The influence of COVID-related emissions reductions on surface ocean pCO2 and pH

Abstract:

The stringent measures put in place by world governments to stop the spread of COVID-19 led to a global reduction in carbon dioxide (CO₂) emissions in the first half of 2020. Such a discrete reduction is comparable to annual emissions mitigation that may result from the Paris Agreement on Climate, although with different spatiotemporal patterns, and without the year on year cumulative reductions required to stabilize climate. Here, we utilize this natural experiment in the global carbon cycle to quantify the influence of the COVID-related CO₂ emissions reduction on two important quantities for ocean carbon: the surface ocean partial pressure of CO₂ (pCO₂) and the surface ocean pH, a measure of acidity. We analyze in situ measurements of these quantities across the global ocean and perform Earth system model experimentation to assess the likelihood of detecting meaningful change. Our findings from a suite of ensemble simulations conducted with the Canadian Earth System Model indicate that it may be possible to detect changes in surface ocean pCO₂ and surface ocean pH above the noise of internal variability across large regions of the tropics and subtropics with peak emission reductions of 25% in 2020. However, this detectability declines substantially for peak emission reductions of 10%. Even so, for the 25% reduction, the absolute magnitude of the anomalies are small (order -0.4 matm for pCO₂; order +0.002 for pH), and within the measurement uncertainty. Indeed, we do not find a measurable change in these quantities in the first half of 2020 from the in situ measurement record. Our results suggest that COVID-related emissions reductions will not have a measurable influence on ocean carbon unless they are large and sustained.