WASHINGTON: The 2015-16 El Nino - one of the largest on record, caused the largest annual increases in atmospheric carbon dioxide concentration seen in at least 2,000 years, a NASA study has found.
Analysing the first 28 months of data from NASA Orbiting Carbon Observatory-2 (OCO-2) satellite, researchers concluded that the impacts of El Nino-related heat and drought occurring in tropical regions of South America, Africa and Indonesia were responsible for the record spike in global carbon dioxide.
El Nino refers to a band of warm ocean water that develops in the Pacific Ocean and causes global changes of both temperatures and rainfall.
Scientists suspected the 2015-16 El Nino - one of the largest on record - was responsible, but exactly how has been a subject of ongoing research.
"These three tropical regions released 2.5 gigatonnes more carbon into the atmosphere than they did in 2011," said Junjie Liu of NASA's Jet Propulsion Laboratory in the US, who is lead author of the study.
"Our analysis shows this extra carbon dioxide explains the difference in atmospheric carbon dioxide growth rates between 2011 and the peak years of 2015-16," said Liu.
"OCO-2 data allowed us to quantify how the net exchange of carbon between land and atmosphere in individual regions is affected during El Nino years," she said.
In 2015 and 2016, OCO-2 recorded atmospheric carbon dioxide increases that were 50 per cent larger than average increase seen in recent years preceding these observations.
These measurements are consistent with those made by the National Oceanic and Atmospheric Administration (NOAA).
That increase was about three parts per million of carbon dioxide per year - or 6.3 gigatonnes of carbon.
In recent years, the average annual increase has been closer to two parts per million of carbon dioxide per year - or four gigatonnes of carbon.
These record increases occurred even though emissions from human activities in 2015-16 are estimated to have remained roughly the same as they were prior to the El Nino, which is a cyclical warming pattern of ocean circulation in the central and eastern tropical Pacific Ocean that can affect weather worldwide.
Using OCO-2 data, the team analysed how Earth's land areas contributed to the record atmospheric carbon dioxide concentration increases.
They found the total amount of carbon released to the atmosphere from all land areas increased by three gigatonnes in 2015, due to the El Nino.
About 80 per cent of that amount - or 2.5 gigatonnes of carbon - came from natural processes occurring in tropical forests in South America, Africa and Indonesia, with each region contributing roughly the same amount.
"Understanding how the carbon cycle in these regions responded to El Nino will enable scientists to improve carbon cycle models, which should lead to improved predictions of how our planet may respond to similar conditions in the future," said OCO-2 Deputy Project Scientist Annmarie Eldering of JPL.
"The team's findings imply that if future climate brings more or longer droughts, as the last El Nino did, more carbon dioxide may remain in the atmosphere, leading to a tendency to further warm Earth," Eldering said.