently releases
2 billion tons of carbon to the atmosphere each year. How-
ever, it is expected to slow to 1 billion tons per year without
intervention. To achieve a 1-billion-ton wedge below the ex-
pected amount would require significant efforts in both re-
ducing deforestation and increasing reforestation.Some scientists think we should abandon the con-
cept of keystone species because it is problematic. For
one thing, most of the information about keystone
species is anecdotal. Scientists have performed few
long-term studies to identify keystone species and to
determine the nature and magnitude of their effects on
the ecosystems they inhabit.
[START CC]- What is one example of mutualism?
of parasitism? - What is one example of a predator–prey
interaction? - What is the difference between interspecific
and intraspecific competition? - How does a keystone species affect its
ecosystem?
Hybrid vehicles such as this model of the Honda Insight allow
consumers to lower their gasoline consumption and thus reduce
their CO 2 emissions.✓✓THE PLANNER