In the past 60 million years, there have been periods in Earth’s history when CO 2 concentrations were significantly higher than at present, but multiple lines of evidence show that the rate at which CO 2 has increased in the atmosphere during 1900–2019 is at least 10 times faster than at any other time during the last 800,000 years (high confidence), and 4–5 times faster than during the last 56 million years