A Unique Experiment of Planetary Dimensions - Four Revolutions in the Earth Sciences - page 222

As if to ensure that no one missed Plass's conclusions, in 1953 Time ran an art-
icle saying that
this spreading envelope of gas around the earth, says Johns Hopkins Physicist Gilbert N. Plass,
serves as a great greenhouse. Transparent to the radiant heat from the sun, it blocks the longer
wave lengths of heat that bounce back from the earth. At its present rate of increase, says Plass,
the CO 2 in the atmosphere will raise the earth's average temperature 1.5° Fahrenheit every 100
years. 6
In his review three years later, Panofsky would refer to Ångström's work but not
Hulburt's.
Contaminating the Atmosphere
By the mid-1950s, the big question mark was how much CO 2 the oceans had ab-
sorbed and how long a molecule of atmospheric CO 2 , once dissolved in the ocean,
would stay dissolved. A byproduct of Cold War research provided the answer.
Even more critical to national security than infrared radiation was the ability of
the United States to detect Soviet nuclear tests and to learn what type of bomb the
Russians had exploded. One important clue was the amount of an isotope of car-
bon, C-14, made in atomic explosions and present in the fallout. Fortunately, C-14
had other benefits.
C-14isradioactiveanddecayswithahalf-lifeof5,730years,allowingscientists
to use the isotope to date archeological objects. After about fifty thousand years,
C-14 decays to undetectable levels. It did not take scientists long to realize that
they could also use C-14 to trace the source and measure the age of carbon not just
in manmade objects but also in various earthly environments.
During the 1950s, Hans Suess (1909-1993), the grandson of Eduard Suess,
whomwemetin part2 , wasworkingfortheU.S.GeologicalSurveymeasuringthe
amountofC-14inancient treerings.Bycountingtheringsinward,scientists could
date them independently and use the result to calibrate the C-14 age obtained from
the same rings. In 1955 Suess reported that some modern wood revealed “con-
tamination” from “the introduction of C-14-free CO 2 into the atmosphere by arti-
ficial coal and oil combustion.” 7 But how did Suess know that the contaminating
“C-14-free CO 2 ” had come from burning fossil fuels? Coal and oil come from or-
ganismsthatdiedmillionsofyearsago.TheiroriginalC-14haslongsincedecayed
to undetectable levels. Thus the only source of C-14-free carbon in the atmosphere
is the combustion of ancient fossil fuels. This was the first proof that human activ-
ities are changing the composition of the atmosphere. The dilution of atmospheric