Reductions in California's Urban Fossil Fuel CO₂ Emissions During the COVID‐19 Pandemic

Abstract

Fossil fuel carbon dioxide (CO₂) emissions (ffCO₂) constitute the majority of greenhouse gas emissions and are the main determinant of global climate change. The COVID-19 pandemic caused wide-scale disruption to human activity and provided an opportunity to evaluate our capability to detect ffCO₂ emission reductions. Quantifying changes in ffCO₂ levels is especially challenging in cities, where climate mitigation policies are being implemented but local emissions lead to spatially and temporally complex atmospheric mixing ratios. Here, we assess ffCO₂ emission patterns associated with pandemic-induced changes to human activity using direct observations of on-road CO₂ mole fractions in the Los Angeles (LA) urban area and analyses of the radiocarbon (¹⁴C) content of annual grasses collected by community scientists throughout California, USA. With COVID-19 mobility restrictions in place in 2020, we observed a significant reduction in ffCO₂ levels across California, especially in urban centers. In LA, on-road CO₂ enhancements were 60 ± 16% lower than the corresponding period of 2019 and rebounded to pre-pandemic levels by 2021. Plant ¹⁴C analysis indicated ffCO₂ reductions of 5 ± 10 ppm in 2020 relative to pre-pandemic observations in LA. However, ffCO₂ emission trajectories varied substantially by region and sector as COVID-related restrictions were relaxed. Further development of these techniques could aid efforts to monitor decarbonization in cities, especially in developing countries without established CO₂ monitoring infrastructure.