A graph depicting CO<sub>2</sub> levels from 1958 to 2009 as measured at Mauna Loa, Hawaii. Year is on the <i>x</i>-axis, atmospheric carbon dioxide concentration (in parts per million) is on the <i>y</i>-axis. The cause for the yearly rise and fall is the annual cycle of plant respiration. The cause of the increasing trend is the anthropogenic release of CO<sub>2</sub>, mainly due to the use of fossil energy sources.
<a href="//commons.wikimedia.org/wiki/User:Hanno" title="User:Hanno">Hanno</a>
Graph drawn by <a href="//commons.wikimedia.org/wiki/User:Hanno" title="User:Hanno">Hanno</a> using data published on the web by P. Tans (2007) as "Monthly mean atmospheric carbon dioxide at Mauna Loa Observatory, Hawaii ". Global Monitoring Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, U.S.A. <a rel="nofollow" class="external autonumber" href="http://www.cmdl.noaa.gov/ccgg/trends/co2_data_mlo.php">[1]</a>