Since 2011 (measurements reported in AR5), concentrations have continued to increase in the atmosphere, reaching annual averages of 410 parts per million (ppm) for carbon dioxide (CO 2), 1866 parts per billion (ppb) for methane (CH 4), and 332 ppb for nitrous oxide (N 2O) in 2019.6 Land and ocean have taken up a near-constant proportion (globally about 56% per year) of CO 2 emissions from human activities over the past six decades, with regional differences