Today, there is more carbon dioxide in the atmosphere than at any point in the past 3.6 million years. On April 5, atmospheric carbon dioxide exceeded 420 parts per million—marking nearly the halfway point toward doubling the carbon dioxide levels measured prior to the Industrial Revolution, a mere 171 years ago. Even amid a pandemic-induced economic shutdown—during which global annual emissions dropped 7 percent—carbon dioxide and methane levels set records in 2020. The last time Earth held this much carbon dioxide in its atmosphere, sea levels were nearly 80 feet higher and the planet was 7 degrees Fahrenheit warmer. The catch: Homo sapiens did not yet exist.
