A Nasa satellite has provided remarkable new insights on how CO2 is moved through the Earth’s atmosphere. The Orbiting Carbon Observatory (OCO) tracked the behaviour of the gas in 2015/2016 – a period when the planet experienced a major El Nino event. This climate phenomenon boosts the amount of CO2 in the air.
The US space agency’s OCO satellite was able to show how that increase was controlled by the response of tropical forests to heat and drought. The forests’ ability to draw down carbon dioxide, some of it produced by human activity, was severely curtailed.
The science has significant implications because the kind of conditions associated with El Ninos are expected to become much more common under global warming.
"If future climate is more like this recent El Nino, the trouble is the Earth may actually lose some of the carbon removal services we get from these tropical forests, and then CO2 will increase even faster in the atmosphere," explained Scott Denning, an OCO science team member from Colorado State University in Fort Collins. That would amplify warming, he told reporters.
Technical papers describing OCO’s work have just been published in Science Magazine. El Ninos occur when warm waters in the western Pacific periodically shift eastwards. This sets off a global perturbation in weather systems, redistributing rainfall and bumping up temperatures.
The 2015/16 event was one of the strongest on record and this was evident in the rise of CO2.
Normally, the concentration of the gas in the atmosphere goes up each year by about two parts per million by volume (ppmv) of air molecules – the equivalent of four gigatonnes of extra CO2. The current total is just over 400ppmv.