Life cycle assessment integration into energy system models: An application for Power-to-Methane in the EU

•Study covers five energy sectors, 18 impact categories and 31 countries in Europe.•Indirect CO2 emissions can be one to three times higher than direct emissions.•Electricity for PtM has to be below 123–181 gCO2eq/kWh to achieve climate benefits.•PtM has similar or lower impact than natural gas for 10 out of 18 categories.