Scientists at the Mauna Loa Observatory in Hawaii announced in 2013 that atmospheric concentrations of carbon dioxide reached a daily average above 400 parts per million for the first time in history. air pollution-014CO2 concentrations “haven’t been this high in millions of years,” said scientist Erika Podest at the time. “This milestone is a wake-up call.”  But the situation has only gotten worse. Worldwide, 400 ppm, which indicates the ratio of carbon dioxide to other gases in the atmosphere, started to be read more consistently and in more locations. Last March, global CO2 levels topped the symbolic benchmark for an entire month — a first since record-keeping began. Antarctica, the last place on Earth without a 400 ppm reading, finally reached it in May.  Now scientists say we’ve arrived at yet another critical climate change juncture: CO2 levels surpassed 400 ppm this month— and it may not fall below that mark ever again.  “I think we’re essentially over for good,” said Ralph Keeling, director of the Scripps Institute for Oceanography’s carbon dioxide monitoring program in May.  Keeling explained in a Friday blog post how CO2 levels had consistently topped 400 ppm for the month of September ― typically the time of year when atmospheric carbon dioxide is at its lowest. The Scripps Institute monitors CO2 levels at the Mauna Loa Observatory, the world’s marquee site for carbon dioxide monitoring.  “The low point reflects the transition between summer and fall, when the uptake of CO2 by vegetation weakens and is overtaken by the release of CO2 from soils,” he wrote. “Is it possible that October 2016 will yield a lower monthly value than September and dip below 400 ppm? Almost impossible.”  Though one-off lower measurements could still be read in the coming weeks, Keeling said “it already seems safe to conclude that we won’t be seeing a monthly value below 400 ppm this year, or ever again for the indefinite future.”  And since carbon dioxide stays in the atmosphere for hundreds, sometimes thousands of years, even the most rigorous climate action won’t dampen this figure. Not this century, anyway.  If CO2 emissions, for example, somehow plummeted to zero tomorrow, carbon dioxide levels “probably wouldn’t change much, but would start to fall off in a decade or so,” Gavin Schmidt, NASA’s chief climate scientist, told Climate Central. “In my opinion, we won’t ever see a month below 400 ppm.”

From Huff Post & Climate Central  Photo Credit John Vlahakis