Global Warming - Energy and the Environment - page 279

occurs cyclically around Christmas, hence the name El Nino. Recently, major El Ni nos occurred in
1957-1958, 1972-1973, 1976-1977, 1982-1983, the early 1990s, and 1997-1998. The benefits of
El Ni no are a richer anchovy harvest. The disadvantages are wide-reaching climatic effects, such
as cool, wet summers in Europe; increased frequency of hurricanes and typhoons in the western
Pacific, South China Sea, southern Atlantic, and Caribbean Sea; and heavy storms and precipita-
tion battering the eastern Pacific coast from Mexico to British Columbia. The 1997-1998 El Ni no,
which caused winter storms along the Pacific coast of North America with heavy precipitation,
mud slides, and resulting property damage, is a recent reminder of what may have been a periodic
natural event, but which could be exacerbated and made more frequent in the future with enhanced
global warming.
The sea level and climatic changes may cause considerable shifts in population centers and
distribution of agricultural and forestry resources, and they may require incalculable investments
in habitat and property protection.

10.3 GREENHOUSE GAS EMISSIONS

The increase of GHG concentrations in the atmosphere is a consequence of rising emissions of these
gases from anthropogenic sources. The most significant of these gases is CO 2 , but CH 4 , CFCs, and
N 2 O emissions also need to be considered, as well as changes in O 3 concentrations.

10.3.1 Carbon Dioxide Emissions and the Carbon Cycle

Because carbon constitutes a major mass fraction of all living matter, on earth there is an enormous
reservoir of carbon in the living biosphere and its fossilized remnant. Sedimentary limestone,
CaCO 3 , contains about 12% of its mass as carbon. This limestone originates in part from shells
and skeletons of past living creatures, and in part from precipitation from a supersaturated aqueous
solution of CaCO 3 .
There is a continuous exchange of CO 2 between the biosphere and atmosphere. Carbon dioxide
is absorbed from the atmosphere during photosynthesis of land vegetation and phytoplankton living
in oceans and other surface waters. Carbon dioxide is returned to the atmosphere during respiration
of animals and decomposition (slow combustion of carbonaceous matter) of dead plant matter and
animals.
Figure 10.7 shows the rates of carbon exchange between the biosphere and atmosphere and
between ocean and atmosphere, and it also shows emissions from fossil fuel combustion and forest
burning (Gt y − 1 ). The figure also shows the carbon reservoirs residing in biota and soil litter on
land (2000 Gt), dissolved in the ocean (40,000 Gt), in fossil fuels (5000-10,000 Gt), and in the
atmosphere (750 Gt). 8
The respiration and decomposition of land organisms emit about 60 Gt y − 1 of carbon into the
atmosphere, while photosynthesis absorbs about 62 Gt y − 1 . Thus, there is a small net absorption
of CO 2 from the atmosphere by land-based biota. The oceans and other surface waters absorb
92 Gt y − 1

of carbon by dissolution of CO 2 and by photosynthesis of phytoplankton. The oceans

8 Carbon and carbon dioxide will be used interchangeably in subsequent discussions. To convert from carbon
to CO 2 , multiply by 44 / 12 = 3 . 67.