Last week, NASA scientists published their blockbuster findings of what they learned from the observations they obtained over the first two years of operation of the Orbital Carbon Observatory-2 (OCO-2) satellite.

Launched on 2 July 2014, OCO-2 has the ability to measure the concentration of carbon dioxide in the Earth's atmosphere at spatial resolution down to 1.3 kilometer by 2.25 kilometer rectangles, a significant improvement over the 50 by 50 kilometer squares that marked the limit that previous satellites were able to produce. With that level of detail, the satellite's instruments are better able to detect the emission of carbon dioxide from both natural sources and from human activities much closer to their points of origin, before they become more generally dispersed into the Earth's atmosphere.

The timing of the launch of the OCO-2 satellite was particularly fortuitous, because it came in time to capture the effect of the very strong El Niño anomaly of 2015-2016 upon the level of carbon dioxide that was added to the Earth's atmosphere during those years.

But more to the point, the satellite data was able to determine the amount and source of that additional carbon dioxide produced from natural sources. The following chart shows that almost all of that contribution came from the tropics, where a combination of higher temperatures and drought conditions led to less carbon dioxide being captured by plants in the Earth's equatorial belt.

NASA totaled up the numbers related to the 2015-2016 El Niño event:

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.

“These three tropical regions released 2.5 gigatons more carbon into the atmosphere than they did in 2011,” said Junjie Liu of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, 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. 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.” A gigaton is a billion tons.

In 2015 and 2016, OCO-2 recorded atmospheric carbon dioxide increases that were 50 percent larger than the 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 3 parts per million of carbon dioxide per year -- or 6.3 gigatons of carbon. In recent years, the average annual increase has been closer to 2 parts per million of carbon dioxide per year -- or 4 gigatons 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.

Doing the math, that additional 2.5 billion metric tons of carbon translates into an additional 1.17 parts per million of carbon dioxide being emitted into the Earth's atmosphere from natural sources during the period of the 2015-16 El Niño anomaly.

Having now isolated that natural contribution to the increase in the concentration of atmospheric carbon dioxide over that period of time, we can now subtract it out from the total to quantify the portion that might be attributable to human activities combined with what would be considered to be typical levels of CO2 generated from natural sources, which would be more directly comparable to the kind of readings that would be obtained in years where El Niño events are not a significant factor affecting atmospheric carbon dioxide concentration measurements.

That in turn can tell us something about the relative health of the Earth's global economy, since human activities are primarily responsible for the increase in the year over year change in the concentration of atmospheric carbon dioxide over time. In this case, after subtracting out the contribution of the 2015-2016 El Niño anomaly on those measurements, we find that the peak value that would have been reached during this time would have fallen below the peak reached in 2013 and would be about the same as the peak reached in 2014.

For the Earth's global economy, that suggests that economic growth was largely flat from 2015 through 2016, where we would expect a faster rate of increase in the year over year change in CO2 levels if the Earth's economy was growing on net during that time.

Ideally, we'd like to get a month-to-month breakdown of how much additional CO2 was produced from natural sources during the 2015-2016 El Niño event, which would let us drill down into greater detail for the global economic performance that was realized during those years. And with data from the OCO-2 satellite, that might just be possible, which would allow us to directly take natural anomalies like a very strong El Niño episode into account in near-real time, as we would be better able to isolate and separate those factors from the CO2 produced via human activities.

That in turn would transform our vision for using the changing level of carbon dioxide in the Earth's atmosphere from human activities as a near-real time indication of the performance of the world's entire economy into a hum-drum practical achievement.

At least as the changing level of carbon dioxide in the Earth's air continues to be largely in proportion to the scope of human activities.

References

Florian M. Schwandner, Michael R. Gunson, Charles E. Miller, Simon A. Carn, Annmarie Eldering, Thomas Krings, Kristal R. Verhulst, David S. Schimel, Hai M. Nguyen1, David Crisp, Christopher W. O’Dell, Gregory B. Osterman, Laura T. Iraci, James R. Podolske. Spaceborne detection of localized carbon dioxide sources. Science. Vol. 358, Issue 6360, eaam5782. DOI: 10.1126/science.aam5782. 13 October 2017. Accessed 13 October 2017.

National Oceanographic and Atmospheric Administration. Earth System Research Laboratory. Mauna Loa Observatory CO2 Data. [File Transfer Protocol Text File]. Updated 5 Octobedr 2017. Accessed 8 October 2017.