The Intergovernmental Panel on Climate Change (IPCC) was established by the United Nations and is universally recognized as the leading authority on the science of Climate Change. The most recent findings from the IPCC conclude that climate change is "unequivocal" and that human activity is the main cause.
The burning of fossil fuels to meet the demand for energy coupled with deforestation has caused the greenhouse gas (GHG) concentrations to shift out of balance. The primary and most talked about GHG is carbon dioxide. Methane, nitrous oxides, sulphur oxides and volatile organic compounds are also GHGs contributing to global warming.
The level of carbon dioxide (CO2) in the atmosphere has grown to 380 parts per million (ppm), a nearly 40-percent increase from pre-industrial levels. Concentrations of other GHG have also increased greatly.
Greenhouse gases work like a greenhouse, trapping heat from the earth that would otherwise escape. GHGs when in a natural balance with other gases make life on Earth possible. As the concentration of GHGs in the atmosphere increases, the ability for these gases to trap heat increases. Over the last century, the mean temperature on Earth has increased by 0.74C, in Canada the mean temperature has risen by over 1C. Eleven of the twelve warmest years on record have occurred since 1995.
The impacts of global warming are much more than just a mean temperature increase of a couple of degrees. With the rise in temperatures, glaciers around the world are melting and there has been a notable increase in the number of extreme weather events such as hurricanes, tornadoes, and flooding. The term "climate change" is now being used instead of the term "global warming".
High levels of greenhouse gases can also be associated with poor air quality.