Describe And Explain In Detail The Characteristics

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)