Atmospheric concentrations of CO2 will stay permanently above 400 parts per million (ppm) this year due to El Nino—and will likely not drop below that number again “within our lifetimes,” according to a study published this week in the journal Nature. The milestone represents a symbolic threshold that scientists and environmentalists had long sought to avoid. Greenhouse gases have jumped 48 percent from the pre-industrial era, and 29 percent in just the past 60 years, from 315 ppm to 407 ppm today. CO2 concentrations tend to ebb and flow with the seasons, dipping as vegetation grows in the summer and increasing during the winter. The burning of fossil fuels has contributed to a steady increase in annual measurements. But in the study published in Nature, scientists at the U.K.’s Met Office and the University of California, San Diego warned that because of the recent El Nino, CO2 concentrations wouldn’t fall below 400 ppm this year, or any year into the distant future.
“Once you have passed that barrier, it takes a long time for CO2 to be removed from the atmosphere by natural processes,” climate scientist and lead author of the study Richard Betts told The Guardian. “Even if we cut emissions, we wouldn’t see concentrations coming down for a long time, so we have said goodbye to measurements below 400 ppm.”
The study is based on measurements taken at Mauna Loa Observatory in Hawaii. Scientists first began tracking daily CO2 levels at the site, which sits atop a volcano, in 1958. The resulting record, known as the Keeling Curve, is one considered a pillar of modern climate science.
This article was first published in Yale Environment 360