Human-caused carbon dioxide emissions were roughly flat in 2014, 2015 and 2016, but National Oceanic and Atmospheric Administration figures show that 2015 saw a rise in carbon in the air 3.03 parts per million, the largest since scientists started tracking emissions in Hawaii in 1959.
The findings in the journal Science are based on data from a carbon-tracking satellite launched in 2014 by the USA space agency, known as NASA's Orbiting Carbon Observatory-2 (OCO-2). The satellite can also measure solar-induced fluorescence, a proxy for photosynthesis, which provides valuable information about the biological processes that affect atmospheric CO2.
"The data reveal a striking change in the carbon cycle in the Northern Hemisphere across seasons, where in the spring there's a dramatic uptake of carbon by terrestrial plants", said one of the five papers in Science.
"But during the winter, the production of Carbon dioxide by plants is minimal, and the decomposition of plant fuels the production of Carbon dioxide when the temperatures heat up".
According to the researchers, this change is mainly explained by a decrease of precipitation in South America and an increase in temperatures in Africa, a phenomenon that is expected to worsen by the end of the century with global warming. "And this combined with the emissions continued from the combustion of coal and hydrocarbons over the China, Europe and the United States explains that the rate of seasonal Carbon dioxide to reach the highest levels in April in the northern hemisphere", stated the scientists.
As the world warms, the tropics could add to carbon to the atmosphere in the future instead of taking it out of the air and wildfire emissions are likely to get more severe, Overpeck said.
The 2015 El Nino "resulted in the release of about 2.5 gigatons more carbon into the atmosphere in 2015 than in 2011", said the report.
In tropical Asia, the seasonal increase in Carbon dioxide emissions is explained mostly by the combustion of bio-mass.
During that same time, in Africa, rainfall was normal but temperatures were higher than usual.