"Global warming,"  occurs when the blanket of greenhouse gasses (GHGs) gets thicker. Climate models from UN’s Intergovernmental Panel on Climate Change, as well as models from other scientific bodies, indicate that global concentrations of GHGs have been rising steadily over the past 100 years.

As atmospheric concentrations of GHGs increase, the greenhouse blanket gets thicker. This causes heat to be trapped in the lower layers of the atmosphere and may cause global average temperatures to rise. Human activity -- particularly the burning of fossil fuels -- has made the blanket of greenhouse gases around the earth "thicker." The resulting increase in global temperatures is alterating the complex web of systems that allow life to thrive on earth, such as cloud cover, rainfall, wind patterns, ocean currents, and the distribution of plant and animal species.

The increase in GHGs is happening at unprecedented speed. If emissions continue to grow at current rates, it is almost certain that atmospheric levels of carbon dioxide will double from pre-industrial levels during the 21st century. It is possible they will triple. The UN’s IPCC assesses with very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming. The ‘best case’ computer climate models estimate that the average global temperature will rise by 1.8° C to 4.0° C by the year 2100. A temperature increase of 0.4° C occurred last century and for the next two decades, a warming of about 0.2° C per decade is projected should greenhouse gas emissions continue to rise at their current pace and are allowed to double from their pre-industrial level.

Source: Chicago Climate Exchange, UNFCCC, TreeFarms

The Greenhouse Effect and the Carbon Cycle

A “thicker” blanket of greenhouse gases traps more infrared radition and raises temperatures.

Source: UNFCCC