What Is Carbon Intensity?

Carbon intensity is a measure of how much carbon dioxide is released for each unit of electricity produced. It is written in grams of CO2 per kilowatt hour, shortened to gCO2/kWh, so a grid running at 400 gCO2/kWh puts out 400 grams of CO2 for every kilowatt hour it generates. It tells you how clean the electricity is, not how much of it there is.

How the number is built

Carbon intensity is an average, not a property of any single power station. You take the emissions from every generator on a grid over some period, add them up, and divide by the electricity those generators produced in the same period. A grid that runs mostly on coal lands high, because coal plants emit a lot per kilowatt hour. A grid that runs mostly on hydro, nuclear, wind or solar lands low, because those sources emit little or nothing while they operate.

Because it is an average, the number moves whenever the mix moves. Add solar and the intensity falls. Lose a nuclear plant to maintenance and burn gas instead, and it rises. Cold, still, dark weather in a wind heavy system can push the figure up for days at a time, then a windy week pushes it back down. Annual figures hide all of that variation inside one number, which is the price of having a figure that is comparable between countries and across decades.

Lifecycle emissions versus direct emissions

There are two common ways to count the emissions, and they give different answers.

Direct emissions, sometimes called combustion, operational or stack emissions, count only the CO2 released when fuel is burned. On this measure nuclear, wind, solar and hydro are zero, because nothing is burned.

Lifecycle emissions count the whole chain: mining and processing the fuel, transporting it, manufacturing the turbines or panels, building and eventually dismantling the plant. On this measure nothing is zero. Wind and nuclear come out very low, solar a little higher because of the energy used to make the panels, and fossil fuels higher still than their direct emissions alone, partly because coal mining and gas production leak methane before the fuel ever reaches a power station.

Neither method is wrong. They answer different questions. Direct emissions tell you what a country’s power sector is emitting inside its own borders this year, which is what national inventories are built on. Lifecycle emissions tell you the full climate cost of choosing one technology over another, including emissions that happen in other countries and in other years.

The practical consequence is that you cannot compare a lifecycle figure with a direct figure and draw a conclusion. If one source says a country is at 250 gCO2/kWh and another says 300, the gap may be entirely a matter of what was counted.

Why intensity and total emissions tell different stories

Intensity is a rate. Total emissions are a quantity. Confusing the two produces some very wrong conclusions.

Take two countries from Ember’s 2025 statistics. France had a carbon intensity of about 41 gCO2/kWh, one of the lowest of any large system, and its power sector emitted roughly 24 million tonnes of CO2 that year. India had a carbon intensity of about 671 gCO2/kWh, and its power sector emitted roughly 1,400 million tonnes. India’s intensity is about sixteen times France’s, but its total emissions are about sixty times larger, because India generates several times more electricity.

The reverse case matters too. A country can cut its intensity every year while its total emissions rise, if demand grows faster than the mix cleans up. Ember’s figures show exactly that pattern at the world level: global carbon intensity fell from about 527 gCO2/kWh in 2000 to about 459 gCO2/kWh in 2025, yet total power sector emissions were much higher at the end of that period than at the start, because world generation roughly doubled.

So intensity is the right measure for asking “how clean is a kilowatt hour here”, and total emissions are the right measure for asking “how much is this country adding to the atmosphere”. Use both.

What moves a grid’s carbon intensity

• The generation mix. This dominates everything else. The share of coal is usually the single strongest predictor.
• Plant efficiency. A modern combined cycle gas plant emits far less per kilowatt hour than an old open cycle unit burning the same fuel.
• Demand shape. Peak hours are often met by the least efficient plants kept in reserve, so intensity is usually higher at peak than overnight.
• Weather. Rainfall sets how much hydro is available. Wind and sunshine set how much of the demand is met without fuel.
• Imports and exports. Electricity crossing a border carries emissions that were produced somewhere else. Most published country figures are based on generation inside the country, so a country importing clean power from a neighbour does not always get credit for it in the headline number.

How World Power Monitor shows carbon intensity

Our carbon intensity pages show Ember’s annual figures for every country we cover. Three things are worth knowing about them.

First, they are lifecycle based. Ember applies its own emission factors to each fuel, and those factors include upstream emissions, so the figures sit above a direct emissions count for the same country and year.

Second, they are annual averages tied to a stated year. They are not a live reading, and we never present them under a “right now” heading. When you see a figure on this site it comes with the year it describes.

Third, they are comparable across countries because they come from one compiler using one method. That is the main reason we use a single source for country statistics rather than stitching national publications together. It also means our numbers will not match every national figure exactly, and they are not meant to.

Where grid operators publish enough detail, a live carbon intensity can be estimated from the mix of fuels running at that moment. Those estimates use a different method from Ember’s annual statistics, so they are shown separately and labelled as estimates. Comparing the two as if they were the same measure would be a mistake.

Reading intensity figures sensibly

A single annual number is a summary, and summaries lose information. Two grids can share an average of 300 gCO2/kWh while one sits steadily around that level all year and the other swings between 60 and 700 depending on the wind. For someone deciding when to charge a car or run a heat pump, the swing matters more than the average. For someone comparing national progress over twenty years, the average is exactly the right tool.

When you see a carbon intensity figure anywhere, ask three questions: which year does it cover, does it count lifecycle or direct emissions, and is it measuring generation inside the territory or the electricity actually consumed there. With those three answers, the number means something. Without them, it is just a number.