Реферат: Global warming
«Global warming» has been introduced by the scientificcommunity and the media as the term that encompasses all potential changes inclimate that result from higher average global temperatures. Hundreds ofscientists from many different countries are working to understand globalwarming and have come to a consensus on several important aspects. In general,Global warming will produce far more profound climatic changes than simply arise in global temperature.
An analysis of temperature records shows that the Earth has warmedan average of 0.5°C over the past 100 years. This is consistent withpredictions of global warming due to an enhanced greenhouse effect andincreased aerosols. Part of the current global warmth is associated with thetropical El Nino, without which a record global temperature would probably nothave occurred.
The Earth's climate is the result of extremely complex interactionsamong the atmosphere, the oceans, the land masses, and living organisms, whichare all warmed daily by the sun's energy. This heat would radiate back into spaceif not for the atmosphere, which relies on a delicate balance of heat-trappinggases — including water vapor, carbon dioxide, nitrous oxide, and methane — toact as a natural «greenhouse,» keeping in just the right amount ofthe sun's energy to support life.
For the past 150 years, though, the atmospheric concentrations ofthese gases, particularly carbon dioxide, have been rising. As a result, moreheat is being trapped than previously, which in turn is causing the globaltemperature to rise. Climate scientists have linked the increased levels ofheat-trapping gases in the atmosphere to human activities, in particular theburning of fossil fuels (coal, oil, and natural gas for heating andelectricity; gasoline for transportation), deforestation, cattle ranching, andrice farming.
As the Earth's climate is the result of extremely complexinteractions, scientists still cannot predict the exact impact on the earth'sclimate of these rising levels of heat-trapping gases over the next century.The current best estimate is that if carbon dioxide concentrations double overpreindustrial levels, according to the scientific possible scenarios, anatmospheric doubling of carbon dioxide could occur as early as 2050.
In 1995, scientists with the Intergovernmental Panel on ClimateChange — the authoritative international body charged with studying thisissue-reached a conclusion in the Second Assessment Report, which summarizesthe current state of scientific knowledge on global warming, also calledclimate change.
For the first time ever, the Panel concluded that the observedincrease in global average temperature over the last century «is unlikelyto be entirely natural in origin» and that «the balance of evidencesuggests that there is a discernible human influence on global climate.»
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