The goal of limiting global temperature rise to 2 degrees Celsius (3.6 degrees Fahrenheit) by the end of this century was first agreed to in Copenhagen and then by all countries at the Cancun Climate Conference in 2010. It recognizes that climate change is already occurring, but that if we act now, we can avoid the worst impacts of a changing climate.
The Intergovernmental Panel on Climate Change has provided different scenarios regarding different levels of action. If nothing is done, and the world proceeds on its present course, world is on track for an average global-temperature rise of four degrees Celsius (more than seven degrees Fahrenheit) by the end of this century.
Owing to the carbon emissions that have been pumped into the air so far, average global temperatures have risen by about 0.85 degrees Celsius (1.5 degrees Fahrenheit). This relatively small increase has produced large effects: almost half of the permanent Arctic ice cap has melted away, millions of acres’ worth of trees in the American West have died from warming-related pest infestations, and some of West Antarctica’s major glaciers, containing tens of thousands of cubic miles of ice, have started to disintegrate. Even if CO2 levels were to stop rising tomorrow the world would continue to warm, by about .5 degrees Celsius (.9 degrees Fahrenheit).