This briefing paper explains how policymakers can account for well-to-wake (WTW) carbon dioxide equivalent (CO2e) emissions in strategies that aim to monitor or regulate climate-warming pollutants from ships. Well-to-wake emissions, or life-cycle emissions, are the sum of upstream (well-to-tank) and downstream (tank-to-wake) emissions. In addition to carbon dioxide (CO2), carbon dioxide equivalents include greenhouse gases (GHGs) such as methane (CH4) and nitrous oxide (N2O), as well as particles like black carbon (BC). By focusing solely on CO2 and ignoring other pollutants, regulators would significantly underestimate climate pollution from maritime transport which would work against achieving the Paris Agreement goal to limit global warming to 1.5°C compared to pre-industrial levels.