On May 9, 2013, the daily average carbon dioxide measured at Mauna Loa surpassed 400 ppm for the first time on record.
Greenhouse Gas Emissions and Sinks: 1990—2018 yields a result of 200 metric tons of carbon per hectare or 81 metric tons of carbon per acre for the carbon stock density of U.
The average carbon coefficient of natural gas burned in 2018 is 14.