Emissions scenarios , estimates of changes in future emission levels of greenhouse gases, have been projected that depend upon uncertain economic, sociological , technological , and natural developments.  In most scenarios, emissions continue to rise over the century, while in a few, emissions are reduced.   Fossil fuel reserves are abundant, and will not limit carbon emissions in the 21st century.  Emission scenarios, combined with modelling of the carbon cycle , have been used to produce estimates of how atmospheric concentrations of greenhouse gases might change in the future. Using the six IPCC SRES "marker" scenarios, models suggest that by the year 2100, the atmospheric concentration of CO 2 could range between 541 and 970 ppm.  This is 90–250% above the concentration in the year 1750.
9. Global Warming Effect: Widespread extinction of species
The above text about effects of global warming has been originally taken from and then adapted accordingly.
In order to understand the effects of all the gases together, scientists tend to talk about all greenhouse gases in terms of the equivalent amount of CO 2 . Since 1990, yearly emissions have gone up by about 6 billion metric tons of "carbon dioxide equivalent" worldwide, more than a 20 percent increase.
 Gore, Al, An Inconvenient Truth; The Planetary Emergency of Global Warming and What We Can Do About It, Rodale, Emmaus PA, 2006,
Thawing permafrost alters local ecosystems, destabilizes infrastructure and releases heat-trapping gases into the atmosphere, which spurs more climate change. Read how increasing ground temperatures worsen global warming .
Global warming is the term used to describe a gradual increase in the average temperature of the Earth's atmosphere and its oceans, a change that is believed to be permanently changing the Earth’s climate. There is great debate among many people, and sometimes in the news, on whether global warming is real (some call it a hoax). But climate scientists looking at the data and facts agree the planet is warming. While many view the effects of global warming to be more substantial and more rapidly occurring than others do, the scientific consensus on climatic changes related to global warming is that the average temperature of the Earth has risen between and °C over the past 100 years. The increased volumes of carbon dioxide and other greenhouse gases released by the burning of fossil fuels, land clearing, agriculture, and other human activities, are believed to be the primary sources of the global warming that has occurred over the past 50 years. Scientists from the Intergovernmental Panel on Climate carrying out global warming research have recently predicted that average global temperatures could increase between and °C by the year 2100. Changes resulting from global warming may include rising sea levels due to the melting of the polar ice caps, as well as an increase in occurrence and severity of storms and other severe weather events.