Long Periods Of A Warm Global Climate example essay topic

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), paleo climatologists 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 24^0 36 and 21^039 from its current value of 23^030 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 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 (CO 2) 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 CO 2 and radiated back toward the surface. In the period 1958-75, for example, the average CO 2 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 CO 2 level resulting from industrial activity will increase the average global temperatures by as much as 5^0 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 CO 2. 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 colloid ally 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).