Latest published assessments of anthropogenic carbon dioxide (CO2) emissions, collated by the Global Carbon Project, suggest that anthropogenic sources represent about 6% of total CO2 emissions into the atmosphere. However, although natural CO2 emissions are much larger than those from anthropogenic sources, the fluxes between natural CO2 sources and sinks are essentially in balance within the carbon cycle and the impact of anthropogenic emissions is such that they have been responsible for the increase in atmospheric CO2 concentration since pre-industrial times. This is the main driver of long-term global temperature rise.
Le Quéré et al, 2013. The global carbon budget 1959-2011. Earth Syst. Sci. Data, 5, 165-185. doi: 10.5194/essd-5-165-2013.