How are atmospheric concentrations of greenhouse gases developing compared with levels consistent with limiting the increase in global mean temperature to 2 °C or even 1.5 °C above pre-industrial levels?

Key messages

(14 Dec 2017)

• Global average concentrations of various atmospheric greenhouse gases are continuing to increase.
• The annual average concentration of carbon dioxide (CO₂) — the most important greenhouse gas — increased to 400 and 403 parts per million (ppm) in 2015 and 2016, respectively. This represented an increase of about 45 % compared with pre-industrial levels.
• The total concentration of all greenhouse gases, including cooling aerosols, reached a value of 445 ppm in CO₂ equivalents in 2015 — an increase of nearly 4 ppm compared with 2014, and 35 ppm more than in 2005.
• The current total concentration of all greenhouse gases implies that the long-term probability of the global average temperature exceeding 1.5 °C above pre-industrial levels is already about 50 %. The atmospheric greenhouse gas concentration that would be consistent with limiting global mean temperature increase to less than 2 °C could be exceeded in the coming decades.
• This shows the urgency of changing the emission trend and reducing greenhouse gas emissions considerably.

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