50 / Basics of Environmental Science
Modelling on this scale requires massive computing power. Even when the fastest supercomputers
are used, the grid must be fairly coarse to keep the number of intersection points to a manageable
level. This means that some phenomena, such as cloud formation, must be greatly simplified,
because they occur on a smaller scale than the 100×100×10 km grid boxes. Most GCMs make
similar simplified allowances for the mixing of surface and deep ocean water, although the
latest ‘coupled’ models (CGCMs) treat the oceans as of complexity comparable to that of the
atmosphere.
GCMs are being improved constantly and scientific understanding of atmospheric and oceanic
processes is increasing rapidly, but much remains to be learned and estimates of the regional
consequences of a general warming vary widely. The IPCC finds, for example, that warming will be
reduced by 60 per cent or more over the northern North Atlantic and around Antarctica. The best
illustration of the uncertainties surrounding the calculations centres on water vapour. If the temperature
rises, more water will evaporate. Water vapour is a greenhouse gas, so this will accelerate the warming
trend, but a more humid atmosphere will also be a cloudier atmosphere. As water vapour condenses
to form cloud the latent heat of condensation, released into the surrounding air, also has a warming
effect, but clouds themselves may have either a warming or a cooling effect. Generally, clouds at low
level have a high albedo and, therefore, cool the surface, while high-level clouds absorb radiation
and have a warming effect. Most GCMs predict an increase in middle- and high-level cloud, with a
consequent warming effect, but an increase in cloud amount, with deeper cloud cover, might reduce
warming. It is important to know how much cloud will form and its type, but at present this cannot
be calculated for given atmospheric conditions.
Many climatologists accept there is a real possibility of global climatic warming due to an enhanced
greenhouse effect. As with many large-scale changes, there would be winners and losers. Were
climate belts to shift toward higher latitudes, which seems the most likely overall result, parts of the
Sahara and southern Russia would receive increased rainfall. They would benefit and their agricultural
output would increase. On the other hand southern Europe and the United States cereal belt might
become drier. If warming produced a rate of evaporation that exceeded the increase in the rate of
precipitation, soils would become more arid. It may be, however, that warming will be experienced
as a reduction in the fall of temperature at night, due to increased cloudiness, with little or no change
in daytime temperatures. In that event, nighttime frosts would become less frequent, soils would
become somewhat moister, and agriculture would benefit.
Environmentalists favour the ‘precautionary principle’. This holds that if there is a chance of adverse
change we should not wait until the risk can be scientifically confirmed before taking action to
minimize it. When world leaders agreed to reduce greenhouse-gas emissions at the 1992 UN
Conference on Environment and Development (the ‘Rio summit’) they did so in accordance with
this principle. There are critics of the principle, however, who point to the cost and difficulty of
pursuing policies that may prove unnecessary. The principle holds that if any innovation appears to
entail a risk of serious or irreversible harm to human health or the environment, then precautionary
measures should be taken to avert that risk. This seems to obtain even if the link between the innovation
and the harm has not been proven or if it is weak and the harm is unlikely to occur. It can be argued
that this weighs the possible advantages and disadvantages of innovation, but loads the scales in
favour of the disadvantages. This could have a paralyzing effect if the only way to determine whether
the risk is genuine is to undertake the innovation—which the possibility of risk forbids (HOLM
AND HARRIS, 1999). Not surprisingly, others disagree, maintaining that the principle does not
necessarily prohibit innovation but does encourage preventive action in the face of uncertainty
(RAFFENSPERGER ET AL., 1999). In this area, as in many others, the environmental science is
uncertain and its translation into political action far from simple.