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<blockquote data-quote="Jones" data-source="post: 3284235" data-attributes="member: 4805">We know human activities are driving the increase in CO2 concentrations because atmospheric CO2 contains information about its source. Scientists can tease apart how much CO2 comes from natural sources, and how much comes from combusted fossil fuel sources.&nbsp;Compared to other carbon sources, carbon from fossil fuels has a distinctly different “signature,” essentially the relative amount of heavier or lighter atoms of carbon (technically δ13C). The more negative the δ13C, the higher the proportion of carbon from fossil fuels.&nbsp;Over the years, δ13C has decreased while the overall amount of CO2 has increased. This information tells scientists that fossil fuel emissions are the largest contributor of CO2 concentrations since the pre-industrial era.<img src="https://www.ucsusa.org/sites/default/files/images/2017/07/CO2_signature%20.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />Direct Evidence of Fossil Fuel Derived CO2 in the Atmosphere. While the concentration of carbon has increased, the carbon originating from natural sources has decreased. </blockquote>

[QUOTE="Jones, post: 3284235, member: 4805"] [I]We know human activities are driving the increase in CO2 concentrations because atmospheric CO2 contains information about its source. Scientists can tease apart how much CO2 comes from natural sources, and how much comes from combusted fossil fuel sources. Compared to other carbon sources, carbon from fossil fuels has a distinctly different “signature,” essentially the relative amount of heavier or lighter atoms of carbon (technically δ13C). The more negative the δ13C, the higher the proportion of carbon from fossil fuels. Over the years, δ13C has decreased while the overall amount of CO2 has increased. This information tells scientists that fossil fuel emissions are the largest contributor of CO2 concentrations since the pre-industrial era. [IMG]https://www.ucsusa.org/sites/default/files/images/2017/07/CO2_signature%20.jpg[/IMG] Direct Evidence of Fossil Fuel Derived CO2 in the Atmosphere. While the concentration of carbon has increased, the carbon originating from natural sources has decreased. [/I] [/QUOTE]

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