Emission reductions during COVID-19 enhance marine heatwave over the North Pacific in spring 2020

Severe marine heatwave over the North Pacific was observed in spring 2020, which likely caused the record Arctic ozone loss. Here we show that this anomalous North Pacific warming is related to the emission reductions during COVID-19 which emerged in China in early 2020 and spread rapidly. We show simulated evidence that the emission reductions during COVID-19 likely contribute to about 28.5% of the northeastern Pacific heatwave in spring 2020. On the one hand, the emission reductions excited a wave train from East Asia to the northeastern Pacific, which results in weakening of mid-latitude westerlies and a reduction in evaporation over the North Pacific. This tends to warm the ocean surface and enhances the northeastern Pacific heatwave. On the other hand, changes in aerosols by the downwind transport modify the clouds over the North Pacific. This indirect aerosol effect plays a minor role in the heatwave. These results suggest that the abrupt reductions in aerosol emissions may enhance the probability of the occurrence of North Pacific heatwave.