El Nino may boost CO2 levels to record high this year

Atmospheric carbon dioxide concentration is rising due to human emissions, but this year it is getting an extra boost due to the recent El Nino event

Atmospheric carbon dioxide levels will see a record rise this year, soaring to above 400 parts per million, as the climate phenomena of El Nino will give an extra boost to the concentration of the greenhouse gas, a new study predicts.

"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 - changes in the sea-surface temperature of the tropical Pacific Ocean," said Richard Betts, from the Met Office Hadley Centre for Climate Change and University of Exeter in the UK.

"This warms and dries tropical ecosystems, reducing their uptake of carbon, and exacerbating forest fires," said Betts.

"Since human emissions are now 25% greater than in the last big El Nino in 1997/98, this all adds up to a record carbon dioxide rise this year," he said.

Using a seasonal climate forecast model and statistical relationship with sea temperatures, researchers forecast the rise this year to be a record 3.15 parts per million.

The average concentration in 2016 is forecast to be about 404.45 parts per million, dropping to about 401.48 in September before resuming their ongoing rise next year.

The scientists successfully predicted this year's maximum concentration of 407 parts per million last month.

The CO2 measurements were taken at the Mauna Loa Observatory in Hawaii, which continuously monitors and collects data related to atmospheric change since the 1950s.

CO2 concentrations also show modest ups-and-downs with the seasons. Plants draw down CO2 in the summer and release it again in the autumn and winter.

"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," Betts said.

"However, we predict that 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," he said.

Since natural processes only remove CO2 from the atmosphere gradually, levels will remain high even if human emissions began to decline.

Scientists expect the concentrations to now remain above 400 parts per million for at least a human lifetime.

"Studying how these natural cycles interact with human influences is an important part of climate science. Making and testing predictions like this helps us build our understanding and further develop climate models," said Chris Jones, from the Met Office Hadley Centre.

The study was published in the journal Nature Climate Change.