Ship Emissions Calculator

Maritime emissions accounting is fuel-based rather than measured at the stack. Because marine engines burn fuel close to completely, the carbon in the bunker tank is a reliable proxy for the carbon leaving the funnel, so total CO2 is simply tonnes of fuel consumed multiplied by a carbon factor fixed by fuel chemistry. Those factors are near 3.114 for heavy fuel oil, 3.206 for marine diesel oil, about 3.151 for very low sulfur fuel oil, roughly 2.75 for LNG and around 1.375 for methanol, the last two being lower because of higher hydrogen content or partial oxidation of the carbon in the molecule. Sulfur oxide output scales directly with the sulfur specification of the fuel, whereas nitrogen oxides depend on combustion temperature and engine design rather than fuel carbon, which is why a fuel switch cuts SOx to zero while barely moving NOx. Voyage fuel here is derived from daily consumption multiplied by voyage days, with days taken as distance divided by speed. That linearity conceals the strongest lever in ship operations: hull resistance rises steeply with speed, so consumption per day scales roughly with the cube of speed and fuel per mile with the square. Cutting speed by 10 percent therefore removes on the order of a quarter of the fuel burn for that leg. The efficiency outputs express intensity rather than total: the Energy Efficiency Operational Indicator gives grams of CO2 per tonne-nautical mile of cargo actually moved, so a half-empty ship rates poorly regardless of engine quality. Ballast legs, weather routing, hull fouling and auxiliary and boiler load are not captured, and the letter grade shown is an approximation of the regulatory Carbon Intensity Indicator, not a certified rating.

Air emissions from ships were largely unregulated until MARPOL Annex VI was adopted by the International Maritime Organization in 1997; it entered into force in 2005 and set the first global caps on sulfur oxides and nitrogen oxides, along with the framework for designating stricter Emission Control Areas such as the Baltic and North Sea and later the North American coast. Greenhouse gases were addressed separately and later, through a series of IMO studies, the first in 2000 and the fourth in 2020, which put international shipping at roughly 3 percent of global anthropogenic CO2. Operational metrics arrived alongside. The IMO issued guidelines for the voluntary Energy Efficiency Operational Indicator in 2009. In July 2011 the Marine Environment Protection Committee adopted the Energy Efficiency Design Index for new ships together with the mandatory Ship Energy Efficiency Management Plan, effective from January 2013, making shipping the first international transport sector with binding efficiency requirements. The European Union added its Monitoring, Reporting and Verification regulation in 2015, and the global 0.50 percent sulfur cap, widely called IMO 2020, took effect on 1 January 2020, displacing high sulfur residual fuel except on scrubber-fitted vessels. The Carbon Intensity Indicator and the Energy Efficiency Existing Ship Index were adopted in 2021 and applied from 2023, and the IMO revised greenhouse gas strategy agreed in 2023 set an ambition of net-zero emissions by or around 2050 with interim checkpoints.