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significant role. More than a century ago, Arrhenius (1896) already identified this
role in the Earth
s temperature control. Ice core studies reveal that on millennial time
scales, changes in CO
2
content recorded are highly correlated with changes in tem-
perature, although some temperature changes have occurred without a significant
CO
2
concentration change, but the opposite does not appear to have happened
(Falkowski et al., 2000). Less pronounced roles are played by CH
4
,N
2
O (nitrous
oxide), and several types of chlorofluorocarbons (CFCs) and SF
6
. It is the CO
2
,
CH
4
,N
2
O, and CFC concentrations in the atmosphere upon which man
'
'
s industrial
(a)
400
350
350
300
1
1800
1900
Year
2000
300
0
250
(b)
2000
2000
1500
0.4
1500
1000
500
1800
1900
Year
2000
0.2
1000
0
500
FIGURE 1.3
Atmospheric concentrations of CO
2
,CH
4
, and N
2
O over the last 10,000 years
(large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols
with different grey shades for different studies) and atmospheric samples (light grey lines in
steep curve part, red lines in the original publication). The corresponding radiative forcings
(net solar energy flux to the earth) relative to 1750 are shown on the right-hand axes of the large
panels. (Source: Reproducedwithpermission fromIPCC(2007), figure 2.3; figure SPM.1. ©IPCC.)
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