17Precise quantification of the contemporary abundance of atmospheric CO 2 was initi-
ated by Charles David Keeling at the Mauna Loa Observatory (MLO) in Hawaii during
March 1958, as part of the International Geophysical Year (IGY) program (Keeling
et al. 1976 ). On the first day of measurement, an atmospheric CO 2 abundance of 313
parts per million (ppm) was recorded.^12 The MLO CO 2 record is a signature accom-
plishment of the IGY, carried out from July 1957 to December 1958 and characterized
by international cooperation on many scientific fronts. The ability of nations such as
the United States and the Soviet Union to collaborate on IGY, despite the Cold War,
serves as an inspiration for the level of international cooperation that will be needed to
address the consequences of rising GHGs recorded at the Mauna Loa observatory.
On the day this sentence was written, atmospheric CO 2 at MLO was 407.66 ppm.
This CO 2 reading amounts to a thirty percent increase relative to Keeling’s first
(^12) Mixing ratio denotes the fraction of all air molecules that exist as a particular compound.
Keeling’s initial observation means 313 out of every million air molecules were present as CO 2.
The history of the Mauna Loa Observatory as well as an account of this initial observation are at
https://scripps.ucsd.edu/programs/keelingcurve/2013/04/03/the-history-of-the-keeling-curve
32101
∆T (°C), 1959 to 2012
0
2
5
10
15
20
25
Altitude (km)
30°S to 30°N
Stratosphere
Troposphere
Fig. 1.5 Temperature change profile, 1959–2012. Temperature difference, 1959–2012, based on
analysis of radiosonde observations acquired between latitudes of 30°S and 30°N (positive values
indicate warming). After Sherwood and Nishant ( 2015 ) except we use altitude, rather than pres-
sure, for the vertical coordinate. See Methods for further information
1.2 The Anthropocene