Global carbon balance

Human emissions of $CO2$ now outpace natural sources by two orders of magnitude. The current concentration of $CO2$ has not been substantially exceeded in the past 30 million years. Multiple model exercises indicate that consuming all fossil fuels would result in concentrations more than double present levels, even after 10,000 years. The global warming effect of carbon emissions appears within 5–7 years. However, since the effect of present infrastructure over its expected life would only modestly increase $CO2$ concentrations and global temperature, human choices over its replacement will decisively influence ultimate carbon impacts, both short-term and long-term.