Energy and Human Ambitions on a Finite Planet, 2021a

9 Climate Change 159
2. How many kilograms of CO 2 are produced from consuming a
40 L tank of gasoline? Compare the result to typical human mass.
Gasoline is about 0.75 kg/L.
3. Typical household electricity use in the U.S. is about 30 kilowatthours
(kWh) per day. If the electricity is produced by a natural gas
plant operating at 40% efficiency, each household requires 75 kWh
of energy from natural gas each day. Converting this to Joules, <strong>and</strong>
using the intensity of 49 g/MJ from Table 9.1, how much CO 2 is
produced daily to supply a house with electricity from a natural
gas source?
4. Americans use energy at an average rate of 10,000 W. Convert this
to Joules in a day, then MJ, then use a representative number 75
in the right-h<strong>and</strong> column of Table 9.1 to estimate an approximate
CO 2 emission per American per day, in kg. Compare this to the
mass of a typical person.
75: . . . considering that we use a mix
5. Getting more specific, Americans, on average, get about 320 MJ
per person from oil each day, 265 MJ from gas, <strong>and</strong> 110 MJ from
coal. Based on the CO 2 mass per energy column in Table 9.1, how
much mass, in kg, of CO 2 does an American produce per day from
each of these sources, <strong>and</strong> in total? Compare this daily emission to
the mass of a person.
6. If carbon dioxide emission is a chief concern, switching from a
coal-fired electricity plant to natural gas input is still a use of fossil
fuels, but natural gas produces less CO 2 per energy unit than coal
(Table 9.1). By what factor would CO 2 emissions be reduced if
replacing all energy 76 we now get from coal with energy from
natural gas?
76: E.g., Even swap, MJ for MJ
7. Divide the total CO 2 increase by the annual CO 2 increase in Figure
9.3 to get a timescale in years. Compare this timescale to the period
over which we have been burning fossil fuels (e.g., Figure 9.2). Do
they agree? If not, what reason would you offer?
8. The right-h<strong>and</strong> panel of Figure 9.3 is an accumulation of the values
on the left-h<strong>and</strong> side—representing the area under the left-h<strong>and</strong>
curve, for instance. Since the gas trend on the left looks like a
triangle, it is easy to approximate its area. 77 Does the result match
the right-most value for gas in the right-h<strong>and</strong> plot?
9. According to the fossil fuel history shown in Figure 9.2, the world
currently gets energy from coal at a rate of 5 TW. From this, figure
out how many ppm v /year we add in CO 2 from coal, following the
outline in Table 9.2 <strong>and</strong> Box 9.1. Use a typical coal energy density
of 6.5 kcal/g <strong>and</strong> a mass ratio of 3.67 CO 2 g/g. 78 The result should
match information gleaned from Figure 9.3.
77: Multiplying ppm v /yr (height) times
years (base) gives units of ppm v , matching
the plot on the right.
78: ...orequivalently, 135 g/MJ
10. What is the most direct <strong>and</strong> convincing response to a “climate
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.