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Global Warming
'Global warming' is a warming of the earth compared to annual average global temperature records that have been kept since the 1880s. Global warming is caused naturally by increasing solar radiation, natural cyclic changes of and outside the earth, but primarily by increasing greenhouse gas emissions from human activities, which has been steadily rising since about 1750. Carbon dioxide, methane and nitrous oxide seem to contribute the most to climate change such as global warming, while aerosols in the atmosphere deplete the ozone and produce cooling effects known as 'global dimming'. Cooling effects caused by aerosols however, are overcome by about twice the warming effects caused by greenhouse gases, which results in an overall warming of the planet.

As natural processes of and outside the earth, and human activities such as overpopulation, environmental pollution and overconsumption of natural resources increases the concentration of greenhouse gases within the atmosphere, the average temperature of the planet gets warmer. Some experts estimate that the earth's average global temperature has already increased by about 33° F since the beginning of this century, due to the increase in greenhouse gases. Some estimate that by the middle of the next century, the average global temperature of earth may be 34-37° F higher than it is today.

Climate Change

An abrupt change in weather patterns that persists for decades or longer is referred to as 'climate change', which effects the productivity, health, diversity, distribution and seasons of ecosystems. Climate change is caused by changes in solar radiation, natural cyclic changes within and outside the earth's atmosphere, but primarily by greenhouse gas emissions from human activities. As increasing greenhouse gases cause earth's climate to get warmer, its ecosystems are also altered. Ice and snow melts, global sea levels rise, C02 sinks and freshwater sources shrink. Ocean acidification, acid rain, eutrophication (low oxygen levels in the water) and low oxygen areas called 'ocean dead zones' continue to increase. Acid rain can harm plants and aquatic animals, while climate change, acid rain, ocean acidification, ocean dead zones, and overfishing are known to cause mass extinctions of marine species.

Global Cooling

According to the UN's Intergovernmental Panel on Climate Change (IPCC), humans have been the primary source of greenhouse gases and cause of global warming since 1950. The greenhouse effect is also predicted to continue increasing global temperatures, causing earth's climate to keep getting warmer. In time, this global warming effect could cause oceans to evaporate more water and thus increase precipitation, resulting in additional water vapors and clouds in the atmosphere. More clouds in the atmosphere could then reflect more solar radiation back to space, reducing the total amount of heat energy absorbed by the atmosphere and surface of earth, which can thereby counteract the greenhouse effect enough to result in an overall cooling, rather than a warming of the planet -- especially when combined with the cooling effects of ozone depletion.
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