“Two thousand scientists, in a hundred countries, engaged in the most elaborate and well-organized scientific collaboration in the history of humanity, have long produced a consensus that we will face a series of terrible catastrophes unless we take action to prepare for and address the underlying causes of global warming.” (Al Gore). So, what exactly is global warming? Has this happened before? If so, what were the effects? Specifically, how will it affect the human population? Do humans cause it? These are just some of the questions we need to answer when studying global warming. Global warming is the increase in the average temperature of the air and oceans near the Earth's surface that has occurred since the mid-20th century and its anticipated perpetuation. . Global warming is caused when carbon dioxide and other temperature-trapping emissions are vented into the atmosphere and serve a blanket-like function, letting light in but retaining heat in our atmosphere that would otherwise dissipate, resulting in more of the temperature. This is known as the greenhouse effect as it is very similar to the function of glass walls in a greenhouse. The first thing that happens is that sunlight shines onto the Earth's surface, where it is absorbed and subsequently released into the atmosphere as heat. This is hindered by the previously mentioned “greenhouse” gases, some of this heat escapes and some remains trapped in the atmosphere; the more greenhouse gases in the atmosphere, the more heat will be trapped. The greenhouse effect in its natural form is a good thing, since without it the earth would be at zero degrees Fahrenheit, instead of the current fifty-seven degrees Fahrenheit. The problem...... at the center of the paper......." Wikipedia, the free encyclopedia. Web. 19 April 2011. "Frequently asked questions about global warming." NCDC: * National Climatic Data Center ( NCDC ) *. Web. April 19, 2011. "Interactive Global Warming, Global Warming Simulation, Climate Change Simulation - National Geographic Environmental Facts, Environmental Science, Global Warming, Natural Disasters, Ecosystems, Ecological Living - Web of National Geographic April 19, 2011. “Global Warming.” Wikipedia, the free encyclopedia April 19, 2011. "MIT Center for Global Change Science".. 2011. .