Live Science reports:

Within a human lifetime, concentrations of CO₂ in Earth’s atmosphere could reach levels associated with 19 “mass extinctions” that have taken place in the last 534 million years, new research suggests.

By 2100, atmospheric carbon dioxide levels could rise to 800 parts per million by volume (ppmv) — almost double the concentration of roughly 421 ppmv recorded this year — if we fail to curb emissions from burning fossil fuels and converting land for agriculture.

That would be edging close to the average CO₂ concentrations (870 ppmv) associated with huge crashes in marine biodiversity over the last 534 million years, according to a study published June 22 in the journal Earth’s Future. These extinction events are preserved in the fossil record, allowing scientists to plot how biodiversity and atmospheric CO₂ evolved throughout Earth’s history.

“The relationship between carbon dioxide in the past and extinction in the past gives us a kind of yardstick that we can apply to the present,” study author William Jackson Davis, a biologist and president of the non-profit Environmental Studies Institute in Santa Cruz, California, told Live Science.

Atmospheric CO₂ contributes to biodiversity loss via ocean acidification, Davis said. The oceans soak up atmospheric carbon dioxide, which turns the water more acidic, reducing the availability of calcium carbonate ions needed for organisms to build their skeletons and shells. When these effects are strong enough to affect the entire food chain, they can lead to mass extinctions. [Continue reading…]