ABSTRACT
Atmospheric methane growth reached an exceptionally high rate of 15.1 ± 0.4 parts per billion per year in 2020 despite a probable decrease in anthropogenic methane emissions during COVID-19 lockdowns1. Here we quantify changes in methane sources and in its atmospheric sink in 2020 compared with 2019. We find that, globally, total anthropogenic emissions decreased by 1.2 ± 0.1 teragrams of methane per year (Tg CH4 yr-1), fire emissions decreased by 6.5 ± 0.1 Tg CH4 yr-1 and wetland emissions increased by 6.0 ± 2.3 Tg CH4 yr-1. Tropospheric OH concentration decreased by 1.6 ± 0.2 per cent relative to 2019, mainly as a result of lower anthropogenic nitrogen oxide (NOx) emissions and associated lower free tropospheric ozone during pandemic lockdowns2. From atmospheric inversions, we also infer that global net emissions increased by 6.9 ± 2.1 Tg CH4 yr-1 in 2020 relative to 2019, and global methane removal from reaction with OH decreased by 7.5 ± 0.8 Tg CH4 yr-1. Therefore, we attribute the methane growth rate anomaly in 2020 relative to 2019 to lower OH sink (53 ± 10 per cent) and higher natural emissions (47 ± 16 per cent), mostly from wetlands. In line with previous findings3,4, our results imply that wetland methane emissions are sensitive to a warmer and wetter climate and could act as a positive feedback mechanism in the future. Our study also suggests that nitrogen oxide emission trends need to be taken into account when implementing the global anthropogenic methane emissions reduction pledge5.
Subject(s)
Atmosphere , Methane , Wetlands , Humans , Communicable Disease Control/statistics & numerical data , COVID-19/epidemiology , Methane/analysis , Ozone/analysis , Atmosphere/chemistry , Human Activities/statistics & numerical data , Time Factors , History, 21st Century , Temperature , Humidity , Nitrogen Oxides/analysisABSTRACT
The outbreak of coronavirus disease 2019 (COVID-19) showed various transmission rate (R t ) across different regions. The determination of the factors affecting transmission rate is urgent and crucial to combat COVID-19. Here we explored variation of R t between 277 regions across the globe and the associated potential socioeconomic, demographic, and environmental factors. At global scale, the R t started to decrease approximately 2 weeks after policy interventions initiated. This lag from the date of policy interventions initiation to the date when R t started to decrease ranges from 9 to 19 days, largest in Europe and North America. We find that proportion of elderly people or life expectancy can explain ~50% of variation in transmission rate across the 277 regions. The transmission rate at the point of inflection (R I ) increases by 29.4% (25.2-34.0%) for 1% uptick in the proportion of people aged above 65, indicating that elderly people face ~2.5 times higher infection risk than younger people. Air temperature is negatively correlated with transmission rate, which is mainly attributed to collinearities between air temperature and demographic factors. Our model predicted that temperature sensitivity of R I is only -2.7% (-5.2-0%) per degree Celsius after excluding collinearities between air temperature and demographic factors. This low temperature sensitivity of R I suggests that a warm summer is unlikely to impede the spread of COVID-19 naturally.