Are atmospheric greenhouse gas concentrations changing to levels compatible with the 2 °C (and possibly 1.5 °C) Paris Agreement temperature targets?

Key messages

(26 Nov 2019)

• The annual average concentration of carbon dioxide (CO₂), the most significant anthropogenic greenhouse gas, increased to 405 and 408 parts per million (ppm) in 2017 and 2018, respectively.

• The total concentration of all greenhouse gases, including cooling aerosols, reached a value of 454 ppm in CO₂ equivalents in 2017 — an increase of more than 4 ppm compared with 2016, and 37 ppm more than 10 years ago. 
• If the concentrations of the different greenhouse gases continue to increase at current rates, peak concentration levels required to stay below a temperature increase of 1.5 °C  above pre-industrial levels could be reached within the next 3-13 years. Peak concentration levels required to stay below a maximum 2 °C temperature increase could be reached in 15-29 years. In both cases a 50 % probability of exceedance and no a temperature overshoot are assumed. 
• Given the increasing concentration levels, negative emissions may become important to increase the probability of remaining below the temperature objectives agreed in the 2015 Paris Agreement on the climate.

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