  Activity reductions in early 2020 due to the Coronavirus Disease 2019
pandemic led to unprecedented decreases in carbon dioxide (CO2) emissions.
Despite their record size, the resulting atmospheric signals are smaller than
and obscured by climate variability in atmospheric transport and biospheric
fluxes, notably that related to the 2019-2020 Indian Ocean Dipole. Monitoring
CO2 anomalies and distinguishing human and climatic causes thus remains a new
frontier in Earth system science. We show, for the first time, that the impact
of short-term, regional changes in fossil fuel emissions on CO2 concentrations
was observable from space. Starting in February and continuing through May,
column CO2 over many of the World's largest emitting regions was 0.14 to 0.62
parts per million less than expected in a pandemic-free scenario, consistent
with reductions of 3 to 13 percent in annual, global emissions. Current
spaceborne technologies are therefore approaching levels of accuracy and
precision needed to support climate mitigation strategies with future missions
expected to meet those needs.
