Global warming in the simplest form is when the earth heats up. The earth heats up when greenhouse gases such as carbon dioxide, water vapor, nitrous oxide, and methane traps heat and light from the sun ("Thinkquest"). With ample amount of gases in the air, the earth’s temperature rising will cause many of our animals and plants to die because they cannot sustain the heat ("Thinkquest"). Carbon dioxide concentration has increased due to the use of fossil fuel in electricity generation, transportation, industrial, and household goods. The concentration of carbon dioxide in the atmosphere has roughly by 35 percent since the start of the industrial revolution ("Global Climate). Water vapor is the most abundant greenhouse gas in the atmosphere. A warmer climate increases evaporation and allows more moisture to be held in the atmosphere which leads to more warming. With the more burning of more fossil fuel and fertilizer nitrous oxide amounts are increasing in the atmosphere ("Global Climate"). Methane concentration has increased as a result of agriculture. Livestock produce methane in their digestive tracts. About 70 percent of the emissions of atmospheric methane are now related to human activities ("Global Climate"). Human activities have increased the ozone concentration through the releases of the other greenhouse gases Excess ozone in the troposphere causes respiratory illnesses and other human health problems ("Global Climate"). The greenhouse effect is described when certain gases are trap heat in the earth’s atmosphere. Like the glass walls of a greenhouse, the gases let in light, but keep it from escaping. Many reports have led to the conclusion that humans have caused most or all of the warming. Industrialization, deforestation, and pollution have greatly increased atmospheric concentrations of water vapor, carbon dioxide, methane, and nitrous oxide, which all help trap heat near Earth's surface (Linsley). The earth temperature has increased to about 1.4° F over the course of three decades. Climate projections were summarized in the 2007 Fourth Assessment Report by the Intergovernmental Panel on Climate Change. They indicated that during the 21st century the global surface temperature is likely to rise a further 2 to 5.2 °F for their lowest emissions scenario and 4.3 to 11.5 °F for their highest ("Natural Wildlife Federation "). There is no doubt that global warming has a direct on impact where we will live, what food we can grow, where we can grow food, and where the animals live. Global warming is making hot days hotter, rainfall and flooding heavier, storms stronger, and droughts more severe. These changes are the most visible signs that global warming is showing us. With the Earth becoming a warmer place, its causing an effect on the