This figure shows the history of <a href="https://en.wikipedia.org/wiki/Earth%27s_atmosphere" class="extiw" title="w:Earth's atmosphere">atmospheric</a> <a href="https://en.wikipedia.org/wiki/carbon_dioxide" class="extiw" title="w:carbon dioxide">carbon dioxide</a> concentrations as directly measured at <a href="https://en.wikipedia.org/wiki/Mauna_Loa" class="extiw" title="w:Mauna Loa">Mauna Loa</a>, <a href="https://en.wikipedia.org/wiki/Hawaii" class="extiw" title="w:Hawaii">Hawaii</a>.  This curve is known as the <a href="https://en.wikipedia.org/wiki/Keeling_curve" class="extiw" title="w:Keeling curve">Keeling curve</a>, and is an essential piece of evidence of the man-made increases in <a href="https://en.wikipedia.org/wiki/greenhouse_gas" class="extiw" title="w:greenhouse gas">greenhouse gases</a> that are believed to be the cause of <a href="https://en.wikipedia.org/wiki/global_warming" class="extiw" title="w:global warming">global warming</a>.  The longest such record exists at Mauna Loa, but these measurements have been independently confirmed at many other sites around the world <a rel="nofollow" class="external autonumber" href="http://cdiac.ornl.gov/trends/co2/contents.htm">[2]</a>.  The annual fluctuation in carbon dioxide is caused by seasonal variations in carbon dioxide uptake by land <a href="https://en.wikipedia.org/wiki/plant" class="extiw" title="w:plant">plants</a>.  Since many more forests are concentrated in the <a href="https://en.wikipedia.org/wiki/Northern_Hemisphere" class="extiw" title="w:Northern Hemisphere">Northern Hemisphere</a>, more carbon dioxide is removed from the atmosphere during Northern Hemisphere <a href="https://en.wikipedia.org/wiki/summer" class="extiw" title="w:summer">summer</a> than <a href="https://en.wikipedia.org/wiki/Southern_Hemisphere" class="extiw" title="w:Southern Hemisphere">Southern Hemisphere</a> summer.  This annual cycle is shown in the inset figure by taking the average concentration for each month across all measured years.  The grey curve shows the average monthly concentrations, and red curve is a moving 12 month average.
<ul><li><a href="//commons.wikimedia.org/wiki/File:Mauna_Loa_Carbon_Dioxide-nl.svg" title="File:Mauna Loa Carbon Dioxide-nl.svg">File:Mauna Loa Carbon Dioxide-nl.svg</a>: *<a href="//commons.wikimedia.org/wiki/File:Mauna_Loa_Carbon_Dioxide-en.svg" title="File:Mauna Loa Carbon Dioxide-en.svg">_Mauna_Loa_Carbon_Dioxide-en.svg</a>: <a href="//commons.wikimedia.org/wiki/User:S%C3%A9mhur" title="User:Sémhur">Sémhur</a></li>
<li>derivative work: <a href="//commons.wikimedia.org/w/index.php?title=User:Pirumbaut&amp;action=edit&amp;redlink=1" class="new" title="User:Pirumbaut (page does not exist)">Pirumbaut</a> (<a href="//commons.wikimedia.org/wiki/User_talk:Pirumbaut" title="User talk:Pirumbaut"><span class="signature-talk">talk</span></a>)</li>
<li>derivative work: [[User:{{subst:Sémhur}}|{{subst:Sémhur}}]]</li></ul>
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