Global warming is the increase in the average temperature of the earth's surface (Mastrandrea n. pag.). According to scientists, man is the main cause of global warming. Scientists argue that global carbon dioxide emissions should be halved over the next fifty years, otherwise the effects could be irreversible (Eilperin n. pag.). The two main activities humans do to contribute to global warming are burning fossil fuels and clearing land. Most fossil fuels come from burning in cars, factories, and power plants that provide energy to homes and offices (McClure n. pag.). Continuing global warming can cause damage to plants and animals that live in the sea and force plants and animals on land to move to new habitats. It could also change weather patterns that cause floods, droughts and an increase in damaging storms. Global warming could melt the polar ice caps enough to raise sea levels, and in some parts of the world human diseases could spread and crop yields could decline (Mastrandea n. pag.). Additionally, during photosynthesis, the process trees and other plants use to produce food; they remove carbon dioxide from the atmosphere. Land clearing contributes to an increase in carbon dioxide by decreasing the rate at which it is removed from the atmosphere during photosynthesis. Some scientists argue that the increase in greenhouse gases does not have much impact on temperatures. Instead, they think natural processes may have caused global warming. Such processes include increasing the energy emitted by the sun. But most climate scientists believe that increased solar energy has contributed only slightly to global warming. (Mastrandea n. pag.). However, global war...... middle of paper ......ld Book, Inc.McClure, Robert and Lisa Stiffler. "Scientists agree: humans cause global warming." Seattle News, Sports, Events, Entertainment | Seattlepi.com - Seattle Post-Intelligencer. 02 February 2007. Web. 21 November 2010. .Shah, Anup. “Climate Change and Global Warming: Global Issues.” Global Issues: Social, political, economic and environmental issues that affect us all: Global issues. 27 September 2010. Web. 27 November 2010. United Nations Environment Program - World Meteorological Organization. "What human activities contribute to climate change? From common questions about climate change." What's new? 1997. Network. November 21. 2010. .