"Cement accounts for around 8% of global CO₂ emissions" is one of the most repeated statistics in climate reporting. It appears in policy briefings, university lecture slides, NGO campaign pages and news articles.
The primary dataset that tracks cement emissions puts the 2024 figure at 1.47 Gt CO₂, or 3.8% of global fossil CO₂ — and shows it falling for three consecutive years.
Both numbers are defensible. They measure different things, and the difference is rarely stated. This page sets out what each one counts, gives the full series so you can check it, and explains why the direction of travel matters more than the headline share.
Every figure below is attributable. Where a number is derived rather than measured, it says so.
The measured series: cement process emissions, 1.47 Gt in 2024
These are process emissions only — the CO₂ released when limestone is chemically decomposed in the kiln. They exclude the fuel burned to heat the kiln, and they exclude everything downstream in concrete.
| Year | Cement process CO₂ (Gt) | Global fossil CO₂ (Gt) | Cement share |
|---|---|---|---|
| 2019 | 1.62 | 37.09 | 4.4% |
| 2020 | 1.62 | 35.16 | 4.6% |
| 2021 | 1.67 | 36.87 | 4.5% |
| 2022 | 1.58 | 37.53 | 4.2% |
| 2023 | 1.54 | 38.09 | 4.0% |
| 2024 | 1.47 | 38.60 | 3.8% |
Source: Global Carbon Project fossil CO₂ emissions dataset (2025v15), Andrew, R. M., & Peters, G. P. (2025), doi:10.5281/zenodo.17417124, accessed via Our World in Data. Global fossil totals from the same dataset. Percentages calculated by BisonConvey from those two series.
Two things stand out.
Cement process emissions peaked in 2021 and have fallen 11.6% since. From 1.67 Gt to 1.47 Gt in three years. Over the same period global fossil CO₂ rose from 36.87 to 38.60 Gt. Cement fell while the total climbed, so its share dropped from 4.5% to 3.8%.
The fall is not primarily a decarbonisation success. Robbie Andrew, who maintains the dataset, attributes the recent decline directly to China's property sector contraction. China produces more cement than the rest of the world combined; when Chinese construction slows, global cement emissions follow. Reading this curve as evidence that cement is decarbonising would be a mistake.
Why the 8% figure is also correct
The gap between 3.8% and 8% is not an error. It is a scope difference, and there are three common scopes:
1. Process emissions only — about 3.8%. Calcination CO₂ alone, as in the table above. This is the number in the Global Carbon Project dataset because that dataset needs a consistent, chemically-derived industrial-process category.
2. Process plus fuel — roughly 6–7%. Kiln fuel typically adds around 40% on top of process emissions, with process emissions making up the other ~60% of cement plant CO₂. Applying that split to 1.47 Gt of process emissions implies total cement-plant emissions in the region of 2.4 Gt.
This 60/40 split is widely used in the literature; the arithmetic above is ours, not a published figure.
3. The whole concrete value chain — around 8%. Adding aggregate extraction, transport, batching and construction gets to the figure most often quoted.
None of these is wrong. The problem is that they get used interchangeably, so a policy document citing "8%" and a dataset reporting "3.8%" appear to contradict each other when they simply have different boundaries. If you are citing a cement emissions figure, state the scope.
The floor set by chemistry
Process emissions have a hard lower bound that no kiln efficiency improvement can cross, and it can be derived from stoichiometry alone.
Clinker is made by decomposing calcium carbonate:
CaCO₃ → CaO + CO₂
Taking molar masses of 100.09, 56.08 and 44.01 g/mol respectively: producing 1 tonne of CaO requires 1.785 t of CaCO₃ and releases 0.785 t of CO₂. Portland cement clinker is roughly 65% CaO by mass, so:
- 1 t of clinker needs about 1.16 t of CaCO₃
- and releases about 0.51 t of CO₂ from calcination alone
Derivation by BisonConvey from standard molar masses and a nominal 65% CaO clinker composition. Actual clinker chemistry varies by plant; treat this as the order of magnitude, not a plant-specific value.
This is why cement is called hard to abate. Burning cleaner fuel, electrifying the kiln or recovering waste heat all address the other ~40% of plant emissions. None of them touch the 0.51 t/t that comes out of the limestone itself. Only two levers do: making less clinker per tonne of cement (substitution with slag, fly ash, calcined clay or limestone filler), or capturing the CO₂ at the stack.
The clinker-to-cement ratio is therefore the single most consequential number in cement decarbonisation, and it is one worth checking regionally rather than globally — reported national averages vary substantially, with North America materially higher than China.
What this means for the material moving through the plant
The stoichiometry has a physical consequence that rarely appears in emissions discussions: cement plants move far more material than they ship.
Every tonne of clinker starts as roughly 1.16 t of limestone, plus corrective materials — clay, iron, silica — to hit the target chemistry. Raw meal input per tonne of clinker is commonly in the region of 1.5–1.6 t, because calcination drives off mass as CO₂. That material has to be quarried, hauled, ground, preheated, burned, cooled, ground again with additives, and dispatched.
The 1.5–1.6 t figure is a typical industry range rather than a measured statistic; the 1.16 t limestone component is derived above.
Two implications follow, and they are the reason a conveyor manufacturer has any business writing about cement emissions at all:
Conveying is where the plant's electrical load sits, alongside grinding. A decarbonisation plan that addresses the kiln but ignores materials handling has left part of the electrical demand untouched. Belt selection, overland conveyor routing and drive efficiency are not climate interventions on the scale of clinker substitution, but they are not nothing either.
Replacing truck haulage with conveyors is a measurable local change. Quarry-to-plant limestone haulage is frequently the largest single truck movement associated with a cement works, and it is the part communities and local authorities actually experience — road wear, dust, noise, and traffic through villages. An overland conveyor removes that traffic. We have not published a per-tonne-kilometre energy comparison here because we do not have one we can source properly; if you need that comparison for a planning submission or an assessment, the honest answer is that it has to be modelled for the specific route.
If you are citing cement emissions figures
A short checklist, aimed at anyone using these numbers in a report, submission or lecture:
- State the scope. Process only, process plus fuel, or full value chain. The three differ by more than a factor of two.
- Give the year. Cement emissions have moved by over 11% in three years. A 2021 figure describes a different world from a 2024 one.
- Cite the dataset, not a secondary article. The Global Carbon Project series (doi:10.5281/zenodo.17417124) is versioned and updated annually; secondary sources often quote figures several vintages old without saying so.
- Do not read the recent decline as decarbonisation. It tracks Chinese construction demand. Clinker ratio and carbon capture are the indicators to watch for structural change.
Sources
- Andrew, R. M., & Peters, G. P. (2025). The Global Carbon Project's fossil CO₂ emissions dataset (2025v15). doi:10.5281/zenodo.17417124 — cement process emissions and global fossil totals, 1750–2024.
- Our World in Data, Annual CO₂ emissions from cement — accessible presentation of the above series.
- Andrew, R. M. Cement process emissions — dataset documentation, including the attribution of the recent decline to China's property sector.
- Stoichiometric derivations in this article are BisonConvey's own, from standard molar masses. The 60/40 process-to-fuel split and the 1.5–1.6 t raw meal range are widely used industry values presented as such, not as measured figures from a specific dataset.
Figures accurate as of the 2025v15 dataset release covering data through 2024. This page is updated when the Global Carbon Project publishes a new vintage. Corrections welcome — contact us.
Related engineering reading: Cement Plant Conveyor Design Guide covers belt selection zone by zone, including the heat-resistant belts required in clinker handling.
