Climate change is the most serious environmental challenge facing society in the 21st century. There is little doubt that human activities have modified the composition of the atmosphere: the concentration of carbon dioxide, produced mainly by burning fossil fuels, has increased more than 30% since pre-industrial times. Carbon dioxide is one of several greenhouse gases (GHGs) that trap energy emitted by the Earth to outer space; other GHGs also affected by human activities are methane and nitrous oxide. The average temperature of the Earth's surface is increasing, and the frequency of extreme weather events such as intense hurricanes, droughts and floods is also increasing. Furthermore, the International Panel on Climate Change has concluded that there is more than 90% probability that this modification in atmospheric composition is the cause of the observed changes in the Earth’s climate in recent decades.

The average temperature of the Earth’s surface has so far increased by about 0.8 degrees Celsius since the Industrial Revolution. The consensus of informed experts is that the risk of causing dangerous changes to the climate system increases rapidly if the average temperature rises three or more degrees. Society faces an enormous challenge to effectively reduce GHG emissions so that the average temperature does not increase above two or possibly two and a half degrees Celsius. This goal can only be achieved by taking simultaneously measures such as drastically increasing energy efficiency in the transportation, building, industrial and other sectors, using renewable energy sources such as wind, solar, geothermal and biomass, and even developing and using safer nuclear energy power plants. Fossil fuels such as coal and petroleum can continue to be used beyond a transition period as long as the emitted carbon dioxide is sequestered and stored in underground reservoirs such as saline domes.