Emissions of CO2 due to volcanic activity, though sometimes large on a local scale, are relatively minor on a global scale, accounting for 0.02-0.05 Pg C/year. Of more importance, climate-wise, is the release of aerosols from volcanic eruptions, as these can cause a net cooling of the planet's climate.
Although fires caused by lightning strikes have accounted, and still do account, for some large biomass burning events - and thus emissions of CO2 - the impact of this source on atmospheric CO2 concentrations is relatively short term due to rapid uptake of CO2 during regrowth of vegetation. Globally, direct and indirect biomass burning activities of humans in the past few centuries have dwarfed emissions from such natural biomass burning. Let us now consider this and the numerous other anthropogenic sources of CO2.
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