Environmental Engineering Reference
In-Depth Information
British Isles were joined with the European mainland, and the polar ice sheets extended in Europe
as far as southern England and Switzerland, and in North America they extended to the Great Lakes
and southern New England.
The melting of ice caps may actually contribute the smallest fraction of sea level rise. This
is because of two competing effects. With increasing surface temperatures there will be more
evaporation and precipitation, including snowfall, which enlarges the ice caps. On the other hand,
some melting of the fringes of ice caps will occur. The net result may be a few centimeters of sea
level rise by the end of the next century.
In recent times, glaciers over the continents have been receding noticeably. Over the last
century this receding has contributed between 2 and 5 cm of sea level rise. If all glaciers outside
Antarctica and Greenland were to melt, the sea level rise would be in the range 40-60 cm.
The largest contribution to sea level rise will come from the thermal expansion of the surface
layer of the oceans. The estimation of this contribution is quite complicated, because the coefficient
of thermal expansion of water is a function of temperature, and the depth of the mixed surface layer
which varies over the globe.
Combining all three factors—melting of ice caps, receding of glaciers, and thermal expansion
of water—it is estimated that by the end of the twenty-first century the average sea level may be
30-50 cm higher than it is today. This can seriously affect low-lying coastal areas, such as the
Netherlands in Europe, Bangladesh in Asia, and low-lying islands in the Pacific and other oceans.
10.2.7.2 Climate Changes
Predicting global and regional climatic changes as a consequence of average surface temperature
rise is extremely difficult and fraught with uncertainties. It is expected that regional temperatures,
prevailing winds, and storm and precipitation patterns will change, but where and when, and to what
extent changes will occur, is a subject of intensive investigation and modeling on the largest available
computers, the so-called supercomputers. Climate is influenced not only by surface temperature
changes, but also by biological and hydrological processes and by the response of ocean circulation,
which are all coupled to temperature changes.
It is expected that temperate climates will extend to higher latitudes, probably enabling the
cultivation of grain crops further toward the north than at present. But crops need water. On the
average, the global evaporation and precipitation balance will not change much, although at any
instant more water vapor (humidity) may be locked up in the atmosphere. However, precipitation
patterns may alter, and the amount of rainfall in any episode may be larger than it is now. Con-
sequently, the runoff (and soil erosion) may be enhanced, and areas of flooded watersheds may
increase.
Hurricanes and typhoons spawn in waters that are warmer than 27
◦
C, in a band from 5
◦
to 20
◦
north and south latitude. As the surface waters will become warmer and the latitude band expands,
it is very likely that the frequency and intensity of tropical storms will increase.
The well-known ocean currents, such as the Gulf Stream, Equatorial, Labrador, Peru, and
Kuroshoi currents, are driven by surface winds and density differences in the water. A typical ex-
ample is the El Ni no event. Along the coast of Peru and Chile, prevailing winds blow offshore, driv-
ing the surface waters westward from the South American coast. This sets up a three-dimensional
pattern of ocean circulation in which the warm surface waters are replaced by upwelling of colder
water from depths reaching to 300 m. These colder waters are rich in nutrients on which pelagic
(water column) fish and other aquatic organisms feed—for example, the anchovies. This event
