The release of CO2 from belowground autotrophic and heterotrophic respiration to the atmosphere, soil CO2 efflux, is the largest component of ecosystem respiration and perhaps the largest individual component flux of the terrestrial carbon cycle. Direct measurements of gas exchange between the soil surface and the atmosphere are used to estimate soil CO2 efflux and average values that integrate its variation among measured locations are directly scaled to land areas (stand to region). Errors associated with measurements of soil CO2 efflux are further compounded when scaling to larger areas because these larger spatial areas are fundamentally different than the area where the flux was measured. In fact, this particular scaling issue results in a systematic overestimation of the measured flux. However, it remains unclear how this systematic error propagates to influence our understanding of the global carbon budget.
Here we show that a systematic error associated with scaling soil CO2 efflux from measurements to forest ecosystems overestimates the global flux attributed to this process by a magnitude comparable to other major global CO2 fluxes. We expect that establishing the magnitude and global significance of this systematic error in scaling soil CO2 efflux will provide a path forward for more accurate reporting of this flux and ultimately aid in constraining the global carbon budget. For example, future reports of soil CO2 efflux can be scaled appropriately with little additional effort and their results can be synthesized to provide more accurate estimates of this flux at a global scale. Finally, the current overestimation of the contribution of soil CO2 efflux to the global carbon budget suggests that the capacity for terrestrial or oceanic ecosystems to act as carbon sinks has been underestimated.