Abstract This study discusses the potential of H2 production by proton exchange membrane water electrolysis as an effective option to reduce greenhouse gas emissions in the hydrogen sector. To address this topic, a life cycle assessment is conducted to compare proton exchange membrane water electrolysis versus the reference process - steam methane reforming. As a relevant result we show that hydrogen production via proton exchange membrane water electrolysis is a promising technology to reduce CO2 emissions of the hydrogen sector by up to 75%, if the electrolysis system runs exclusively on electricity generated from renewable energy sources. In a future (2050) base-load operation mode emissions are comparable to the reference system. The results for the global warming potential show a strong reduction of greenhouse gas emissions by 2050. The thoroughly and in-depth modeled components of the electrolyser have negligible influence on impact categories; thus, emissions are mainly determined by the electricity mix. With 2017 electricity mix of Germany, the global warming potential corresponds to 29.5 kg CO2 eq. for each kg of produced hydrogen. Referring to the electricity mix we received from an energy model emissions can be reduced to 11.5 kg CO2 eq. in base-load operation by the year 2050. Using only the 3000 h of excess power from renewables in a year will allow for the reduction of the global warming potential to 3.3 kg CO2 eq. From this result we see that an environmentally friendly electricity mix is crucial for reducing the global warming impact of electrolytic hydrogen.