For 800,000 years before the twentieth century, carbon dioxide levels in Earth’s atmosphere never exceeded 300 parts per million. In March 2015, the monthly average went above 400 ppm for the first time.
For 800,000 years before the twentieth century, carbon dioxide levels in Earth’s atmosphere never exceeded 300 parts per million. In March 2015, the monthly average went above 400 ppm for the first time.