evidence: Carbon dioxide (CO2) is an important heat-trapping gas, also known as a greenhouse gas, that comes from the extraction and burning of fossil fuels (such as coal, oil, and natural gas), from wildfires, and natural processes like volcanic eruptions. The first graph shows atmospheric CO2 levels measured by NOAA at Mauna Loa Observatory, Hawaii, since 1958. The second graph shows CO2 levels during Earth’s last three glacial cycles, as captured by air bubbles trapped in ice sheets and glaciers. Since the onset of industrial times in the 18th century, human activities have raised atmospheric CO2 by 50% – meaning the amount of CO2 is now 150% of its value in 1750. This human-induced rise is greater than the natural increase observed at the end of the last ice age 20,000 years ago. [...] This boom-and-bust cycle of plant growth gives the graph of CO2 a sawtooth pattern of ups and downs from year to year. At a larger scale, the upward climb of the trend line over the decades is caused by CO2 emissions, primarily from burning fossil fuels. Thus, the data illustrate both natural factors and human additions of CO2.