Greenhouse gas emissions from lakes and impoundments: Upscaling in the face of global change

Lakes and impoundments are important sources of greenhouse gases (GHG: i.e., CO₂, CH₄, N₂O), yet global emission estimates are based on regionally-biased averages and elementary upscaling. We assembled the largest global dataset to date on emission rates of all three GHGs and found they covary with lake size and trophic state. Fitted models were upscaled to estimate global emission using global lake size inventories and a remotely-sensed global lake productivity distribution. Traditional upscaling approaches overestimated CO₂ and N₂O emission but underestimated CH₄ by half. Our upscaled size-productivity weighted estimates (1.25-2.30 Pg of CO₂-equivalents annually) are nearly 20% of global CO₂ fossil fuel emission with ~75% of the climate impact due to CH₄. Moderate global increases in eutrophication could translate to 5-40% increases in the GHG effects in the atmosphere, adding the equivalent effect of another 13% of fossil fuel combustion or an effect equal to GHG emissions from current land use change.