Urbanization can accelerate climate change by increasing soil N2O emission while reducing CH4 uptake

Abstract Urban land‐use change has the potential to affect local to global biogeochemical carbon (C) and nitrogen (N) cycles and associated greenhouse gas (GHG) fluxes. We conducted a meta‐analysis to (1) assess the effects of urbanization‐induced land‐use conversion on soil nitrous oxide (N 2 O) and methane (CH 4 ) fluxes, (2) quantify direct N 2 O emission factors (EF d ) of fertilized urban soils used, for example, as lawns or forests, and (3) identify the key drivers leading to flux changes associated with urbanization. On average, urbanization increases soil N 2 O emissions by 153%, to 3.0 kg N ha −1 year −1 , while rates of soil CH 4 uptake are reduced by 50%, to 2.0 kg C ha −1 year −1 . The global mean annual N 2 O EF d of fertilized lawns and urban forests is 1.4%, suggesting that urban soils can be regional hotspots of N 2 O emissions. On a global basis, conversion of land to urban greenspaces has increased soil N 2 O emission by 0.46 Tg N 2 O‐N year −1 and decreased soil CH 4 uptake by 0.58 Tg CH 4 ‐C year −1 . Urbanization driven changes in soil N 2 O emission and CH 4 uptake are associated with changes in soil properties (bulk density, pH, total N content, and C/N ratio), increased temperature, and management practices, especially fertilizer use. Overall, our meta‐analysis shows that urbanization increases soil N 2 O emissions and reduces the role of soils as a sink for atmospheric CH 4 . These effects can be mitigated by avoiding soil compaction, reducing fertilization of lawns, and by restoring native ecosystems in urban landscapes.