An Introduction to Environmental Chemistry

in the case of gas), rather than from the conversion of carbon to CO 2 , which

provides 80% of the energy when coal is burned.

Recent data on CO 2 inputs to the atmosphere from fossil fuels and other

anthropogenic sources have been compiled by the United Nations in their Energy

Statistics Database. Earlier data have been obtained from a variety of sources but

are more uncertain than the numbers for recent years. The results are presented

in Figs 7.5–7.7. In Fig. 7.5 the yearly inputs show a general increase over the

period since 1751 when records first become available. The data are plotted on

a logarithmic CO 2 emission scale in Fig. 7.6, which shows that the increase has

not always been at the same rate. Although for the periods 1860–1910 and

1950–70 the growth rate was close to 4%, during the two world wars, in the great

industrial depression of the 1930s and since the 1970s the rate of increase has

been closer to 2%. The slackening of emissions in the last 25 years is due to large

increases in the price of oil at the beginning of the period, conservation measures

generally and economic retrenchment in the 1990s. Wars, like depressions, are

apparently times of reduced economic activity. In Fig. 7.7 the data are plotted by

latitude for 1980 and 1989, which clearly show how strongly emissions are skewed

towards the industrialized mid-latitudes of the northern hemisphere. Over

the 1980s there is a clear shift in emissions southwards, as industrialization has

become more global. In the last year for which full data are available (1991), emis-

sions from fossil fuel burning, etc. are estimated to be 6.2 GtC yr-^1 , with an uncer-

tainty of less than 10%. Average annual emissions over the 1980s were 5.4±

0.3 GtC yr-^1. Finally, in Fig. 7.8 the record of fossil fuel emissions and atmos-

pheric concentration increase at Mauna Loa from 1958 to 2000 is shown. This

illustrates the variability of the increase in atmospheric CO 2 year by year (dis-

cussed later), and also that only about half of the carbon emitted stays in the

atmosphere to produce the yearly increase (as mentioned previously).

250 Chapter Seven

Carbon (tonnes

×^10

6 )

0

1000

2000

3000

4000

5000

6000

7000

Year

Solids

Liquids

Gases

Flaring

Cement

Total

1750 1800 1850 1900 1950 2000

Fig. 7.5Global CO 2 emissions from fossil-fuel burning (solid, liquid and gaseous fuels),

cement production and gas flaring for 1751–1999. After Marland et al. (2002).