Radiative Forcing of Climate Change - Climate Dynamics - page 157

2200

2000 Barrow CH 4

1800

Mauna Loa CH 4

Figure 10.2 Methane concentrations
measured at Barrow, Alaska (gray),
and Mauna Loa, Hawaii (black) in
ppb (parts per billion).

1600

1980 1990 2000 2010

1800

1600

1400

1200

1000

800

Figure 10.3 Methane
concentrations from the
Antarctic and Greenland ice
cores.

600

800 1000 1200 1400 1600 1800 2000

Year

Methane measurements are extracted from ice cores along with those of
CO 2 , and the Vostok core indicates that CH 4 varies with the glacial-interglacial
oscillation in the same way as CO 2 . Figure 10.3 shows CH 4 concentrations on
the millennial time scale from Greenland and Antarctic ice core measurements.
The pre-industrial CH 4 concentration was about 700 ppb (parts per billion)
and it is currently increasing exponentially at an average rate of about 1% per
year. This rise began in the 1700s as agricultural practices became more intense
and widespread and, later, as industrial activity developed.

NITROUS OXIDE (N 2 O)

Nitrous oxide, also known as “laughing gas” when used in high concentra-
tions as a sedative in the dentist's office, is a powerful greenhouse gas with a
long residence time in the troposphere of more than 100 years. Its concentra-
tions are estimated to be increasing at a rate of 0.26% per year (see Fig. 10.4) .
Pre-industrial values were about 260 ppb and they had risen to about 324
ppb in 2010.