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The global warming hypothesis originated in 1896 when Svante Arrhenius, a Swedish chemist, developed the theory that carbon dioxide emissions from the burning of fossil fuels would cause global temperatures to rise by trapping excess heat in the earth's atmosphere. Arrhenius understood that the earth's climate is heated by a process known as the greenhouse effect. While close to half the solar radiation reaching the earth's surface is reflected back into space, the remainder is absorbed by land masses and oceans, warming the earth's surface and atmosphere. This warming process radiates energy, most of which passes through the atmosphere and back into space. However, small concentrations of greenhouse gases like water vapor and carbon dioxide convert some of this energy to heat and either absorb it or reflect it back to the earth's surface. These heat-trapping gases work much like a greenhouse: Sunlight passes through, but a certain amount of radiated heat remains trapped.

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The greenhouse effect plays an essential role in preventing the planet from entering a perpetual ice age: Remove the greenhouse gases from the atmosphere and the earth's temperature would plummet by around 60 degrees Fahrenheit (F). However, scientists who have elaborated on Arrhenius's theory of global warming are concernced that increasing concentrations of greenhouse gases in the atmosphere are causing an unprecedented rise in global temperatures, with potentially harmful consequences for the environment and human health.

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In 1988, the United Nations Environment Program and the World Meteorological Organization established the Intergovernmental Panel on Climate Change (IPCC), comprising more than two thousand scientists responsible for studying global warming's potential impact on climate. According to the IPCC, the atmospheric concentration of carbon dioxide has increased by 31 percent, methane by 151 percent, and nitrous oxide by 17 percent since 1750. Over the twentieth century, the IPCC believes that global temperatures increased close to 0.5 degree Centigrade (C), the largest increase of any century during the past one thousand years. The 1990s, according to IPCC data, was the warmest decade recorded in the Northern Hemisphere since records were first taken in 1861, with 1998 the warmest year ever recorded.

Task: Writing the outline for part of an article.

In this task you need to choose three important paragraphs from your article and write an outline showing you understand the difference between the main and supporting points.