NOAA reports that carbon dioxide in the atmosphere rose 3.05 parts per million in 2015, the largest annual increase recorded at the Mauna Loa Observatory since it began in 1957. Last year was the fourth consecutive year that CO2 concentrations grew by more than 2 parts per million. More recently, the change in average CO2 concentration from February 2015 till last month shows an even higher increase – 3.76 parts per million – bringing the current total concentration to 404.02 parts per million. To put these numbers in perspective, pre-industrial levels of carbon dioxide were 280 parts per million and when Mauna Loa started mid-20th century, they were below 320 parts per million. CO2 levels have increased over 40% since the beginning of the industrial revolution.
Scientists attribute some portion of this annual spike to the 2015 El Niño, because this weather pattern leads to tropical droughts that then produce wildfires ( e.g. Indonesia in 2015). Drought also limits forest growth, which decreases the number and size of trees that remove carbon dioxide from the atmosphere. These impacts are temporary as the forests bounce back in normal, non-El Niño years.
But Ralph Keeling of the Scripps Institution of Oceanography (and son of Charles Keeling, who founded the Mauna Loa program) warns that “the eventual recovery from this El won’t bring us back below 400 ppm, because its impact will be dwarfed by the global consumption of fossil fuels, pushing CO2 levels ever higher.”