Module: Decoupling
Can the economy grow while emissions fall?
Between 1990 and 2022 Canada’s real GDP grew 111% while fossil CO₂ grew 20%. That is relative decoupling. Absolute decoupling means emissions actually fall while output rises. The Kaya identity shows which forces pull each way.
- GDP, 1990–2022
- +111%
- Constant international dollars
- Fossil CO₂, 1990–2022
- +20%
- 458 → 548 Mt
- Energy used per dollar
- −38%
- Energy intensity of GDP
- CO₂ per person
- 13.4t
- 2024; peak 18.3 t in 2000
Relative decoupling: the gap between the lines
Economic output and CO₂ emissions, indexed to 1990
1990 = 100. When the lines separate, the economy is growing faster than its emissions.
- GDP (constant $)
- Fossil CO₂
The Kaya identity
An accounting identity, not a theory: it is true by definition, which makes it a clean way to sort the forces behind emissions.
The four Kaya factors, indexed to 1990
CO₂ = population × income × energy intensity × carbon intensity. Toggle factors in the legend.
Decompose any period yourself
Choose two years. The bars show how much each factor contributed to the change in emissions between them.
What drove the change in CO₂, 1990–2022?
Contribution of each factor in log points (≈ percentage points). Red pushed emissions up; blue pulled them down. The bars add up to the total.
Total change in CO₂: +17.9 log points (+19.6% from 458 Mt to 548 Mt).
How Canada compares
Fossil CO₂ per person: Canada and peers
Tonnes of CO₂ per person per year. Select a country to bring it forward.
Exercises
Why do we index both series to 1990 = 100 instead of plotting GDP in dollars and CO₂ in tonnes on the same chart?
Check your reasoning
They have different units and scales. A chart with two y-axes lets the designer choose any alignment, which can invent or hide a relationship. Indexing puts both on the same unit (percentage of a base year) so growth rates compare directly.
Run the decomposition for 1990–2005 and for 2005–2022. Which factor changed sign or size the most between the two periods?
Show a hint
Compare the income and carbon-intensity bars across the two runs.
Check your reasoning
Population pushes up by a similar amount in both periods and energy intensity falls in both. Two things changed: income per person grew far less after 2005 (about 29 log points before, 12 after, with the 2008–09 recession and the 2020 pandemic inside the window), and carbon intensity fell much faster (about −1 before, −8 after) as Ontario closed its coal plants. Together they turned a 22-point rise into a 4-point decline.
Energy intensity fell substantially. Name two different reasons this could happen and say which one a climate policy should aim for.
Check your reasoning
Efficiency gains (better engines, buildings, processes) and structural change (the economy shifting toward services that use less energy per dollar). Structural change can also mean energy-intensive production moved abroad, which reduces domestic emissions without reducing global ones; efficiency gains do not have that problem.
Explain the rebound (Jevons) effect and how it could make energy-intensity gains overstate the true emissions saving.
Check your reasoning
Efficiency lowers the effective price of energy services, so people use more of them (driving further, heating larger homes). Part of the saving is ‘taken back’. The Kaya decomposition records the net result, so it cannot by itself separate the engineering saving from the behavioural response.