Between 400k years ago until 1950, the levels of carbon dioxide in the atmosphere never exceeded [100 / 200 / 300 / 400] parts per million (ppm). Today, carbon dioxide levels have exceeded [300 / 410 / 500 / 550] parts per million (ppm).
Between 400k years ago until 1950, the levels of carbon dioxide in the atmosphere never exceeded 300 parts per million (ppm). Today, carbon dioxide levels have exceeded 410 parts per million (ppm).
