Wired – “Researchers have struggled to quantify in real time how much carbon dioxide humans spout. Lockdowns presented a unique opportunity to get a clearer picture…But now the Covid-19 pandemic has, oddly enough, helped give scientists a better top-down tool for estimating minute changes in fossil fuel emissions. A team of researchers used the UK’s coastal Weybourne Atmospheric Observatory to test air for carbon dioxide and oxygen separately, then summed the measurements together. Then they used a trick called atmospheric potential oxygen, or APO, which calculates the imbalance between oxygen and CO₂ from fossil fuel emissions. The key to separating natural and human-caused emissions is the ratio between CO₂ and oxygen. Plants process both in a one-to-one ratio: They absorb the same amount of carbon dioxide as the oxygen they expel, so the totals cancel each other out. Burning fossil fuels, on the other hand, consumes more oxygen than it produces CO₂…”

See also Ars Technica – “Elephant in the room”: Clean energy’s need for unsustainable minerals