Carbon Intensity

Carbon intensity is a ratio that expresses greenhouse gas (GHG) emissions relative to a unit of output or activity. Rather than measuring total emissions in isolation, it places emissions in the context of how much was produced, sold, or consumed to generate them.

Absolute emissions measure the total volume of GHG emissions produced by a company in a given period, expressed in tonnes of carbon dioxide equivalent (CO₂e). Carbon intensity measures how many emissions are produced per unit of output: per tonne of product manufactured, per kilometre travelled, or per megawatt hour of electricity generated.

A company can reduce its carbon intensity while its absolute emissions stay flat or rise, if output grows faster than emissions. The two metrics tell different stories, and which one matters depends on the context. 

Carbon intensity appears in corporate sustainability reporting, energy system benchmarking (grid carbon intensity measures emissions per unit of electricity generated), regulatory performance standards, and product carbon footprint comparisons, where emissions are expressed per kilogram of product to enable like-for-like benchmarking.

A manufacturer produces 10,000 tonnes of steel and emits 15,000 tCO₂e in the process. Its carbon intensity is 1.5 tCO₂e per tonne of steel. If the following year it produces 12,000 tonnes and emits 16,000 tCO₂e, its absolute emissions have increased but its carbon intensity has fallen to 1.33 tCO₂e per tonne. Whether that represents progress depends on whether the goal is to reduce total emissions or to improve emissions efficiency. 

Science-based targets can be set on either an absolute or intensity basis. Intensity-based targets are accepted by the Science Based Targets initiative (SBTi) in certain sectors, but come with a condition: an intensity target does not guarantee a reduction in absolute emissions. The SBTi requires companies using intensity-based targets to demonstrate that the resulting absolute emissions trajectory is consistent with limiting warming to 1.5°C.

Carbon intensity is a useful efficiency metric, but it should always be read alongside absolute emissions data to give a complete picture of a company's climate impact.

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