The concentration of carbon dioxide in the atmosphere will persist above 400 parts per million, researchers have predicted. Using emissions data, sea surface temperature (SST) data, and a climate model, researchers at the U.K. Met Office have projected atmospheric CO2 concentrations through the end of 2016, finding that this will be the first year on record in which concentrations will be over 400 ppm for the full year at the Mauna Loa Observatory on Hawaii, according to a study published Monday in the journal Nature Climate Change.
“2014 was the first year that monthly CO2 concentrations rose above 400 ppm, and in 2015 the annual mean concentration has passed 400 ppm for the first time, but the monthly mean concentration fell back below 400 ppm for three months at the end of the boreal summer, reaching a monthly mean of 397.50 ppm in September,” according to the study.
If the scientists’ modeling is correct, there is only a remote possibility that mean concentration could drop below 400 ppm in 2016. “Assuming stationarity in the distribution of daily values around the monthly mean, the lowest daily CO2 concentration at Mauna Loa could be between 399.45 and 401.05 ppm. Therefore the daily values will be most likely to stay above 400 ppm,” the study says.
According to the study, there is nothing “physically significant” about the 400 ppm threshold, but it has become a large part of the conversation surrounding the ongoing rise in atmospheric CO2.
