Abstract In an effort to combat climate change, the International Maritime Organization (IMO) has set ambitious goals for the reduction of greenhouse gas emissions from ships, with a target of at least a 50% reduction of total annual greenhouse gas (GHG) emissions, including carbon, from 2008 levels by 2050, with a further goal of zero GHG emissions within this century. Numerous technologies are under development to address these new goals, but the implementation of these new technologies is quite uncertain. Cargo ship owners face the challenge of determining how to best employ and possibly upgrade the current fleet to meet interim goals while awaiting the maturation of future technologies. This article describes a methodology and computer code that provide a rapid assessment of the impact of various fuel-saving technologies on an existing cargo ship’s fuel consumption, thus providing the ship owner fundamental data indicating which upgrades and practices warrant further, more detailed investigation.</jats:p> </jats:sec> <jats:sec> <jats:title>Background</jats:title> <jats:p>According to the National Oceanic and Atmospheric Administration, the amount of carbon dioxide in the atmosphere has increased by 1.78 ppm per year on average since 1980, and the increase is accelerating. Through the 1980s and 1990s, the increase was around 1.5–1.6 ppm per year, but the growth rate has averaged 2.4 ppm per year since 2010 (Tans et al. 2020).</jats:p> <jats:p>Rising levels of carbon dioxide in the atmosphere adversely impact the environment in many ways. For example, increased levels of carbon dioxide dissolving in sea water increase the acidity of the oceans; as pH levels drop, organisms like oysters and corals have trouble maintaining their hard shells and skeletons made from calcium carbonate. If pH levels get too low, the calcium carbonate structures begin dissolving (NOAA 2020). Another example can be found in the NOAA Arctic Report Card in which each year shows an Arctic that is becoming warmer, less frozen, and more fragile; the 2020 report includes data on high land-surface air temperatures, low snow extent, low minimum sea-ice extent, and extreme wildfires (Thoman et al. 2020).Department of Defense (DoD)