China's strict covid-19 lockdowns in China last year reduced air pollution in many cities. This was a temporary clean-up that saved thousands of lives. It appears that China's spring bloom was brought forward by the clearer skies last year, which led to so much vegetation growth that it was nearly a fifth greener than previous years.
Fenzhen Su, from the Chinese Academy of Sciences, and his colleagues used mobile location data from technology company Baidu to determine how many people moved around large cities between January 2020 and April 2020. Pre-pandemic movement saw movement drop by more than half between 23 February and 9 February. Movement only started to return to pre-pandemic levels around mid-March.
The team combined the mobility index with data about nitrogen dioxide, an air pollutant most commonly produced by cars, and satellite data to determine the haziness of air, how much sunlight is reaching vegetation for photosynthesis.
The spring months 2020 had more sunshine than the previous years. The greatest relative change occurred between January and February, at the same time that the peak of covid-19 restriction.
China's overall greenness was 17% higher than in the previous five years. This is measured using an index of leaf coverage per unit of land. This index shows that the spring bloom arrived 8.4 weeks earlier than the average date for 2015-2019, which was 6 April.
According to the authors, the lockdowns and the timing of the changes suggest that photosynthesis was boosted by the reductions in pollution. Their findings show that nature can rebound quickly across large areas when pressures from humans are reduced, even if this was temporary.
Journal reference: Science Advances, DOI: 10.1126/sciadv.abe8044