Separation of biospheric and fossil fuel fluxes of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; by atmospheric inversion of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and &amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; measurements: Observation System Simulations