Decarbonization in Shipping: Understanding the Differences Between CII and GHG

The maritime industry is going through one of the most monumental transformations in its history: Decarbonization.

However, as IMO (International Maritime Organization) regulations tighten, the industry's "alphabet soup" of jargon can easily get confusing. Two terms, in particular, are frequently mixed up: GHG (Greenhouse Gas) targets and CII (Carbon Intensity Indicator) ratings.

So, what exactly is the fundamental difference between these two concepts?

GHG vs. CII: What’s the Core Difference?

To put it simply: GHG is the big picture, while CII is the annual performance grade your ship receives for contributing to that picture.

• GHG (Greenhouse Gas) Target: This refers to the total emissions originating from global shipping. The IMO’s revised greenhouse gas strategy aims to reach net-zero GHG emissions by or around 2050. The main focus here is the reduction of absolute emissions.

• CII (Carbon Intensity Indicator): This is a system that measures a ship's operational efficiency. It calculates how much CO2 a vessel emits per unit of transport capacity and distance traveled. Ships are graded annually on a scale from A (best) to E (worst).

The Bottom Line: GHG emissions are the actual enemy we need to defeat; CII is the grade your ship gets on the battlefield.

CII Improvement Strategies for Ships

Keeping your CII rating high (A or B) is critical for maintaining your vessel's commercial value. Achieving this usually requires short- to medium-term operational interventions:

• Speed Optimization (Slow Steaming): Strategically reducing vessel speed to significantly lower fuel consumption.

• Route and Weather Optimization: Planning the most fuel-efficient route by utilizing real-time wind and ocean current data.

• Hull and Propeller Cleaning: Removing biofouling to reduce hydrodynamic drag, thereby easing the load on the engine.

• Energy Saving Devices (ESDs): Integrating innovative technologies such as air lubrication systems or wind-assisted propulsion.

  
  

Long-Term GHG Reduction Strategies

Reaching net-zero targets goes beyond operational tweaks; it requires massive, structural changes:

• Transitioning to Alternative Fuels: Adopting low- or zero-carbon fuels such as LNG (as a transition fuel), methanol, ammonia, or green hydrogen.

• Fleet Renewal: Phasing out older, inefficient vessels and replacing them with a new generation of highly energy-efficient ships.

• Carbon Capture Systems (CCS): Installing onboard technology to capture and store emissions before they can escape into the atmosphere.

  
  

At a Glance: GHG vs. CII Comparison Table

To break it down even further, here is a quick reference guide showing exactly how GHG and CII differ:

Feature	GHG (Greenhouse Gas)	IMO CII (Carbon Intensity Indicator)
Concept Type	Scientific and environmental term (Physical gases).	Regulatory and mathematical metric (Performance grade).
Definition	Gases that trap heat in the atmosphere, causing global warming.	An efficiency system measuring CO2 emitted relative to cargo carried and distance traveled.
Measurement Unit	Total emission volume (e.g., Million tons of CO2 equivalent).	Proportional efficiency rating.
Scope	Covers emissions in nature and across all industries (aviation, road transport, agriculture, etc.).	Strictly applies to internationally trading commercial ships of 5,000 GT and above.
Primary Goal	To prevent global warming and halt climate change.	To force ships to operate more efficiently, thereby lowering GHG emissions.