evidence: Carbon dioxide measured at NOAA’s Mauna Loa Atmospheric Baseline Observatory peaked for 2022 at 421 parts per million in May, pushing the atmosphere further into territory not seen for millions of years, scientists from NOAA and Scripps Institution of Oceanography offsite link at the University of California San Diego announced today. [...] Prior to the Industrial Revolution, CO2 levels were consistently around 280 ppm for almost 6,000 years of human civilization. Since then, humans have generated an estimated 1.5 trillion tons of CO2 pollution offsite link, much of which will continue to warm the atmosphere for thousands of years. CO2 levels are now comparable to the Pliocene Climatic Optimum, between 4.1 and 4.5 million years ago, when they were close to, or above 400 ppm. During that time, sea levels were between 5 and 25 meters higher than today offsite link, high enough to drown many of the world’s largest modern cities. Temperatures then averaged 7 degrees Fahrenheit higher than in pre-industrial times, and studies indicate offsite link that large forests occupied today’s Arctic tundra.