Freshwater methane emissions offset the continental carbon sink. A study by David Bastviken, Lars J. Tranvik, John A. Downing, Patrick M. Crill, and Alex Enrich-Prast reveals that inland waters, such as lakes, reservoirs, streams, and rivers, emit significant amounts of methane (CH₄), which offsets a substantial portion of the estimated land carbon sink. The study found that freshwaters emit at least 103 Tg of CH₄ per year, equivalent to 0.65 Pg C as CO₂ equivalents per year, offsetting 25% of the estimated terrestrial greenhouse gas (GHG) sink. This suggests that the continental GHG sink may be overestimated, and freshwaters play a crucial role in the global carbon cycle. The terrestrial land surface is considered a significant GHG sink, with an estimated global land sink of 2.6 ± 1.7 Pg C yr⁻¹. However, lakes, impoundments, and rivers have not been fully included in the terrestrial GHG balance. Available data indicate that freshwaters can be substantial sources of both CO₂ and CH₄. Soil carbon reaches freshwaters through lateral hydrological transport, where it can be buried in sediments, transported to the sea, or released as CO₂ or CH₄ to the atmosphere. Although CH₄ emissions may be small in terms of carbon, they are more potent as a GHG than CO₂ over century timescales. The study compiled CH₄ emission estimates from 474 freshwater ecosystems with clearly defined emission pathways. Using recent data on the area and distribution of inland waters, the total CH₄ emission from freshwaters was estimated at 103 Tg CH₄ yr⁻¹. Expressed as CO₂ equivalents, this corresponds to 0.65 Pg C yr⁻¹, or 25% of the estimated terrestrial GHG sink. Ebullition and plant flux, which are poorly represented in the data set, dominate other flux pathways. Ebullition is likely underestimated due to its episodic nature and the limitations of short-term measurements. The study highlights that CH₄ emissions from freshwaters can significantly affect the global land GHG sink estimate. Proper consideration of ebullition and plant-mediated emissions may lead to increased future estimates of CH₄ emissions. Combining the current CH₄ emission estimate of 0.65 Pg C yr⁻¹ with the most recent estimate of freshwater CO₂ emissions (1.4 Pg C yr⁻¹) indicates that freshwaters are an important component of the continental GHG balance. Therefore, the terrestrial GHG sink may be smaller than currently believed, and data on GHG release from inland waters are needed for future revisions of net continental GHG fluxes.Freshwater methane emissions offset the continental carbon sink. A study by David Bastviken, Lars J. Tranvik, John A. Downing, Patrick M. Crill, and Alex Enrich-Prast reveals that inland waters, such as lakes, reservoirs, streams, and rivers, emit significant amounts of methane (CH₄), which offsets a substantial portion of the estimated land carbon sink. The study found that freshwaters emit at least 103 Tg of CH₄ per year, equivalent to 0.65 Pg C as CO₂ equivalents per year, offsetting 25% of the estimated terrestrial greenhouse gas (GHG) sink. This suggests that the continental GHG sink may be overestimated, and freshwaters play a crucial role in the global carbon cycle. The terrestrial land surface is considered a significant GHG sink, with an estimated global land sink of 2.6 ± 1.7 Pg C yr⁻¹. However, lakes, impoundments, and rivers have not been fully included in the terrestrial GHG balance. Available data indicate that freshwaters can be substantial sources of both CO₂ and CH₄. Soil carbon reaches freshwaters through lateral hydrological transport, where it can be buried in sediments, transported to the sea, or released as CO₂ or CH₄ to the atmosphere. Although CH₄ emissions may be small in terms of carbon, they are more potent as a GHG than CO₂ over century timescales. The study compiled CH₄ emission estimates from 474 freshwater ecosystems with clearly defined emission pathways. Using recent data on the area and distribution of inland waters, the total CH₄ emission from freshwaters was estimated at 103 Tg CH₄ yr⁻¹. Expressed as CO₂ equivalents, this corresponds to 0.65 Pg C yr⁻¹, or 25% of the estimated terrestrial GHG sink. Ebullition and plant flux, which are poorly represented in the data set, dominate other flux pathways. Ebullition is likely underestimated due to its episodic nature and the limitations of short-term measurements. The study highlights that CH₄ emissions from freshwaters can significantly affect the global land GHG sink estimate. Proper consideration of ebullition and plant-mediated emissions may lead to increased future estimates of CH₄ emissions. Combining the current CH₄ emission estimate of 0.65 Pg C yr⁻¹ with the most recent estimate of freshwater CO₂ emissions (1.4 Pg C yr⁻¹) indicates that freshwaters are an important component of the continental GHG balance. Therefore, the terrestrial GHG sink may be smaller than currently believed, and data on GHG release from inland waters are needed for future revisions of net continental GHG fluxes.