A new NASA study provides space-based evidence that Earth’s tropical regions were the cause of the largest annual increases in atmospheric carbon dioxide concentration seen in at least 2,000 years.
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.
Analyzing the first 28 months of data from NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite, researchers conclude 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.
The findings are published in the journal Science Friday as part of a collection of five research papers based on OCO-2 data.
In 2015 and 2016, OCO-2 recorded atmospheric carbon dioxide increases that were 50% larger than the average increase seen in recent years preceding these observations.
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.
South America, Africa and Indonesia released 2.5 gigatonnes (a billion tonnes) more carbon into the atmosphere than they did in 2011. In 2011, whether in the three tropical regions was normal and the amount of carbon absorbed and released by them was in balance.
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. These 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.
About El Nino:
El Nino, Spanish for ‘The little boy’, is a weather disturbance first noticed (and named) by fishermen off the coast of South America centuries ago.
Under normal weather conditions, trade winds ferry warm ocean currents westwards, from the eastern and central Pacific towards Indonesia and Australia. Warmer ocean waters in these regions then heat up the air above, leading to cloud formation and triggering the prodigious monsoon.
But in the years where the El Nino takes shape, eastern and central Pacific regions experience abnormal warming of the sea.
This leads to increased cloud formation and torrential rains in Peru and some sections of America. The ocean currents in the western Pacific remain cool, which means weak monsoon rains in Indonesia and Australia and sometimes in India.