Geoscience Reference
In-Depth Information
You might naturally ask why the United States generates any elec-
tricity from coal if it is so expensive. The answer is that the short-run
costs of coal are much lower than those for gas. For effi cient existing
plants, the costs of generation from natural gas are about twice as high
as those from coal. The difference between the long run and the short
run is the high capital cost of a new coal plant as compared to a new
natural gas plant. You will not be surprised that most new facilities be-
ing built or planned in the United States are gas fi red rather than coal
fi red. But the existing plants still have signifi cant emissions and will
operate for many years without environmental regulations or taxes.
What about removing CO 2 from the atmosphere? Natural processes
will eventually remove most of the CO 2 that human activities are adding
to the atmosphere. But these processes operate very slowly—on a time
scale of tens of thousands of years, which is too long to prevent rapid
climate change and its impacts. For example, suppose that countries
continue on a path of rapid emissions growth through 2100 and then
completely stop all emissions. CO 2 concentrations would remain well
above preindustrial levels for a millennium, and global temperature
would peak at around 4°C above 1900 levels. This striking result shows
the tremendous inertia in the carbon cycle and the climate system. 8
Perhaps we should consider a completely different approach to mit-
igation. Is it possible to remove the CO 2 after the fossil fuels have been
burned? This could take place either as an integrated process or after
the gases have entered the atmosphere. The advantage of postcombus-
tion processes is that we can continue to use the abundant fossil fuels to
power our economies and still reduce their climatic impacts.
The most promising of the postcombustion technologies today is
called carbon capture and sequestration (CCS). This technology would
burn fossil fuels (such as natural gas or coal) and then capture the CO 2 .
Burning is easy, while economical capture is diffi cult.
How would CCS work? The following description is based on a care-
ful study by a team of engineers and economists from MIT. 9 The basic
idea is simple. CCS would capture CO 2 at the time of combustion and
then ship it off and store it in some location where it would remain for
hundreds of years and thus not enter the atmosphere.
 
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