When scientists talk about global warming they are talking about the average rise in the Earth's atmospheric and ocean temperatures over the past 100 years.The progressive gradual rise of the Earth's average temperature is thought to be caused in part by increased concentrations of gasses like carbon dioxide in the atmosphere from human processes. The burning of fossil fuels for electricity and transportation releases gasses in the atmosphere which causes the greenhouse effect. The greenhouse effect is the normal process of solar reflection that warms the Earth's surface. As the layer of gasses increases in the atmosphere, more heat is reflected back to Earth causing the gradual warming. The actual warming of the Earth is more than 1°F over many decades.

If historical trends of greenhouse gas emissions continue, it will result in additional warming over the 21st century. Current projections point to a global increase of 2.0°F to 11.5°F by 2100. Over the last century, average global temperatures rose by more than 1°F and some regions warmed by as much as 4°F. This warming has environmental consequences such as, additional sea-level rise that will gradually inundate coastal areas and increase beach erosion and flooding from coastal storms, ocean acidification, changes in rain patterns, increased risk of droughts and floods, threats to wildlife and biodiversity, impacts to farming and food systems and a number of potential challenges for public health with the increased spread of diseases. The phrase 'climate change' is growing in preferred use to 'global warming' because it helps convey that there are other changes in addition to rising temperatures.

Additional Resources

http://www.epa.gov/climatechange/                                                                                    

http://www.pewclimate.org/global-warming-basics/about

http://www.noaa.gov/climate.html