Greenhouse gases (GHG) are those gases that absorb and emit infrared radiation. The primary greenhouse gases in the Earth’s atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone.
Atmospheric concentrations of greenhouse gases are the balance between sources of emissions (from human activities and natural systems) and sinks (removal from the atmosphere). Human activities since the beginning of the Industrial Revolution in 1870 have produced approximately a 40% increase in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 407 ppm in 2017. Carbon dioxide emissions produced by human activities are called anthropogenic emissions.
Estimates suggest that on the current emissions trajectory a threshold of 2 °C global warming could be passed by 2050. The United Nations’ IPCC has designated2 °C as the upper limit to avoid “dangerous” global warming.