Geoscience Reference
In-Depth Information
tration of atmospheric CO 2 was 288 parts of carbon dioxide
per every million part (ppm) of the overall atmosphere. as in-
dicated by the ice core record. By 2013, this proportion had
increased to almost 400 parts ppm. This may not seem like
much of an increase, but when you consider the importance of
atmospheric carbon dioxide in the natural regulation of global
temperature, it is important indeed. Some good news is that
U.S. carbon emissions in 2012 were at a 20-year low due to
the ongoing transition from coal-fired power plants to those
that burn natural gas. Nevertheless, global atmospheric CO 2
emissions will likely continue to rise in the foreseeable future
as densely populated developing countries such as India and
China, which between them contain about 2.3 billion people,
continue to industrialize and use the same fossil fuel power
sources that have worked so well for us.
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Age (thousands of years before present)
Reprinted by permission from Macmillan Publishers Ltd: E. Brook.
Paleoclimate: Windows on the greenhouse. Nature 2008; 453: 291-292.
Figure 9.28 Greenhouse gases and prehistoric temperature
for the past 800,000 years from the Dome C ice core in Ant-
arctica. This graph shows the close relationship between at-
mospheric temperature (red line), carbon dioxide (blue line), and
another (lesser) greenhouse gas (methane), which is the green
line. Temperature is the number of degrees above or below the
average modern surface temperature of about 14°C (55°F).
Is Anthropogenic Climate Change
Really Occurring?
The “million-dollar question,” of course, is whether or not
human-induced climate change is really occurring. You may
first ask: “Is the climate really warming?” With respect to this
initial question, the evidence strongly suggests that Earth is
indeed in a warming phase. You can see the evidence of this
warming by examining Figure 9.27, which shows the global
surface temperature anomalies, relative to the 1951-1980
mean, since 1880. The graph represents the composite trend
derived from meteorological stations around the world and
clearly demonstrates that the average global surface air tem-
perature increased over 1°C (1.6°F) since 1900. The first de-
cade of this century was the warmest ever observed, with nine
of the ten warmest years on record. In this decade, 2010 tied
2005 as the warmest year ever recorded globally. In the con-
tinental United States, 2012 was the hottest year the nation
had ever seen, with much of the country locked in a ferocious
drought during the summer and fall months. These increases
in temperature on both global and national scales correlate
very closely with the overall increase in atmospheric carbon
dioxide that has occurred at the same time. Much of the in-
crease in global temperature is attributed to an increase in av-
erage low temperatures because more longwave radiation is
held in at night.
With recent temperature trends in mind, it is pretty clear
that Earth's average temperature is warming. The more con-
troversial issue for some is the cause of this warming trend.
Skeptics argue that the apparent correlation between increased
atmospheric CO 2 and temperature could be coincidental and
that warming may be related to increased solar activity. In
fact, the geologic record shows that at other times in prehisto-
ry temperature increased rapidly and naturally, and we might
just happen to be living during another such period.
On the other hand, if we again examine the Quaternary, it
is obvious that the relationship between atmospheric CO 2 and
average global temperature is very close. This record is again
derived from ice cores where measurements of past levels of
atmospheric CO 2 can be measured from air bubbles trapped
in layers of glacial ice. The graph in Figure 9.28 shows this
comparison vividly for the past 800,000 years. These data
were acquired from the Dome C core in Antarctica, which
penetrated ice over 3200 m (~10,500 ft) thick. Look carefully
and notice how well oscillations in temperature (the red line)
compare with levels of atmospheric carbon dioxide (the blue
line) and methane (another greenhouse gas, represented by
the green line). As you can plainly see, there has been a very
close relationship between global climate and greenhouse
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5-year Running Mean
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Figure 9.27 Global surface temperature anomalies, relative
to the 1951-1980 mean, since 1880. The black line represents
the annual mean, whereas the red line is the 5-year running aver-
age. Note the rapid warming in the past 40 years. ( Sources : J.
Hansen, R. Ruedy, M. Sato, K. Lo. “Global Surface Temperature
Change.” Reviews of Geophysics 2010; 48:29p; 2011 Update by
NASA.)
 
 
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