The worldwide lockdown in response to the COVID-19 pandemic in the year 2020 led to an economic slowdown and dramatically changed peoples' lives around the world. On the bright side, fossil fuel CO2 emissions were reduced by 8% in the first 4 months of 2020 due to reduced transportation, industrial and power generation, and an anticipated annual reduction of 4%-7%. Although this reduction was short-lived since the economic activities rebounded subsequently and did not occur synchronously in different regions, the COVID-19 pandemic provides an unintended experiment opportunity for the scientific community to monitor and understand the atmosphere response to the emission reduction.
To answer the question of how big is the impact of this emission reduction on the increasing trend of atmospheric CO2 concentration, there are two major challenges. The magnitude of change is within the capability of high-accuracy CO2 analyzers, but relatively small for carbon-detecting satellites. In addition, atmospheric CO2 is strongly affected by the changes in vegetation and atmospheric transport shortly after the change of fossil fuel emission. Over a long enough period of time, a new balance of CO2 will be established between the atmosphere, the land biosphere, and the ocean.
In a recently published Environmental Research Letter article, Ning Zeng from the University of Maryland and twelve collaborators from multiple international research institutes explored these questions by combining carbon cycle models and space-borne and grounded-based observations. The model and GOSAT carbon satellite results revealed an average of 0.14 ppm decrease in the atmospheric column CO2 anomaly in the Northern Hemisphere for the latitude band between 0 to 45ºN for February-April 2020. This is the largest decrease in the last 10 years and is mainly due to COVID and weather variability based on model sensitivity experiments. However, the anomalies at the Hawaii station showed a sub-annual signal of 1-2 ppm in the atmospheric background CO2 concentration. Although the short-duration of the 2020 COVID-19 lockdown only has left a small signature in the atmospheric CO2, this study suggested that current modeling capabilities can sufficiently capture the observed sub-annual variabilities. Continued efforts to improve and expand model and observation (e.g. ground, aircraft and satellite platforms) capabilities will be critical for monitoring and verification of fossil fuel emissions reduction targets to achieve our climate goals.
Funding for this project was provided by the NOAA Climate Program Office, MAPP program.
Read the full study here.