Instant Notes: Plant Biology

deposits are extracted from the ground and burned, large amounts of CO 2 are

released to the atmosphere. Destruction of forests reduces fixation of CO 2 and

gives further CO 2 release.

Rising global CO 2 levels have a number of consequences, the chief of which is a

net rise in global temperature. Solar radiation travelling through the earth’s

atmosphere is partly reflected back into space by the earth’s surface and clouds;

however, CO 2 in the atmosphere absorbs some of the infra-red radiation which

would escape. This makes the earth warmer; the degree of warming increasing

with more CO 2. While it is very hard to estimate precisely the degree of

warming experienced as a result of rising CO 2 , and the presence of other green-

house gases such as methane may be very significant, a rise of about 0.5ºC in

global mean surface temperature has occurred over the last quarter century.

Altered average temperatures have been accompanied by more extreme

weather changes. These include earlier and later frosts and heavier rainfall in

some areas and drought in others. With drought comes the possibility of fire

and these have been widespread, particularly in the Asia/Pacific region. Rising

sea level accompanied by melting ice-shelves in the Arctic and Antarctic are also

Global warming

K5 – Contribution to carbon balance and atmosphere 181

Land

plants

(560)

Destruction

of vegetation

Soils

(1500)

Atmosphere

(720)

38 000

Ocean

107 105

120

60 2

60

Coal/oil/gas

Resp

iratio

n

Pho

tosy

nthes

is

5

Fig. 1. A global carbon cycle. Pools of carbon are expressed as 10^15 g of carbon and fluxes

as 10^15 g year–1of carbon.

340

310

1960 1970

Year

1980

CO

concentration (ppm) 2

Fig. 2. Mean monthly atmospheric CO 2 concentrations measured at Muana Loa, Hawaii.

(Data obtained from the National Oceanic and Atmospheric Administration (NOAA), Climate

Monitoring and Diagnostic Laboratory (CMDL), Carbon Cyde-Greenhouse Gases, Boulder,

CO, USA.)