20th CENTURY CLIMATE CHANGE

20th CENTURY CLIMATE CHANGE

Variations in land- and sea-ice coverage and the melting or growth of glaciers occur in response to changes in temperature, sunshine, precipitation, and for sea-ice changes in wind. Since 1966 Northern Hemisphere snow cover maps have been produced by the United States using satellite imagery. Consistent with the surface and tropospheric temperature measurements is the decrease (by about 10%) in snow cover and extent since the late 1960s. There has been a widespread retreat of mountain glaciers in non-polar regions during the 20th century. Variations in sea-ice extent have also been reported, with spring and summer sea-ice extent in the Northern Hemisphere decreasing by between 10 an 15% since the 1950s. Considerable interest is now focusing on Antarctica, where regional warming, as predicted has been more rapid than global warming as a whole. In recent years the summertime disintegration of the Larsen Sea Ice Shelf adjacent the Antarctic continent has been occurring on an unprecedented scale. In view of the rapidity at which it is taking place, such an event has been viewed as a possible signal of global warming.

Measurements of surface recorded around the world during the last 150 years indicate that global temperatures are now higher than in any decade over this period. During the 20^th century a global average surface temperature increase of about 0.6°C years has taken place, although the warming trend has not been smooth and has taken place rather differently between the Northern and Southern Hemispheres. With this in mind, it is important to recognise that global average surface temperature, as a measure of the global climate, represents an over-simplification. Winter temperatures and night-time minimums for example, may have risen more than summer temperatures and daytime maximums.



CLIMATE CHANGE

CLIMATE CHANGE

Although most scientists agree that global warming is the result of the enhanced greenhouse effect, natural processes can also upset the global energy balance in this way, causing similar rises in global temperature. A change in the amount of energy received by the Sun for example has often been proposed as the cause of global warming. The challenge facing scientists is to establish beyond doubt a between global warming and man-made greenhouse gas pollution.

Although we are currently concerned about global warming caused by mankind's of the natural through pollution, the Earth's climate has fluctuated many times in the past in response to natural mechanisms of climate change. Such changes in global climate have also occurred over much longer time scales, from hundreds and thousands of years to millions and hundreds of millions of years. In fact the current global warming trend which began at the end of the 19^th century spans only a tiny fraction of the Earth's climatic history. Taking a longer perspective on climate variability can help us gain a better understanding of the global climate and of the evolution of the climate today and in the future



ENCHANGED GREEN HOUSE EFFECT

ENCHANGED GREEN  HOUSE EFFECT

A greenhouse is built of any material that passes sunlight, usually glass, or plastic. It mainly heats up because the Sun warms the ground inside, which then warms the air in the greenhouse.

 The air continues to heat because it is confined within the greenhouse, unlike the environment outside the greenhouse where warm air near the surface rises and mixes with cooler air aloft.

This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature will drop considerably. It has also been demonstrated experimentally (1909) that a "greenhouse" with a cover of rock salt (which is transparent to infra red) heats up an enclosure similarly to one with a glass cover. named by analogy to greenhouses but this is a misnomer.

The greenhouse effect and a real greenhouse are similar in that they both limit the rate of thermal energy flowing out of the system, but the mechanisms by which heat is retained are different. A greenhouse works primarily by preventing absorbed heat from leaving the structure through i.e. ransport. The greenhouse effect heats the earth because greenhouse gases absorb outgoing radiative energy and re-emit some of it back towards earth.



INDUSTRIAL REVOLUTION

INDUSTRIAL REVOLUTION

The earliest beginnings of industrialisation can be traced to the development of the cotton industry in England in the first half of the 18^th century. Cotton was imported from the United States to Liverpool and transported to Manchester and other Lancashire towns, where the first cotton mills were built. Rapid growth in industrialisation began in the late 18^th century, the period often considered as the start of the Industrial Revolution.

By the beginning of the 19^th century, inventions were not just limited to the cotton industry. Steam engines were invented, providing a faster mode of transportation, instead of the use of horses and carriages. Steams engines and other machinery, of course, required coal as a fuel source, releasing the first emissions of and other gases which led to declining air quality in many cities.

The transition from a worker-based cottage industry a to machine-based economy, with the growth of factories and mass production, is traditionally known as the Industrial Revolution, which began in England and brought about the most fundamental changes to society since the development of agriculture thousands of years earlier

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Accompanying the Industrial Revolution was a massive growth in energy consumption, largely through the burning of coal, a. The Industrial Revolution marked the beginning of the period during which mankind began substantially altering the composition of the atmosphere.



HUMAN HEALTH

HUMAN HEALTH

Poorer communities will be more vulnerable than richer ones. However, richer countries will also be increasingly vulnerable as their populations age. Health risks can be addressed through various adaptation strategies. Adaptive options to minimise health impacts may include improved and extended medical care services, better housing and air conditioning, water purification and public education. The lack of resources will be a constraint in many regions, but negative health effects can be minimised through a transfer of technological, educational and medical expertise from the more developed nations to the less developed nations.

A significant indirect effect arising from global warming will be an increase in the range of vector-borne diseases such as malaria. Malarial mosquitoes may spread to higher latitudes and higher altitudes, taking advantage of the warmer Approximately 45% of the world's population presently live in the climate zone where mosquitoes transmit malaria. predict that this will increase to about 60% by the second half of, with maybe 80 million extra cases of malaria occurring each year. Increases in food- and water-related infections could also occur, particularly in tropical and subtropical regions. Warmer temperatures, reduced, and proliferating micro-organisms would lead to a higher incidence of diarrhoea, cholera, salmonellosis, and other such infections. Local reductions in could increase malnutrition and hunger, with long-term health consequences, particularly for children.



CARBON DIOXIDE

CARBON DIOXIDE

Carbon dioxide released by mankind into the atmosphere today will influence its atmospheric n the years to come, since the time taken for carbon dioxide to adjust to changes in sources or sinks is in the order of 50 to 200 years.

 The Intergovernmental Panel of Climate Change science experts, has estimated that to just stabilise concentrations at present day levels would require a massive 60% reduction of global carbon dioxide. In addition, because of the rather slow response of the global climate, even if we took action today to limit carbon dioxide emissions, mankind has already been committed to a certain amount of climate change over the next 50 years. The challenge for future generations will be to prevent further global climate change from taking place.

hrough Earth history the amount of carbon dioxide in the atmosphere has varied significantly.

The Earth's early atmosphere was probably composed mostly of carbon dioxide. At that time, the would have been very strong, trapping much more heat than today, but billions of years ago the Sun was not as hot. During the last few hundred million years, the concentration of atmospheric carbon dioxide has generally been declining. In the most recent geological past it has been only a trace gas making up a few hundred parts per million of the gases in the atmosphere.



DOING OUR BIT FOR GLOBALWARMING

DOING OUR BIT FOR GLOBALWARMING

Transport is the fastest growing energy-consumption sector in the world. Cars account for about 20% of worldwide man-made emissions. The average car user is responsible each year for a weight of carbon dioxide roughly equivalent to the weight of the car. Individual car use can be reduced by choosing alternative modes of travel, including public transport, walking and cycling.

Everyone contributes to global of, but it is not only governments which can take action to reduce the threat of global warming. We all use energy for heating our homes, running electrical appliances, cooking food and driving our cars. Most of this energy comes from the burning of, such as oil, coal and gas, which release, the main greenhouse gas, into the atmosphere. Despite uncertainties, the general scientific consensus is that increased levels of greenhouse gases as a result of mankind's activities are the Earth's natural and causing global warming. Energy use is responsible for about 75% of man-made carbon dioxide emissions. Therefore, it is important to try to reduce our dependence on fossil fuels and reduce energy consumption.

Energy used in the home can be saved by a number of measures, including draught proofing, insulation, and using energy efficient lighting and other household appliances. Although some energy-saving ideas may involve a substantial initial expense, in the long run the reduction in energy consumption saves money through reduced fuel bills.