Study Guide – Chapter 19 – Climate Change and Ozone Depletion
The Earth has undergone many
periods over the last 900,000 years, and for
the last 10,000, things have been pretty calm and productive, both for humans and the world’s
As you can see in Figure 19-2, however, the most recent part of the last 1,000 years
has seen significant warming; note in the figure that the planet has been as warm as it is now many
times, but this much warming over such a short time period seems to be something new.
We can construct these temperature histories from radioisotopes in rocks, fossils, and ocean
sediments, bubbles of air trapped in ice, pollen from plants deposited long ago, tree rings, insects and
minerals in 1000-year old bat dung; in short, there are many methods to investigate the temperature
history of the planet, and almost all of these are telling the same story.
We talked in class about the
, and the primary greenhouse gasses CO
and nitrous oxide (along with water vapor).
Note the concentration of CO
in the atmosphere in Figure
19-3, and the concerns by atmospheric scientists that we need to make sure that CO
below 450 ppm, a
(think threshold effect) that could cause unavoidable changes in
climate for hundreds to thousands of years.
Is it worth the risk to ignore these warnings, and the
models they are based on
Although methane emissions seem to have leveled off since 1990, they
are expected to rise again as increasing global temperatures melt the permafrost, glaciers, and ice
caps, which releases more trapped methane, which increases the temperature, which melts the ice
and releases more trapped methane, and on and on (think positive feedback).
Note also that a
molecule of nitrous oxide (increasing with development of modern agriculture and nitrogen-based
inorganic fertilizers) is 3-10 times worse than CO
in terms of trapping hear, and methane is 22 times
We looked at some of the findings of the report prepared by the
Intergovernmental Panel on
Climate Change (IPCC)
Although many industries refuse to admit the anthropogenic
contributions to the current warming trend, the book talks about several lines of evidence that support
the IPCC conclusions, e.g., rising temperatures, increasing CO
concentrations, rising arctic
temperatures, shrinking glaciers and sea ice, and increasing sea level.
Again, some of these factors
can amplify (positive feedback) or dampen changes in global warming or cooling.
of them are amplifiers.
The Science Focus on pages 502 and 503 shows projected heating by 2100,
note that the scale is fairly small (about +1.8 to +4.2 degrees Celcius in Figure 19-B), but the effects
of these small changes in temperature could be catastrophic, or at least planet-altering.
Given that the stratosphere has been cooling since 1975