Open IMO Carbon Intensity Indicator (CII) Calculator (Python) 🚢

Other versions

A C# version is available here

A web version of this repository is available at www.121-export.com

What is this?

An unofficial open source implementation of the International Maritime Organisation (IMO)'s Carbon Intensity Indicator (CII).

The CII indicator aims to make the carbon intensity of any given ship easy to understand, transparent, and standardised. It does so by ranking all ships globally on an A to E rating (A being the best, E being the worst). Ship emission intensity calculations consider a mixture of weight, distance travelled in the calendar year, and the fuel used in their main engines (for a comprehensive explanation, see the methodology section).

Grades are re-calculated annually. The boundaries of what is considered "good" is a moving target, described in table 4. This moving target is intended to encourage shipping firms to constantly improve the carbon intensity of their ships to 2030. The graph below demonstrates the gradual tightening of the IMO's Carbon Intensity requirements over time. The nearer to 2030, the lower a ship's Attained CII must be to achieve an A grade.

The specification for this software can be found in IMO's resolution MEPC.354(78), adopted in June 2022. Additional references, summaries, & resolutions can be found in the References & datasets section.

NOTE The repository code & software is provided as-is. While best-efforts are made to ensure its results are accurate inline with the IMO's CII specifications, the results it produces are estimates and guidance. Results should not be considered proof of regulatory compliance.

Table of Contents

• Open IMO Carbon Intensity Indicator (CII) Calculator 🚢
  • What is this?
• Table of Contents
• Software
  • Software Roadmap
  • Getting Started
    • Calculator Result Format
• Methodology
  • Ship Grade Ratio Methodology
    • Ship Grade Worked example
  • Ship Attained Carbon Intensity Methodology
  • Ship transport work methodology
  • Ship CO2 Emissions Methodology
  • Ship Capacity Methodology
• Reference Tables
  • Table 1: MEPC.353(78) - Shipping Capacity Tables
  • Table 2: MEPC.364(79) Mass Conversion between fuel consumption and CO2 emissions
  • Table 3: MEPC.339(76) - Ship Grading Boundaries
  • Table 4: Annual Carbon Reduction Factors (Z%)
  • Table 5: Common shipping measurement conversions
• Shipping Terminology & Glossary
• References & datasets
  • Further Reading
  • Useful datasets (mixed public and private)

Software

Running tests

To run the unit tests for this Python implementation, use the following command from the ./open_imo_cii_calculator directory:

poetry install
poetry run pytest

This will automatically discover and run all tests in the tests/ directory.

Software Roadmap

The following features are on the roadmap for the application:

• Support for Dependency Injection (DI). Currently the application does not
• Support for IMO Resolution MEPC.355(78). Currently the application considers fuel consumption only. Support for MEPC355(78) will bring additional CII properties, for example the lighting in crew quarters.

Getting Started

The library can be installed as a Python package (coming soon). There is a Python module at open_imo_cii_calculator/ship_carbon_intensity_calculator.py, which demonstrates how to create a new instance of the calculator, submit data, and receive results in the format CalculationResult.

When submitting data to the calculate_attained_cii_rating method, the following parameters are required:

ShipType ship_type,
float gross_tonnage,
float deadweight_tonnage,
float distance_travelled,
Iterable[FuelTypeConsumption] fuel_type_consumptions,
int target_year

• The ship's type must be one of ShipType (see open_imo_cii_calculator/models/ship_type.py).
• Gross Tonnage is measured in long-tons (1.016047 metric tonnes, or 1,016.047 kilograms)
• Deadweight Tonnage is measured in long-tons (1.016047 metric tonnes, or 1,016.047 kilograms)
• Distance travelled is measured in nautical miles (1,852 metres)
• Fuel type must be one of TypeOfFuel (see open_imo_cii_calculator/models/fuel_type.py)
• Fuel consumption is measured in grams, and accepts scientific notation like 1.9e+10
• Year must refer to the measured year. For example, if a ship's fuel consumption is known in 2022, all other results will be based from that point

Multiple Fuel Type calculations

There is a calculate_attained_cii_rating method for ships which consume multiple fuel types. Pass a list of FuelTypeConsumption objects to the method.

Calculator Result Format

The result is a CalculationResult object containing a list of ResultYear objects, each with the following properties:

• is_measured_year: describes if the result array was generated based on this year
• is_estimated_year: describes if the result array was NOT generated based on this year (is always equal to not is_measured_year)
• year: describes the year in question
• rating: describes the rating for the ship in the given year. A=1, B=2, C=3, D=4, E=5. 0 indicates an error. See ImoCiiRating in open_imo_cii_calculator/models/imo_cii_rating.py
• required_cii: The actual intensity required for the ship to be considered in-range of the IMO's regulations (note that from 2027 onwards, this is a projection)
• attained_cii: The estimated or actual intensity attained for the ship in the given year
• attained_required_ratio: The ratio between required_cii and attained_cii
• calculated_co2e_emissions: The calculated CO2e emissions this result was based on
• calculated_ship_capacity: The calculated ship capacity this result was based on
• calculated_transport_work: The calculated transport work this result was based on
• vector_boundaries_for_year: An object with the following properties:
  • year: the year in question
  • ship_type: the type of ship (ShipType)
  • weight_classification: the weight classification the ship has been considered for
  • capacity_unit: describes if this ship was measured against its Deadweight or Gross Tonnage (CapacityUnit)
  • boundary_dd_vectors: a dictionary with keys SUPERIOR, LOWER, UPPER, INFERIOR (see ImoCiiBoundary)

Methodology

A ship's Carbon Intensity Indicator (CII) is measured by calculating its transport workload in a given calendar year, then calculating the mass of $CO_2$ produced by the ship in that year. The ship's Attained CII is the product of its $transportWork$ and the $massOfCO_2Emissions$ in one calendar year.

$AttainedCII = massOfCo2Emissions / transportWork$

Ships are split into 12 categories, for example "Bulk Carrier", "Tanker", "Cruise Passenger Ship" among others (see Table 1 for a comprehensive list). A ship is compared internally among its category peers but never across categories, for example, a Bulk Carrier is not directly comparable to a LNG Carrier in this system.

Inputs

• The type of ship
• The type of fuel used by the ship's main engine
• The capacity of the ship, measured in either Deadweight Tonnage (DWT) or Gross Tonnage (GT)
• The distance travelled by the ship in one calendar year, measured in nautical miles

The ship's Attained CII is then compared to its Required CII to produce an easy to understand grade for the ship. The grading scheme is in the range A to E, where A is the most efficient bracket, C represents a ship at-or-near its CII, and E is the least efficient.

Grade	Description
A	CII below the Superior Boundary
B	CII above the Superior Boundary and below the Lower Boundary
C	CII between the Lower Boundary and the Upper Boundary
D	CII above the Upper Boundary and below the Inferior Boundary
E	CII above the Inferior Boundary

Fig1. IMO Boundaries, after IMO MEPC.354(78)

Ship Grade Ratio Methodology

A ship's grade is calculated by comparing its Attained CII to its Required CII to give its performance $A/R$ ratio. If the ship's $A/R$ ratio falls below the boundary for its class of Ship Type, it attains a higher (better) grade. Boundaries are calculated as:

$shipTypeRequiredCII \times exp(d_i)$.

Ship Grade Worked example

The worked example below considers a Bulk Carrier, with a Deadweight Tonnage below 279,000. Assuming the Bulk Carrier's $required CII$ is:

$10g CO_2 / DWT.NM$

IMPORTANT For some ship types, $GT \times NM$ should be used instead of $DWT \times NM$, see Table 1 and transport work done methodology for a comprehensive guide.

Then the boundaries are calculated with:

• $10 \times exp(d1)$
• $10 \times exp(d2)$
• $10 \times exp(d3)$
• $10 \times exp(d4)$.

The $exp(d_i)$ rating boundaries for each ship type can be found in Table 3. The resultant boundaries for the Bulk Carrier in question are:

Boundary Type	Required CII	Boundary's Lower Threshold
Superior	$= 10 \times exp(d1)$ $= 10 \times 0.86$ $= 8.6$	$8.6 gCO_2/transportWork$
Lower	$= 10 \times exp(d2)$ $= 10 \times 0.94$ $= 9.4$	$9.4 gCO_2/transportWork$
Upper	$= 10 \times exp(d3)$ $= 10 \times 1.06$ $= 10.6$	$10.6 gCO_2/transportWork$
Inferior	$= 10 \times exp(d4)$ $= 10 \times 1.18$ $= 11.8$	$11.8 gCO_2/transportWork$

Grades are then derived from these boundaries, by comparing the ship's Attained CII to the thresholds across a given calendar year:

Grade	Higher than	Lower than	Description
A		8.6	Below Superior Boundary
B	8.6	9.4	Above Superior Boundary, Below Lower Boundary
C	9.4	10.6	Above Lower Boundary, Below Upper Boundary
D	10.6	11.8	Above Upper Boundary, Below Inferior Boundary
E	11.8		Above Inferior Boundary

Example Results:

• If the ship's Attained CII was $9gCO_2/ DWT \times NM$, the ship receives a grade B, as its Attained CII was above the threshold for Superior Boundary, but below the threshold for Lower Boundary.
• If the ship's Attained CII was $11gCO_2/ DWT \times NM$, the ship receives a grade D, as its Attained CII was above the threshold for Upper Boundary, but below the threshold for Inferior Boundary.

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Ship Attained Carbon Intensity Methodology

A ship's Attained carbon intensity is calculated by taking the mass of its aggregate CO₂ emissions in a calendar year, and dividing it by its transport work done in the calendar year.

$AttainedCII = massOfCo2Emissions / transportWork$

Method accepts:

• mass_of_co2_emissions, the mass of $CO_2$ emissions in the calendar year
  • See co2 emissions methodology to calculate
• transport_work, the work carried out by the ship in the calendar year
  • See transport work methodology to calculate

Method Returns:

• A float representing the ship's Attained Carbon Intensity

Implementation:

Returns the quotient of a ship's mass of $CO_2$ emissions and its $transportWork$.

Ship transport work methodology

A ship's transport work is calculated by taking its capacity and multiplying it by the distance sailed in nautical miles in the calendar year.

$capacity \times distanceSailed$

Method accepts:

• capacity the ship's capacity for cargo or passengers
  • See ship capacity methodology to calculate
• distance_sailed the distance sailed in Nautical Miles in the calendar year

Implementation:

Returns the product of a ship's capacity and its distance sailed

Ship CO₂ Emissions Methodology

The sum of a ship's $CO_2$ emissions over a given year are calculated by multiplying the mass of consumed fuel by the fuel's emissions factor. If the ship consumes multiple fuel types, the calculation is repeated for each fuel type & consumption mass, then those results are summed together.

Method Accepts:

• fuel_type, an enum derived from Table 2's Fuel Type column
• fuel_consumption_mass, a float representing the mass of fuel consumed in grams (g) over the given year

Method Returns:

• A float representing the $M$ mass of $CO_2$ emitted by the ship across one calendar year

Implementation:

The sum of $CO_2$ emissions $M$ from fuel consumption in a given calendar year is

$M = FC_j \times C_{{f_j}}$

Where:

• $j$ is the fuel type
• $FC_j$ is the mass in grams of the consumed fuel type j in one calendar year
• $C_{{f_j}}$ is the fuel oil mass to CO2 mass conversion factor, given in Table 2's $C_F$ column

Ship Capacity Methodology

A ship's capacity is measured by either its Deadweight Tonnage (DWT) or Gross Tonnage (GT). The only exception is Bulk Carriers, which have a capacity capped at 279,000.

To calculate a ship's Capacity in accordance with the IMO's MEPC353(78) guidelines:

Method accepts:

• ship_type, an enum, derived from Table 1's Ship Type column
• deadweight_tonnage, the deadweight tonnage of the ship, provided in long tons
• gross_tonnage, the gross tonnage of the ship, provided in long tons

Method returns:

• a float representing the ship's capacity in imperial long tons

Implementation:

$Capacity$ of a given ship is calculated using the following rules:

• If the ship is a Bulk Carrier, and its DWT is 279,000 or above, its capacity is capped at 279,000
• If the ship is a Bulk Carrier, and its DWT is below 279,000, its capacity is equal to its DWT
• If the ship is a Ro-ro cargo ship (vehicle carrier), a Ro-ro passenger ship or a Cruise passenger ship, its capacity is equal to its Gross Tonnage
• Otherwise, the ships capacity is equal to its DWT

The full implementation detail can be found in Table 1's Ship Type, Ship weight, and Capacity columns.

Exceptions:

• ValueError is raised if the DWT is set to 0, when ship type is set to anything other than Ro-ro cargo ship (vehicle carrier), Ro-ro passenger ship or Cruise passenger ship
• ValueError is raised if the GT is set to 0, when ship type is set to Ro-ro cargo ship (vehicle carrier), Ro-ro passenger ship or Cruise passenger ship

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Reference Tables

Table 1: MEPC.353(78) - Shipping Capacity Tables

The following table describes how to determine a given ship type's Capacity.

Table Source: IMO: MEPC.353(78)

Ship Type	Conditional Specification	Capacity	$a$	$c$
Bulk carrier	279,000 DWT and above	279,000	4,745	0.622
Bulk carrier	Less than 279,000 DWT	DWT	4,745	0.622
Gas carrier	65,000 and above	DWT	14405E7	2.071
Gas carrier	Less than 65,000 DWT	DWT	8,104	0.639
Tanker		DWT	5,247	0.610
Container Ship		DWT	1,984	0.489
General cargo ship	20,000 DWT and above	DWT	31,948	0.792
General cargo ship	Less than 20,000 DWT	DWT	588	0.3885
Refrigerated cargo carrier		DWT	4,600	0.557
Combination carrier		DWT	5,119	0.622
LNG Carrier	100,000 DWT and above	DWT	9.827	0.000
LNG Carrier	65,000 and above, less than 100,000	DWT	14479E10	2.673
LNG Carrier	less than 65,000 DWT	DWT	14779E10	2.673
Ro-ro cargo ship (vehicle carrier)	57,700 and above	57,000	3,627	0.590
Ro-ro cargo ship (vehicle carrier)	30,000 and above, less than 57,700	3627	5,739	0.590
Ro-ro cargo ship (vehicle carrier)	less than 30,000	GT	330	0.329
Ro-ro cargo ship		GT	1,967	0.485
Ro-ro passenger ship	Ro-ro passenger ship	GT	2,023	0.460
Ro-ro passenger ship	High-speed craft designed to SOLAS chapter X	GT	4,196	0.460
Cruise passenger ship		GT	930	0.383

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Table 2: MEPC.364(79) Mass Conversion between fuel consumption and CO₂ emissions

The following table describes how to convert from the fuel used by a ship's main engine $ME_{{(i)}}$ to the amount of $CO_2$ produced. Fuel consumption is measured in grams (g), as is the output $CO_2$ emission

Table source: IMO: MEPC.364(79)

ID	Fuel Type	Source/Reference	Carbon Content	$C_F (\frac{t-CO_2}{t-Fuel})$	Lower calorific value (kJ/kg)
1	Diesel / Gas Oil	ISO 8217 Grade DMX to DMB	0.8744	3.206	42,700
2	Light Fuel Oil (LFO)	ISO 8217 Grade RMA to RMD	0.8594	3.151	41,200
3	Heavy Fuel Oil (HFO)	ISO 8217 Grade RME to RMK	0.8493	3.114	40,200
4a	Liquified Petroleum (Propane)	Propane	0.8182	3.000	46,300
4b	Liquified Petroleum (Butane)	Butane	0.8264	3.030	45,700
5	Ethane	-	0.7989	2.927	46,400
6	Liquified Natural Gas (LNG)	n/a	0.7500	2.750	48,000
7	Methanol	n/a	0.3750	1.375	19,900
8	Ethanol	n/a	0.5217	1.913	26,800

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Table 3: MEPC.339(76) - Ship Grading Boundaries

The following table describes the $dd$ vectors used to determine the rating boundaries for ship types. The columns $dd$ $exp(d_i)$ values represent the boundaries the IMO's rating system in the baseline year (2019).

Table source (2022): IMO: MEPC.354(78) Previous source (2021): IMO: MEPC.339(76)

Id	Ship Type	Weight Classification	Capacity in CII Calculation	dd vector exp(d1)	dd vector exp(d2)	dd vector exp(d3)	dd vector exp(d4)
1	Bulk Carrier		DWT	0.86	0.94	1.06	1.18
2.a	Gas Carrier	65,000 DWT and above	DWT	0.81	0.91	1.12	1.44
2.b	Gas Carrier	Less than 65,000 DWT	DWT	0.85	0.95	1.06	1.25
3	Tanker		DWT	0.82	0.93	1.08	1.28
4	Container Ship		DWT	0.83	0.94	1.07	1.19
5	General Cargo Ship		DWT	0.83	0.94	1.06	1.19
6	Refrigerated Cargo Carrier		DWT	0.78	0.91	1.07	1.20
7	Combination Carrier		DWT	0.87	0.96	1.06	1.14
8.a	LNG Carrier	100,000 DWT and above	DWT	0.89	0.98	1.06	1.13
8.b	LNG Carrier	Less than 100,000 DWT	DWT	0.78	0.92	1.10	1.37
9	Ro-ro Cargo Ship (Vehicle Carrier)		GT	0.86	0.94	1.06	1.16
10	Ro-ro Cargo Ship		GT	0.76	0.89	1.08	1.27
11	Ro-ro Passenger Ship		GT	0.76	0.92	1.14	1.30
12	Cruise Passenger Ship		GT	0.87	0.95	1.06	1.16

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Table 4: Annual Carbon Reduction Factors (Z%)

The following table describes the reduction factor to be applied to a ship's $requiredCII$ on an annual basis. IMO have to date released figures up to 2026. In the table, the values from 2027 onwards are unofficial estimates based on the pattern to 2026. IMO aims to release new reduction factors

Table Source: IMO: MEPC.338(76)

Year	Reduction factor Relative to 2019	Estimated Reduction Factor
2019	0%	-- %
2020	1%	-- %
2021	2%	-- %
2022	3%	-- %
2023	5%	-- %
2024	7%	-- %
2025	9%	-- %
2026	11%	-- %
2027	-- %	13%
2028	-- %	15%
2029	-- %	17%
2030	-- %	19%

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Table 5: Common shipping measurement conversions

Often in shipping, non-metric measurements are used. Conversions are detailed below

Measure	Metric Measure	Notes
Deadweight Tonne (DWT)	$1016.0469088kg$	DWT is a ship's total weight excluding boiler water, measured in Imperial long tons
Gross Tonne (GT)	$1016.0469088kg$	GT is a ship's area, measured in Imperial long tons
Nautical Mile (NM)	$1.852km$, $1,852m$	NM is equal to 1 minute of latitude at the equator. $1NM = 1.5078 miles = 1.852km$

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Shipping Terminology & Glossary

Term	Description	Notes
Carbon Dioxide Equivalent (CO2eq, CO2, CO2e, $CO_2$)	A ship's carbon dioxide emissions	Expressed in this implementation in grams (metric)
Carbon Intensity Index (CII)	The relative measure of a ship's carbon dioxide emissions, taking distance travelled and fuel type used into account
Deadweight Tonnage (DWT)	The measure of a the total contents of a ship, including cargo, fuel, crew, passengers, and water (Excludes water in a ship's boiler)	Expressed in long tons (British Imperial)
Final Draft International Standard (FDIS)	A draft status for an ISO Standard, indicating the standard is in its final stage of approval
Gross Tonnage (GT)	A ship's internal volume	Expressed in long tons (British Imperial)
International Maritime Organisation (IMO)	A UN Agency responsible for regulating maritime transport rules & regulations
International Organization for Standardization (ISO)	Independent, non-governmental, international standard development organization
Liquefied natural gas (LNG)	Gas, compressed into liquid form for easier transport
Nautical Miles (NM, nmile)	Distance travelled over water, different to land measured miles (statute miles)	Expressed in minutes of latitude at the equator
Resolution MEPC.353(78)	Internationally standardised reference guide to shipping carbon intensity
Roll-on-roll-off (Ro-ro, Roro, Ro ro)	A ship designed to take cargo which can be wheeled (or rolled) in and out of a cargo hold

References & datasets

• IMO: MEPC.337(76) - Carbon Intensity Index (CII) spec: https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.337(76).pdf
• IMO: MEPC.364(79) - Energy Efficiency Design Index (EEDI) spec: https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.364(79).pdf
• IMO: MEPC.339(76) - 2021 Guidelines on the operational carbon intensity rating of ships (CII Rating Guidelines, G4): https://wwwcdn.imo.org/localresources/en/OurWork/Environment/Documents/Air%20pollution/MEPC.339(76).pdf
• IMO: MEPC.339(76) - 2022 Guidelines on the operational carbon intensity rating of ships (CII Rating Guidelines, G4): https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.354(78).pdf
• ISO 8217:2017 (Current standard) - Petroleum products, Fuels (class F), Specifications of marine fuels: https://www.iso.org/standard/64247.html
• ISO/FDIS 8217 (Standard under development) - Products from petroleum, synthetic and renewable sources, Fuels (class F), Specifications of marine fuel: https://www.iso.org/standard/80579.html

Further Reading

• IMO's press briefing, including links to the comprehensive guidelines: https://www.imo.org/en/MediaCentre/PressBriefings/pages/CII-and-EEXI-entry-into-force.aspx
• Society of Naval Architecture Students summary of CII Calculations: https://github.com/snascusat/CII-Calculator
• DNV's summary of EEXI and CII requirements: https://www.dnv.com/news/eexi-and-cii-requirements-taking-effect-from-1-january-2023-237817/

Useful datasets (mixed public and private)

• UNStats (public, non-commercial dataset): https://unstats.un.org/bigdata/task-teams/ttt-dashboards/
• Dataliastic (private commercial dataset): https://datalastic.com/pricing/
• Marine Traffic (private commercial dataset): https://servicedocs.marinetraffic.com/
• Windward.AI (private commercial datasets): https://windward.ai/