Environmental Engineering Reference
In-Depth Information
currents can change suddenly or ice sheets dramatically break up. These lag factors make
it more difficult to predict what changes will happen and when.
FUTURE CLIMATES
From this information, can we say what the future climates of Earth may be like?
Numerous predictions have been made. Climatic models have been used to investigate
the effects of known or highly likely changes in the near future. They would include the
effects of an atmosphere with more greenhouse gases in its composition, together with
the orbital variations that we know will take place over the next 100,000 years (Figure
9.16). Output from the orbital models indicates that climates as warm as those of today
are relatively rare and suggests that, other things being equal, the global climate should
start to change more rapidly. Unfortunately because of the very different time scales of
operation it is difficult to incorporate astronomic, oceanic and atmospheric effects into
the same model. At present any discussion of their joint impact relies on informed
judgement and speculation. Impact will also be influenced by the level of economic and
social development of a country. Sea-level rise could have different consequences for a
country like the Netherlands than for the Maldive Islands.
Our uncertainty about the future climate is based upon the many different forcing
factors, some linear and some non-linear, which operate over many different time scales,
all superimposed on each other and each operating over a different time cycle.
Consequently it is almost impossible to tell how long any trend we are able to identify
will persist. We can only guess at what even the immediate future holds.
IMPLICATIONS OF GLOBAL WARMING
key concepts
Although debate continues, there is growing concern that the observed increase in carbon
dioxide and other greenhouse gas levels is likely to lead to a global increase in
temperature of between 2° C and 4° C over the next century. Global circulation models
predict that the increase is not likely to be uniform; some areas will have a slightly lower
increase and other parts considerably more. Unfortunately this does not mean that we can
look at areas which already experience such temperature levels and assume that
conditions there indicate the future climate. In addition to mean annual temperature
change, it is likely that minimum temperatures will increase more than maximum
temperatures, so that the temperature range will decline. Precipitation is very difficult to
predict; it may increase in some areas and decrease in others, but the effect of increased
evaporation through higher temperatures will be decreased soil moisture levels. In
Britain, it has been argued, winter precipitation should increase but there may be a
decline in summer precipitation. Storminess may increase in winter in temperate latitudes
and there could be an increase in tropical storms as sea surface temperatures increase. All
these predictions are conditional: no one is really sure what other climatic implications
may result from a rise in global mean temperature.
Other predictions are more certain. If there is an increase in temperature the oceans
will get warmer and expand
so mean sea level will rise
In addition
with warmer
