Carbon intensity, often shortened to CI, is a score for how much greenhouse gas a fuel is responsible for across its whole life, measured per unit of energy the fuel delivers.
Greenhouse gases are the gases, carbon dioxide chief among them, that trap heat and drive climate change. Carbon intensity measures how much of those gases a fuel causes, counted from the start of making it through to burning it. The score is set per unit of energy, so a gallon of one fuel and a gallon of another can be compared fairly even if they pack different amounts of energy.
Because it covers the whole life of the fuel, CI counts far more than the tailpipe. It includes growing or drilling the raw material, refining or processing it, and hauling it to where it is used. Two fuels that burn the same in an engine can carry very different CI scores depending on how each one was made and moved.
In clean-fuel programs, CI is the number that matters. A program sets a yearly target CI for transportation fuel, and each fuel is scored against it. A fuel below the target counts as clean and earns credits, while one above the target runs up deficits the seller has to cover.
For a fuel marketer or jobber, CI turns an environmental idea into a business number. A lower-CI fuel can be worth real money through the credits it earns in states that run these programs, so knowing the score of what you sell is part of knowing your margin.
In useA renewable diesel made from used cooking oil usually scores a much lower carbon intensity than ordinary diesel, so in a clean-fuels state it earns credits instead of running up deficits.
See also Lifecycle greenhouse gas emissions, Low Carbon Fuel Standard (LCFS), Fuel pathway