"For centuries **before 1800, CO2 levels fluctuated narrowly at close to 270 parts per million** (ppm)—that is, 0.027 percent by volume. **By 1900 they rose slightly to 290 ppm, a century later they were nearly 375 ppm, and in the summer of 2020 they rose above 420 ppm**, more than a 50 percent increase above the late 18th-century level. "**Preindustrial methane levels were three orders of magnitude lower—less than 800 parts per billion** (ppb)—**but they have more than doubled, to nearly 1,900 ppb by 2020**, while nitrous oxide concentrations rose from about 270 ppb to more than 300 ppb." ([Location 3485](https://readwise.io/to_kindle?action=open&asin=B08SGC3TD3&location=3485)) --- **Tags** -- [[quotes]], [[decarbonisation]], [[carbon-dioxide]], [[climate-change]], [[methane]], [[nitrous-oxide]], [[nitrogen]] **Source** -- [[202412030828 - B - How the World Really Works]]