One-third of global lake nitrous oxide emissions are concentrated in the northern temperate zone (40°N–50°N)

Lacustrine nitrous oxide (N 2 O) emissions remain highly uncertain in the global greenhouse gas budget largely because of sparse observations and the omission of small lakes. Here we compile the Global Lake N 2 O database (GLON 2 O), integrating 6550 in situ measurements from 3829 lakes worldwide, and develop a machine learning framework to estimate emissions from lakes ≥0.1 square kilometers. To quantify previously overlooked systems, we construct the Global Small Lakes database (GSLAKES). We estimate that global lakes emit 0.208 teragrams of nitrogen per year of N 2 O, with approximately one-third originating from the northern temperate zone (40° to 50°N). Despite accounting for only 9.6% of total lake area, small lakes (<0.1 square kilometers) contribute 34.6% of global emissions, revealing a pronounced U-shaped relationship between emission intensity and lake size. We further identify hierarchical predictors of lake N 2 O emissions: Natural constraints determine biogeochemical potential, anthropogenic nitrogen inputs amplify emissions, and lake morphometry regulates spatial expression. These findings refine global lake N 2 O inventories and provide an empirical basis for scale-aware mitigation.