Levels of carbon dioxide in the atmosphere are set to be above a symbolic threshold all year round for the first time in 2016, scientists have said.
Record annual rises in carbon dioxide levels, helped by a strong natural climate phenomenon known as El Nino affecting global temperatures and weather, will see concentrations of the greenhouse gas exceed 400 parts per million (ppm) all year.
The impacts of El Nino, such as dry conditions in the tropics which reduce the uptake of carbon and prompting forest fires that release the gas, are providing an “extra boost” on top of emissions from human activities such as burning fossil fuels.
Researchers writing in the journal Nature Climate Change forecast the rise in carbon dioxide in the atmosphere to be a record 3.15 ppm between 2015 and 2016, well above the average increase of 2.1 ppm a year over the past 60 years.
While the annual average concentration of carbon dioxide in the atmosphere passed the 400 ppm milestone in 2015, this year will be the first in which it will stay above that level for the whole year — and for our lifetimes, the scientists said.
The figures are based on the Mauna Loa carbon dioxide record in Hawaii in the US, which was started by Charles David Keeling in 1958 when early measurements were about 315 ppm in the atmosphere.
The paper’s lead author, Richard Betts, from the Met Office Hadley Centre and University of Exeter, said: “The atmospheric carbon dioxide concentration is rising year-on-year due to human emissions, but this year it is getting an extra boost due to the recent El Nino event.”
Fluctuations
Carbon dioxide (CO2) concentrations fluctuate slightly during the year, as plants draw down carbon dioxide in the northern hemisphere in the summer and release it in the autumn and winter.
Prof Betts said: “Carbon dioxide at Mauna Loa is currently above 400 parts per million, but would have been expected to drop back down below this level in September.
“However, we predict this will not happen now because the recent El Nino has warmed and dried tropical ecosystems and driven forest fires, adding to the CO2 rise.”
Emissions caused by humans are 25 per cent higher than during the last big El Nino event in 1997/1998, he said, adding up to a record rise in carbon dioxide levels in the atmosphere.
Prof Ralph Keeling, of the Scripps Institution of Oceanography, which measures carbon dioxide at Mauna Loa, said: “Back in September last year, we suspected that we were measuring CO2 concentrations below 400 ppm for the last time.
“Now it is looking like this was indeed the case.”
The average concentration in 2016 is forecast to be 404.45 ppm, dropping to 401.48 ppm in September before continuing with an onward rise next year, the researchers said.
PA