Laboratory Manual for Introductory Geology 4e

EXERCISE 18.3
Name:
Course:
Assessing Human Contributions to Global Warming (continued)
Section:
Date:
The graphs below provide more detailed records of temperature and greenhouse gas concentrations for the recent
past, during which the human population has been growing rapidly. The graph on the left tracks times when temperatures
were colder (negative values, shaded blue) or warmer (positive values, shaded light orange) than the average global
surface temperature in 1990.
Temperature (°C)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
–0.5
–1.0
Variation of temperature over time
Hotter than 1990 average
Cooler than 1990 average
1000
1100
1200
1300
1400
1500
Year
Average global
surface temperature
1600
1700
1800
1900
2000
Historical variations in temperature (left) and greenhouse gas concentrations (right).
CO 2 (ppm); N 2 O (ppb)
400
350
300
250
Concentration of greenhouse gases
Carbon dioxide (CO 2 ) ?
Methane (CH 4 )
Nitrous oxide (N 2 O)
0 500 1000 1500 2000
Year
2,000
1,800
1,600
1,400
1,200
1,000
800
600
CH 4 (ppb)
(c) Was temperature during the approximately 1,000-year span shown in the graph on the left mostly lower or higher
than in 1990?
(d) What does your answer to question (c) suggest about the temperature in 1990?
(e) What happened after 1990?
(f) Suggest a reason for this change.
(continued )
482 CHAPTER 18 LOOKING TO THE FUTURE