Groundwater depletion contributes to an increase in global carbon emissions

Carbon emissions from groundwater depletion (GWD) can be involved in the global carbon cycle; however, it is poorly understood that how much contribution they have. We here generate two maps on global GWD using measurements from >171,000 monitoring wells and on global groundwater bicarbonate (HCO₃⁻) concentrations using the meta data from 28,902 measurements. We then evaluate the global GWD-induced carbon emissions and show that 1) the total emissions from GWD can be a type of significant source (52 ± 18 MMT CO₂ yr⁻¹) within the global carbon cycle, which have exceeded the net emissions of grasslands (~35 MMT CO₂ yr⁻¹), one of the world's main carbon sources; 2) the total GWD is approximately 550 ± 73 km³/year in recent 20 years, which is generally consistent with previous studies; 3) China (6.7 ± 1.6 MMT CO₂ yr⁻¹), Brazil (6.6 ± 2.5MMT CO₂ yr⁻¹), and India (5.8 ± 1.5 MMT CO₂ yr⁻¹) are the top three contributors of GWD-induced carbon emissions.