CO2 concentrations consign sub 400ppm level to history
Atmospheric concentrations of CO2 are not expected to drop below the historic milestone of 400 parts per million (ppm) this year nor possibly in our lifetime, by relying solely on natural processes, according to Nature Climate Change. A Yale study suggests that El Nino has pushed up and will keep levels elevated this year, but also points out that longer term, the concentration of CO2 in the atmosphere has risen roughly 48% since the pre-industrial era and 29% since 1958, accelerated by the burning of fossil fuels.

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 summer and increasing during winter. But in the study published in Nature, scientists at the U.K.’s Met Office and 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.