Methane Emission From Global Lakes: New Spatiotemporal Data and Observation-Driven Modeling of Methane Dynamics Indicates Lower Emissions

Lakes have been highlighted as one of the largest natural sources of the greenhouse gas methane (CH4) to the atmosphere. However, global estimates of lake CH4 fluxes over the last 20 years exhibit widely different results ranging from 6 to 185 Tg CH4 yr −1, which is to a large extent driven by differences in lake areas and thaw season lengths used. This has generated uncertainty regarding both lake fluxes and the global CH4 budget. This study constrains global lake water CH4 emissions by using new information on lake area and distribution and CH4 fluxes distinguished by major emission pathways; ecoclimatic lake type; satellite-derived ice-free emission period length; and diel- and temperature-related seasonal flux corrections. We produced gridded data sets at 0.25° latitude × 0.25° longitude spatial resolution, representing daily emission estimates over a full annual climatological cycle, appropriate for use in global CH4 budget estimates, climate and Earth System Models, bottom-up biogeochemical models, and top-down inverse model simulations. Global lake CH4 fluxes are 41.6 ± 18.3 Tg CH4 yr −1 with approximately 50% of the flux contributed by tropical/subtropical lakes. Strong temperature-dependent flux seasonality and satellite-derived freeze/thaw dynamics limit emissions at high latitudes. The primary emission pathway for global annual lake fluxes is ebullition (23.4 Tg) followed by diffusion (14.1 Tg), ice-out and spring water-column turnover (3.1 Tg), and fall water-column turnover (1.0 Tg). These results represent a major contribution to reconciling differences between bottom-up and top-town estimates of inland aquatic system emissions in the global CH4 budget. Plain Language Summary A greenhouse gas which contributes significantly to global warming is methane (CH4). Atmospheric concentrations of CH4 have more than doubled since the pre-industrial era primarily due to emissions from human activities. Inland waters (i.e., wetlands, lakes, rivers, and reservoirs) are significant CH4 emitters yet still represent a major challenge in quantifying the global CH4 budget. This investigation presents an observation-based analysis of global lake area and CH4 emissions and addresses multiple uncertainties and gaps in recent global estimates of CH4 emission from lakes. We show that lakes occupy a global area of around 2,800,000 km 2 (comparable to the size of Argentina) and release ∼42 million tons of CH4 per year to the atmosphere. This study identifies both methods and data sources from other recent studies that contribute to overestimating lake emissions. We produce a suite of global gridded data sets representing lake area and distribution, lake type, observed freeze-thaw periods, and daily CH4 emissions for a full annual cycle.