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Global Warming, Part 1: Recent and Future Climate
Learning Objectives
After reading this chapter, students should be able to:
• Know that the global climate fluctuates on small timescales of years to decades, and
that scientists are still not sure about the causes of these short-term fluctuations
• Know the basic shifts in climate during the last 10,000 years, including the
Holocene Climatic Optimum, the Little Ice Age, and the Medieval Warm Period
• Be aware of the short-term influence of volcanoes on climate
• Understand the evidence for solar variability, its connection to the 14C record, and
its possible connection with climate
• Understand the implications these past climate fluctuations have on our analysis of
changes that could occur as a result of anthropogenic global warming
• Know the relative sizes of different carbon reservoirs and fluxes, in particular the
size of anthropogenic fluxes compared to natural fluxes
• Know the timescales of the various CO2 removal processes
• Understand the chemistry of CO2 uptake in the oceans
• Know some of the projections for future CO2 concentrations and the predicted
climatic implications of global warming
• Realize the level of uncertainty that exists in these models, and the sources of these
uncertainties
• Realize that anthropogenic gases other than CO2 contribute to the greenhouse effect
• Understand the long-term implications of global warming, i.e., on time scales of
centuries to thousands of years, and its potential for causing changes in deep ocean
circulation patterns
Review Questions
1.) What is the Holocene epoch?
2.) What are proxy data? Describe several examples of proxy climate data.
Proxy data are data used to determine what a measurable quantity was at a time or
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3.) Briefly describe the Younger Dryas, the Holocene Climate Optimum, the European
Medieval Warm Period, and the Little Ice Age.
The Younger Dryas Event and the Little Ice Age are both periods of rapid cooling.
The Younger Dryas Event occurred around 10,500 years ago, and the Little Ice Age
4.) How do volcanoes affect climate?
Volcanoes release gases into the atmosphere which have varying effects on the
5.) What are sunspots? Why are they thought to have a possible effect on climate?
Sunspots are relatively cool, dark blotches that appear on the surface on the Sun.
They are thought to be caused by changes in the Sun’s magnetic field and are
6.) How does the amount of CO2 produced by fossil fuel consumption compare to the
natural flux of CO2 in the carbon cycle?
The CO2 produced by fossil fuel consumption is ~ 7.5 Gton(C)/yr, while the flux
7. What are the major processes that can remove CO2 form the atmosphere? What
are the approximate time scales for these processes to be effective?
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8. What is the size of the fossil fuel reservoir compared with the atmospheric CO2
reservoir?
9. Why does the ocean have a limited capacity for CO2 uptake?
10. By how much is global temperature predicted to rise over the next century?
Critical-Thinking Problems
1.)
a. The present atmosphere contains approximately 700 Gton(C) in the form of CO2.
Earth’s total recoverable fossil fuel reserves contain at least 4200 Gton(C), mostly
in the form of coal. (We shall use the value 4200 Gton(C) to be specific.) At
present, about half the CO2 produced by the burning of fossil fuels stays in the
atmosphere. The other half dissolves in the oceans or is taken up by the terrestrial
biosphere. If this ratio remained constant and we burned up all of our fossil fuels
instantaneously, by how much would atmospheric CO2 concentrations rise?
(Express your answer in terms of the new CO2 level divided by the old one.)
The CO2 level would increase by 4200 Gton(C) / 2 = 2100 Gton(C). The new
atmospheric concentration would be:
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b. Climate models predict that each doubling of the atmospheric CO2 concentration
will cause the mean global temperature to increase by 1.5ºC-4.5ºC. (The range is
due largely to uncertainties about how clouds will respond.) By how much would
the mean temperature increase for the scenario described in part (a)? Express
your answer as a temperature range in degrees Celsius and in degrees Fahrenheit.
Increasing the CO2 concentrations to 4 times their present-day levels would
c. The actual problem of global warming could be more severe than we have just
calculated. Forests and soils together contain an additional 2100 Gton(C) of
carbon that might go into the atmosphere if deforestation is not prevented. The
ocean becomes more acidic as it absorbs CO2, so it might not be able to continue
taking up as much CO2 as it has been until now. If we burned up all our fossil
fuels and deforested one-third of the globe without losing any CO2 to the ocean
(or to CO2 fertilization) by how much would atmospheric CO2 and temperature
increase?
The increase in CO2 levels would be
2.) The atmospheric CO2 concentration is currently increasing by about 1.9 ppm/yr.
How many gigatons of carbon are being added to the atmosphere each year?
(Hint: The total mass of the atmosphere is 5 × 1018 kg, and its mean molecular
weight is about 29. You will need to do the calculation in moles and then convert
back to mass units.)
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3.) The surface ocean contains about 2.6 × 1016 liters of water with a carbonate ion
content of about 2 × 10-4 mol/L. The deep ocean contains about 1.4 × 1021 L of
water with a carbonate ion content of roughly 9 × 10-5 mol/L. If each mole of
carbonate reacts with 1 mole of CO2 according to the reaction
CO2 + CO3= + H2O Æ 2 HCO3–
what percentage of the fossil fuel reservoir, 4200 Gton(C), can be neutralized by
the surface ocean? By the deep ocean?
The fossil fuel reservoir contains 4200 Gton(C) = 4200 × 1015 g(C). This is
Resource Guide
Video/Film:
An Inconvenient Truth