Energy and Human Ambitions on a Finite Planet, 2021a

9 Climate Change 139
1. mass ratio: how many grams of CO 2 are produced per gram 1 of 1: ...oranymass/weight measure you prefer
input fuel;
2. carbon intensity: how many grams of CO 2 are produced per unit
of energy delivered.
While all forms produce a mass ratio of approximately 3 units of CO 2 for
every unit of fossil fuels, the lower energy density of coal together with
its slightly higher mass ratio 2 make it more than twice as carbon-intense
as natural gas.
Example 9.1.1 Roughly how much CO 2 is produced from each full
tank of gasoline in a car?
2: Coal produces more CO 2 per gram of
fuel because the other fossil fuels also contain
mass in the form of hydrogen, which
not only adds to energy production but also
does not end up in CO 2 .
A typical tank might hold about 50 L of gasoline (13 gallons). The
density of gasoline is 0.75 kg/L, so that one tank has a gasoline mass
of about 38 kg. Applying the simple <strong>and</strong> convenient factor-of-three
ratio of CO 2 mass to input fuel mass, we see that one tank of gasoline
will produce something like 110 kg of CO 2 —not a small amount!
9.1.1 CO 2 Measurements
Beginning in 1958, Dave Keeling of the Scripps Institution of Oceanography
began recording CO 2 concentration in the atmosphere from the top
of Mauna Loa in the middle of the Pacific ocean. 3 In addition to seeing
annual variation due to the seasonal cycle of photosynthesis, 4 he began
to see a steady year-by-year increase in the level. The measurements have
continued to the present, now known as the “Keeling Curve,” shown in
Figure 9.1.
3: ...farfrom continental influences
4: Plants seasonally absorb <strong>and</strong> then release
CO 2 as leaves grow <strong>and</strong> then die.
420
1.2
400
1.0
CO2 (ppmV)
380
360
340
320
300
280
1960 1970 1980 1990 2000 2010
−0.2
2020
year
0.8
0.6
0.4
0.2
0.0
Temperature rise ( ± C)
Figure 9.1: In blue (left axis), CO 2 measurements
from Mauna Loa (Hawaii) for the last
60 years, showing a relentless <strong>and</strong> accelerating
upward trend now at abut 2.6 ppm v
per year [50]. Seasonal variations due to
photosynthesis are seen on top of this trend.
Pre-industrial levels were around 280 ppm v ,
so that we have added about 130 parts per
million (ppm). Red dots (right axis) show
global average mean temperature records
over the same period [51]. Thus far, global
average temperature has risen about 1 ◦ C.
Note that the Kyoto Protocol in 1997 <strong>and</strong>
Paris Agreement in 2015 (Box 19.4; p. 320)
do not visibly curb the upward trajectory
of CO 2 emissions.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.