Of The Urban Heat Island. Essay, Research Paper
Humans have adjusted agricultural
and other activities to the current climatic configuration of the Earth.
Climatic conditions, however, change with time, as, for example, from the
apparent warm, humid global conditions of the Carboniferous Period to the
widespread continental glaciations of the Pleistocene Epoch. Using fossils and
other geologic evidence (e.g., Erosional landforms, shoreline features, and
glacial deposits), paleoclimatologists have demonstrated that the periodic
occurrence of extensive glaciations separated by long periods of a warm global
climate is a recurrent characteristic of the Earth. The causes of these
climatic changes have been attributed to a variety of mechanisms, including
increased volcanic emissions that have been associated with the blocking of
sunlight and the resultant cooling at the surface. Periodic reductions in solar
output also have been suggested as the cause of global cooling. The movement of the continents
over the Earth’s surface over long time periods is thought to have caused
different global climatic patterns. This migration of the landmasses, known as
continental drift, has been invoked to explain geologic evidence of tropical
fauna in Antarctic and of glaciers at low altitudes in Africa. Variations over time of the
obliquity of the Earth’s axis with respect to its orbital plane, the
eccentricity of the orbit, and the precession of the axis directly influence the
distribution of solar radiation over the planet and therefore the climate. The
obliquity of the Earth varies between 24° 36′ and 21°39′ from its current value
of 23°30′ over a period of approximately 40,000 years. The eccentricity ranges
between about 0 to 0.05 from its current value of 0.016 over a time period of
about 92,000 years, while the precession of the axis requires from 16,000 to
26,000 years to make a complete circle. The most pronounced difference between
winter and summer seasons occurs with a large obliquity And a large eccentricity such that winter occurs when the
Earth is farthest from the Sun. Over the last few hundred years,
humankind has been directly influencing global and local climate. The
development of urban areas has created different ground characteristics that
have resulted in urban heat islands in which cities are warmer, particularly at
night, than the surrounding countryside. This is because there are more tower
blocks to cast shadows and there are many non-reflective building materials
that are used in the construction of urban areas and so they absorb heat rather
than reflect it. This is due to the fact that there are dark coloured roads and
walls so they can absorb heat and store it and release it slowly later on so
the towns hold heat for longer further heat is gained from car fumes,
factories, power stations, central heating and people themselves. Urban heat
island is why large cities have less snow, frosts and earlier budding and
germination of plants and flowers and a greater need for air-conditioning than
places in the summer. The input of carbon dioxide (CO2) into the atmosphere
through industrial activities has been suggested to be associated with warming
near the surface as additional long-wave radiation emitted at the surface is
absorbed by the CO2 and radiated back toward the surface. In the period
1958-75, for example, the average CO2 level of the atmosphere increased at a
rate of about 1.7 parts per million per year. There is concern that by the year
2100 the enhanced CO2 level resulting from industrial activity will increase
the average global temperatures by as much as 5° C, with the greatest impact at
high altitudes. ?Aerosols are also released into the atmosphere by industrial and
other human activities. Climatologists have suggested that
anthropogenic-generated aerosols could alter the Earth’s radiation budget,
perhaps even counteracting the warming effect of CO2. The ability of additional
aerosols to heat or to cool the Earth’s atmosphere depends on their vertical
and horizontal distribution, and their concentration, size, and chemistry. The addition to the atmosphere of
anthropogenic aerosols, which serve as additional cloud condensation and ice
nuclei, also could alter the percentage of the Earth covered by clouds.
Increased concentrations of cloud condensation nuclei, for instance, would
reduce the average droplet size within a cloud, making the droplets more
colloidally stable and thus less likely to precipitate. Such clouds are likely
to persist longer, resulting in enhanced reflection of sunlight during the day
(i.e., a cooling effect) but a reduction of long-wave radiational cooling at
night if the clouds are in the low to middle troposphere. The net effect on the
global climate remains unclear.??????????????????????? Bibliography:??? Britannica encyclopaedia ??????????????????????????????????????????????? Encarta
encyclopaedia ??????????????????????????????????????????????? Geography,
an integrated approach (David Waugh)