165
temperature of the Earth, and how variations in atmospheric CO 2 concentrations
allow the Earth to warm or cool.
Despite Dr. Arrhenius’ best efforts we now understand that the onset of the ice
ages was caused by multiple factors, including the mechanics of the Earth’s orbital
cycles, changes in solar heat output, and variations in ocean currents, along with
changing carbon dioxide levels in the atmosphere. The climate we are in at present
is an interglacial period within a larger ice age that began approximately three million years ago (Ehlers and Gibbard 2011).
Although carbon dioxide levels in the atmosphere are not the sole cause of
climate shifts, changing the concentration of the gas does have an effect on the heat
budget of the Earth. One prominent source of CO 2 known even back in Arrhenius’
day is fossil fuel combustion. He made an interesting calculation in his carbon dioxide paper showing that burning the annual global production of coal (around 500
million tons in 1896 at the time of the article) could be expected to increase CO 2
levels in the atmosphere by about one part per thousand every year. This is actually
quite high, and the Earth would resemble Venus by now if the rate was real.
Arrhenius overestimated atmospheric CO 2 concentrations by not accounting for
substantial absorption by the oceans, incorporation into vegetation, and the increased
chemical weathering of rocks. Based on the measurements shown in Fig. 9.2, the
actual rate of CO 2 increase in the atmosphere is about 2 parts per million per year,
some 500 times lower than that predicted by Arrhenius. As an interesting aside, coal
production worldwide in 2013 was about 8701 million tons, or 7893 million metric
tons according to the most recent EIA data, more than 17 times greater than in
Arrhenius’ day.
There are other GHGs in addition to carbon dioxide. Prominent among these is
methane, the primary component of natural gas, and it is also generated by anaerobic biological processes. Methane is actually a stronger absorber of infrared radiation than CO 2 , but it is easily oxidized and is relatively short-lived in the atmosphere.
Other potent GHGs are the so-called ozone-depleting substances that include compounds such as chlorofluorocarbons (CFCs), widely used at one time as refrigerants
(Polvani et al. 2020). CFCs were identified in the late 1970s as the cause for the
dramatic deterioration of the ozone layer that protects the Earth from ultraviolet
radiation. They were banned worldwide in 1987 with the adoption of an international agreement called the Montreal Protocol. CFC levels in the atmosphere have
been slowly declining ever since, but with lifetimes of 52 years for CFC-11 and
102 years for CFC-12, it will take some time to clear them out (Solomon et al. 2014).
It is becoming increasingly obvious that human activities are affecting the
chemistry of the atmosphere. The behavior of carbon dioxide as a GHG is well
understood, even if its effects on the climate are complicated. The destruction of the
ozone layer by CFCs and the contribution of these gases to a warming atmosphere
are accepted as solid science. The ability of methane to trap heat is not in dispute.
Sophisticated mathematical models far more complex than anything Professor
Arrhenius could have imagined are predicting increased weather instability, warming of the polar regions, sea level rise, deadly heat waves, larger storms, and more
intense droughts. These predictions have been verified by actual observations in
9.2 Climate Contrarians
temperature of the Earth, and how variations in atmospheric CO 2 concentrations
allow the Earth to warm or cool.
Despite Dr. Arrhenius’ best efforts we now understand that the onset of the ice
ages was caused by multiple factors, including the mechanics of the Earth’s orbital
cycles, changes in solar heat output, and variations in ocean currents, along with
changing carbon dioxide levels in the atmosphere. The climate we are in at present
is an interglacial period within a larger ice age that began approximately three million years ago (Ehlers and Gibbard 2011).
Although carbon dioxide levels in the atmosphere are not the sole cause of
climate shifts, changing the concentration of the gas does have an effect on the heat
budget of the Earth. One prominent source of CO 2 known even back in Arrhenius’
day is fossil fuel combustion. He made an interesting calculation in his carbon dioxide paper showing that burning the annual global production of coal (around 500
million tons in 1896 at the time of the article) could be expected to increase CO 2
levels in the atmosphere by about one part per thousand every year. This is actually
quite high, and the Earth would resemble Venus by now if the rate was real.
Arrhenius overestimated atmospheric CO 2 concentrations by not accounting for
substantial absorption by the oceans, incorporation into vegetation, and the increased
chemical weathering of rocks. Based on the measurements shown in Fig. 9.2, the
actual rate of CO 2 increase in the atmosphere is about 2 parts per million per year,
some 500 times lower than that predicted by Arrhenius. As an interesting aside, coal
production worldwide in 2013 was about 8701 million tons, or 7893 million metric
tons according to the most recent EIA data, more than 17 times greater than in
Arrhenius’ day.
There are other GHGs in addition to carbon dioxide. Prominent among these is
methane, the primary component of natural gas, and it is also generated by anaerobic biological processes. Methane is actually a stronger absorber of infrared radiation than CO 2 , but it is easily oxidized and is relatively short-lived in the atmosphere.
Other potent GHGs are the so-called ozone-depleting substances that include compounds such as chlorofluorocarbons (CFCs), widely used at one time as refrigerants
(Polvani et al. 2020). CFCs were identified in the late 1970s as the cause for the
dramatic deterioration of the ozone layer that protects the Earth from ultraviolet
radiation. They were banned worldwide in 1987 with the adoption of an international agreement called the Montreal Protocol. CFC levels in the atmosphere have
been slowly declining ever since, but with lifetimes of 52 years for CFC-11 and
102 years for CFC-12, it will take some time to clear them out (Solomon et al. 2014).
It is becoming increasingly obvious that human activities are affecting the
chemistry of the atmosphere. The behavior of carbon dioxide as a GHG is well
understood, even if its effects on the climate are complicated. The destruction of the
ozone layer by CFCs and the contribution of these gases to a warming atmosphere
are accepted as solid science. The ability of methane to trap heat is not in dispute.
Sophisticated mathematical models far more complex than anything Professor
Arrhenius could have imagined are predicting increased weather instability, warming of the polar regions, sea level rise, deadly heat waves, larger storms, and more
intense droughts. These predictions have been verified by actual observations in
9.2 Climate Contrarians