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The greenhouse effect is a vital natural phenomenon, intensified by human activity. The greenhouse effect happens when certain gases—known as greenhouse gases—collect in Earth’s atmosphere. These gases include carbon dioxide (CO2), methane, nitrous oxide (N2O), fluorinated gases, and ozone.

Greenhouse gases let the sun’s light shine onto the Earth’s surface, but they trap the heat that reflects back up into the atmosphere. In this way, they act like the glass walls of a greenhouse. This greenhouse effect keeps the Earth warm enough to sustain life. Scientists say that without the greenhouse effect, the average temperature of the Earth would drop from 14˚C (57˚F) to as low as –18˚C (–0.4˚F).

Some greenhouse gases come from natural sources. Evaporation adds water vapor to the atmosphere. Animals and plants release carbon dioxide when they respire, or breathe. Methane is released naturally from some low-oxygen environments, such as swamps. Nitrous oxide is produced by certain processes in soil and water. Volcanoes—both on land and under the ocean—release greenhouse gases, so periods of high volcanic activity tend to be warmer. 

Since the Industrial Revolution of the late 1700s and early 1800s, people have been releasing large quantities of greenhouse gases into the atmosphere. That amount has skyrocketed in the past century. Greenhouse gas emissions increased 70 percent between 1970 and 2004. Emissions of CO2, the most important greenhouse gas, rose by about 80 percent during that time. The amount of CO2 in the atmosphere today far exceeds the natural range seen over the last 650,000 years.

Most of the CO2 that people put into the atmosphere comes from burning fossil fuels. Cars, trucks, trains, and planes all burn fossil fuels. Many electric power plants do, as well. Another way humans release CO2 into the atmosphere is by cutting down forests, because trees contain large amounts of carbon.

People add methane to the atmosphere through livestock farming, landfills, and fossil fuel production such as coal mining and natural gas processing. Nitrous oxide comes from agriculture and fossil fuel burning. Fluorinated gases include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). These gases are used in aerosol cans and refrigeration.

All of these human activities add greenhouse gases to the atmosphere. As the level of these gases rises, so does the temperature of the Earth. The rise in Earth’s average temperature contributed to by human activity is known as global warming.

Essay on Greenhouse Effects Speech
Earth is the only planet that we know of that has the right conditions to support life. Because of it's perfect distance from the sun, Earth has an average temperature of 60F, making it an ideal place for many types of life to thrive in. However, the temperature would not be so ideal if we did not have an atmosphere with certain gasses in it. Without the help of gasses such as carbon dioxide, water vapor, and others, the Earths climate would not be suitable for life. Energy from the sun heats the Earth, where that energy is then radiated back into space. These gasses trap the energy and make the climate on Earth hospitable. Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. Because of the increase of concentrations of these gasses, more energy is trapped within the Earths atmosphere, which is slowly increasing the average heat levels. Scientist

Greenhouse Effects Speech Essay
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