In the spring of 2020, as the COVID-19 pandemic brought global industry and travel nearly to a halt, satellite sensors recorded a dramatic plunge in nitrogen dioxide, a byproduct of internal combustion engines and heavy industry. For a moment, the world’s air was cleaner than it had been in decades.
But then something strange started happening: methane, the second most important anthropogenic greenhouse gas after carbon dioxide, was surging. Its growth rate hit 16.2 parts per billion that…