Laboratory Manual for Introductory Geology 4e

EXERCISE 18.3
Name:
Course:
Assessing Human Contributions to Global Warming (continued)
Section:
Date:
Now examine the curves in the right-hand graph on the previous page showing changes in greenhouse gas concentrations over
the past 2,000 years.
(g) Describe the variation in greenhouse gas concentrations over the first 1,700 years of the time span shown.
(h) Concentrations increased dramatically in the mid-18th century, a major milestone in human technological
development. What happened at that time that could have had an effect on greenhouse gas concentrations?
(i) What do these data say about whether humans play a role in global warming? Explain.
CO 2
, N 2
O, and CH 4
are natural greenhouse gases, but they are also released when humans burn fossil fuels (wood, coal,
oil, natural gas). In addition, several synthetic gases not found in nature are also powerful greenhouse gases—far more
powerful than the natural gases, and with longer residence times in the atmosphere, as detailed in the table below.
Greenhouse gas potencies of selected natural and synthetic gases.
Atmospheric concentration Greenhouse gas potency Residence time
Gas
Pre-1750 Current (compared with CO 2
) in atmosphere (years)
Carbon dioxide (CO 2
) 280 ppm 407 ppm 13 100–300
Methane (CH 4
) 722 ppb 1,850 ppb 283 12.4
Nitrous oxide (N 2
O) 270 ppb 328 ppb 2653 121
Perfluoromethane (CF 4
) 40 ppt 80 ppt 5,7003 .50,000
Sulfur hexafluoride (SF 6
) 0 4.2 ppt 22,2003 3,200
Sources: U.S. EPA, U.S. DOE, NOAA.
ppm 5 concentration in parts per million by volume; ppb 5 parts per billion; ppt 5 parts per trillion.
(j) What does this information add to your answer to question (h) above?
18.2 CHANGES IN THE EARTH SYSTEM
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