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    caption: 'Present-day atmospheric levels of carbon dioxide, methane, and nitrous oxide are notably higher than their pre-industrial averages of 280, 0.7, and 0.27 parts per million (ppm) by volume, respectively (left). Air sampling data from 1958 to 2013 show long-term increases due to human activities as well as short-term variations due to natural biogeochemical processes and seasonal vegetation growth (right). (Figure sources: (left) Forster et al. 2007<tbib>f2b357c2-f4ae-4868-a058-e48fbdbb1303</tbib>; (right) Scripps Institution of Oceanography and NOAA Earth Systems Research Laboratory).'
    chapter_identifier: appendix-climate-science-supplement
    create_dt: 2013-11-19T17:32:00
    identifier: heattrapping-gas-levels
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    title: Heat-Trapping Gas Levels
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title: 'Heat-Trapping Gas Levels - Left'
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