An Introduction to Environmental Chemistry

growth, energy use and mode of production. All predict a substantial increase in

atmospheric CO 2 during the next 100 years, with levels ranging from 500 to more

than 900 ppm by 2100. This factor-of-two range does not represent the whole of

the uncertainty since other scenarios outside the range used (both higher and

lower) are certainly possible. Furthermore, the environmental model used to sim-

ulate how much of the emitted CO 2 remains in the atmosphere assumes the envi-

ronmental system will behave as at present for the whole of the next century.

7.2.4 The effects of elevated carbon dioxide levels on global

temperature and other properties

So far we have examined the global cycling of carbon without paying attention

to the role CO 2 plays in the Earth’s climate. Although CO 2 is a minor compo-

nent of the atmosphere (see Section 3.2), it plays a vital role in the Earth’s radi-

ation balance and hence in controlling the climate. This is illustrated in Fig.

7.12a, which shows the wavelength emission spectrum of the Sun and the Earth,

at their effective radiating temperatures of about 5700°C and –23°C respectively.

Global Change 257

(a)

(b)

O 2 O 3 O 3 H 2 OCO 2

O 2 NO 2

Ultraviolet Visible Infrared

H 2 OCO 2 H 2 O

O 3

CH 4

0.1 0.5 1 5 10 50

Wavelength (mm)

5700 ∞C –23∞C

100

0

Absorption by atmosphere (%)

Fig. 7.12(a) Black body radiation spectra for the Sun (6000 K) and (not on the same scale) the Earth (250 K).
(b) Absorption spectrum produced by the principal absorbing gases. After Spedding (1974). Reprinted by
permission of Oxford University Press.