|Climate change trends and scenarios|
|<< GLOBAL CONTEXT >>|
|The atmosphere is an environment important for
life on the lands and in the oceans, upon which the existence of entire mankind is
Anthropogenic effects on the physical and chemical properties of the atmosphere have the potential to affect the quality of life and even the very existence of certain life forms.
Weather and climate-related disasters result in high death tolls, a decline in production of food, pollution of waters and land surfaces, and the destruction of production capacity and infrastructure.
Now, it is possible to be more confident in stating that the global climate is subject to changes. The mean global near-surface temperature has increased over last century by 0,6±0,2°C.
The rate of temperature rise is approximately 0,15°C per decade. The range of diurnal temperatures decreases in many parts of the globe. On average, the minimum temperatures grow approximately twice as fast as the maximum (0,2°C against 0,1°C per decade). According to IPCC, the rate of global warming in the 20th century has been, apparently, the most significant over the recent times, and the 1990s have been the warmest for last millennium and even longer.
The amount of precipitation over the land has changed insignificantly: from 0,5% to 1 % per decade.
Nevertheless, in some areas of the globe, the number of intensive and extreme precipitation has increased. Drier weather during summer given the temperature rise has brought about more droughts.
The data received from many observations indicate that regional climate changes have already affected many physical and biological processes and systems. Examples of observed changes include reduction in glacier cover, thawing permafrost, changes in altitudes of vegetation extent, reduction of populations of some species of plants and animals, expansion of desertification processes.
During millions of years of existence, the Earth's global atmosphere has been subject to constant changes. Saturation by oxygen, and formation of the ozone layer limiting pernicious short-wave radiation of the sun, have created favourable conditions for the development of life and for the existence of the biosphere as a whole. Finally, the complex interaction of the hydrosphere, lithosphere and the atmosphere has resulted in the formation of the modern climate.
The key factors determining the development and status of the climate are solar radiation and its spatial and temporal changes, arrangement of water and land, height of the terrestrial surface and form of the relief. Secondary, but not less important factors, are the global circulation of the atmosphere and the anthropogenic impact on the climate.
An important element of the climatic equilibrium of the globe is the greenhouse effect, which maintains the atmosphere of the Earth in a status of thermal balance favorable for existence of animals and plants. Life and water on the Earth exist mainly thanks to the greenhouse effect; it heats the surface of the Earth by 33°C and maintains a mean near-surface temperature of the globe at the level of 15°C above zero. Without the greenhouse effect, the average temperature of the Earth's surface would be -18°C. Greenhouse effect is particularly noticeable at Venus, where the surface temperature is 420°C.
The most significant natural greenhouse gas, due to its abundance, is water vapor. The next most greenhouse gas - CO2 occurs in the atmosphere naturally and as a result of anthropogenic emissions. Less significant greenhouse gases include nitrous oxide (N2O), methane (CH4) and others. Their molecules absorb and re-emit reflected long-wave radiation bearing free heat, and prevent it from dispersion in space. As a result, there is an increase in the surface temperature of the globe.
The direct interrelation between the change in the atmospheric concentration of CO2 and surface temperature of the globe has been proved through research conducted on glacier cover of the Antarctic Region.
To estimate the future climate of the Earth and to study the history of the global climate, world research centers developed climatic models. Modern models take into account the atmospheric concentration of greenhouse gases and aerosols, chemical processes in the atmosphere, the complex interaction between land, atmosphere, ocean and sea ice, circulation of carbon in the environment, the dynamics of the vegetative cover and others.
According to the estimations of IPCC, the increase in the global mean temperature by 2100 could range from 2,5-5,0°C or higher, particularly in the polar areas of the globe and tropics. Some uncertainties arise regarding how warming, in connection with growing evaporation and condensation of water, will affect cloud formations and what this impact will be on the climatic system.
At first glance, warming seems to be moderate. However, such a prompt rise in temperature could be disastrous. Moreover, such warming will cause the thawing of mountain glaciers and polar ice and the thermal expansion of the world's oceans, sufficient to cause a rise of 0,4-1,2 m in sea level.
This warming will also result in the flooding of extensive coastal zones and will increase the frequency of natural disasters and their resultant damage.
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