ASSIMILATING SATELLITE DATA YIELDS A
FIRST LOOK AT COVID-19’S IMPACT ON CARBON DIOXIDE
Combining NASA satellite data with a computer model yields a first look at changes in global carbon dioxide (CO2) concentrations after Coronavirus Disease 2019 (COVID-19) restrictions began during early 2020.
Using a custom configuration of the NASA Center for Climate Simulation (NCCS) Discover supercomputer, a team of NASA Global Modeling and Assimilation Office (GMAO) and Jet Propulsion Laboratory (JPL) scientists and collaborators assimilated 6 years of data from NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite into the Goddard Earth Observing System (GEOS) model.
Separate studies led by Corinne Le Quéré of the University of East Anglia and Zhu Liu of Tsinghua University estimated CO2 emissions changes by analyzing activity data across different sectors, including residential, public, aviation, power, industry, and surface transportation. These studies suggest that global daily CO2 emissions decreases peaked at 15–20 percent in April and were down roughly 7 percent for the first four months of 2020.
Despite this information, it is difficult to observe the restrictions’ impact on CO2. One challenge is that CO2 remains in the atmosphere for hundreds of years, making it difficult to separate recent, local changes in emissions from remote signals. Climate variability also exerts a strong influence on the vegetation-atmosphere exchange of carbon, which complicates attribution of changes.
Capturing a 3D global picture of CO2 is impossible without satellite and models working together. OCO-2 observes CO2 in 10-kilometer-wide swaths worldwide with a 16-day repeat cycle. GMAO’s GEOS Constituent Data Assimilation System (CoDAS) ingests satellite data to fill gaps when and where observations are unavailable. Applied to OCO-2 data, it produces a high-resolution, complete picture of the CO2 in the atmosphere, including its vertical structure, every 6 hours.
For the COVID-19 impact study, “NCCS computing support was critical in helping us turn everything around so quickly,” said Lesley Ott, GMAO research meteorologist. “It was particularly tricky because we were working with a brand-new OCO-2 data version that was only released a few weeks prior and still had some gaps where data hadn't been processed.”
“That meant that we had to structure our runs differently,” Ott explained. “Instead of running a long, continuous period from 2014 to the present—which might take a few months—we did six parallel runs and used those to estimate the changes in 2020. It required a lot of work from NCCS to figure out how to structure and prioritize running all these jobs at once so that they could be completed in just a few weeks.”
Each of the six runs used 500 cores on the Discover supercomputer, with 1.5 terabytes of input data stored on Discover disk.
The results show noticeable CO2 decreases over Europe, North America, and Asia compared to earlier years. Attribution of these decreases remains uncertain because:
- their detection alone requires incredible accuracy and precision: decreases were less than 1 part per million (ppm) out of a total CO2 concentration of ~415 ppm, and
- variability in the Earth’s vegetation—notably over Australia, India, and Africa—produces a signal of similar magnitude.
NASA CO2 study data is publicly available on a new COVID-19 Earth Observing Dashboard built by NASA, ESA (European Space Agency), and JAXA (Japan Aerospace Exploration Agency), as well as the NASA Earthdata COVID-19 Dashboard.
- “NASA, Partner Space Agencies Amass Global View of COVID-19 Impacts,” NASA News Release 20-067, 6/24/20.
- “NASA, ESA, JAXA Release Global View of COVID-19 Impacts,” Goddard Media Studios, 6/25/20.
Jarrett Cohen, NASA Goddard Space Flight Center