A record jump in atmospheric carbon dioxide levels in 2015 hints at a shortening timeline to hold global warming below the long-term target of 1.5ºC above pre-industrial averages that negotiators adopted at the 2015 United Nations climate summit in Paris.
CO2 levels measured at the Mauna Loa Observatory in Hawaii showed an average annual increase of 3.05 parts per million during 2015, the highest on record. As well, “atmospheric carbon dioxide concentrations have spiked more in the period from February 2015 to February 2016 than in any other comparable period dating back to 1959,” the Washington Post reports, citing the U.S. National Oceanic and Atmospheric Administration.
Beyond the absolute jump over the past year, CO2 levels have now increased by more than 2 parts per million in each of the last four years. “We’ve never seen that,” said Pieter Tans, lead scientist at NOAA’s Global Greenhouse Gas Reference Network. “That’s unprecedented.”
The Earth last experienced such sustained CO2 rise during the end of the last glacial age, between 17,000 and 11,000 years ago. Greenhouse gas concentrations are now rising 200 times faster than they did then.
In November 2014, Carbon Brief calculated that the world had just 72 months of then-current emissions left in the global carbon budget that would give Earth’s climate a two-thirds chance of staying below the 1.5°C target. That timetable, already down to 56 months, may now need to be shortened again.