Botkin Environmental Science Earth as Living Planet 8th txtbk

430 CHAPTER 20 The Atmosphere, Climate, and Global Warming
fierce reputation, were less able than the Inuit to adapt to
the cooling climate.
We do not know what caused the Medieval
Warm Period, and the details about it are obscured
by insufficient climate data to help us estimate
temperatures during that period. We do know that
it was relatively warm (in Western Europe). We can’t
associate the warming 1000 years ago with burning of
fossil fuels. This suggests that more than one factor can
cause warming. In this chapter we will explore climate
dynamics so you can better understand what may be
the causes of climate change and what might be the
best estimates of how it could affect life on Earth and
civilizations. 1–5
20.1 Fundamental Global
Warming Questions
The modern concern about global warming arose from
two kinds of observations. The first, shown in Figure 20.2,
is of the average surface temperature of the Earth from
1850 to the present. This graph shows an increase beginning
in the 1930s and accelerating, especially after 1960,
when the increase was about 0.2°C per decade.
The second kind of key observation is the measurement
of carbon dioxide concentrations in the atmosphere.
Of these, the best-known were made on Mauna
Loa Mountain, Hawaii, by Charles Keeling and are now
known as the Keeling Curve (Figure 20.3). Taken at 3,500
m (11,500 ft) on an island far from most human activities,
these measurements provide an excellent estimate of
the background condition of the atmosphere.
Here are the fundamental questions about global
warming:
What is the origin of known periods of rapid warming
in the geologic record? This fundamental question
is the subject of intense ongoing research and is not yet
solved.
Is the present rapid warming unprecedented or at least
so rare that many living things will not be able to respond
successfully to it?
To what extent, have people caused it?
What are likely to be the effects on people?
What are likely to be the effects on all life on Earth?
How can we make forecasts about it and other kinds of
climate change?
What can we do to minimize potential negative effects?
FIGURE 20.2 The temperature difference
between the average at the end of the 19th
century and the years between 1860 and
today. This graph shows the difference between
calculated world surface temperatures
for each year and the average at the end
of the 19th century. Temperature departure
refers to changes in mean global temperature
from some standard such as 1951–1980. Climatologists
studying climate change prefer,
in general, to look at the difference between
temperatures at one time compared to
another, rather than the actual temperature,
for a variety of technical reasons. (Source:
Hadley Meteorological Center, Great Britain.)
http://www.metoffice.gov.uk/corporate/pressoffice/myths/2.html)