# Energy transitions and climate: Why transitions are slow

Source page: https://www.materialinsights.org/learn/energy/energy-transitions-climate/p2/

[Understanding Energy](https://www.materialinsights.org/learn/energy/) / [Module 13: Energy transitions and climate](https://www.materialinsights.org/learn/energy/energy-transitions-climate/) Part 2 of 4

## Why transitions are slow

If solar power now gives the cheapest new electricity in much of the world, why do fossil fuels still supply most energy? The answer lies in the sheer size of the system, the long lives of its machines, the way fuels, converters and networks are bolted together, and the stubborn fact that demand keeps rising. Each of these slows change, however cheap the new technology.

### 2.1 The fossil system is the largest machine humanity has built

Start with scale. The world now emits about 38 billion tonnes of CO2 a year from fossil fuels and cement, according to the Global Carbon Budget's estimate for 2025, which corresponds to roughly 10 billion tonnes of carbon. Behind that figure stand thousands of coal mines and oil and gas fields, hundreds of refineries, hundreds of thousands of kilometres of pipelines, thousands of power stations, more than a billion road vehicles, tens of thousands of ships and aircraft, and billions of boilers, furnaces and stoves.

Smil's point is not that this system cannot change, but that any replacement has to be built at a comparable scale. A technology that grows 50-fold from a tiny base can still be small next to a system this big. Between 2000 and about 2020, new renewables (wind, solar and modern biofuels) grew roughly 50 times over, yet the fossil share of world primary energy slipped only from about 87% to about 85%, and much of that slippage came from more hydroelectricity.

Scale also shows up in materials. Wind turbines, solar farms, transmission lines and batteries need steel, concrete, copper, aluminium, glass, silicon and battery minerals in large quantities. Most of those materials are still produced with fossil energy, so the new system is being built with the old one. That is not a contradiction; every transition has worked this way, and early railways ran on iron smelted with charcoal and rails laid by horse-drawn carts. But it means the build-out has its own emissions and its own supply constraints, including the concentration of mineral processing in a few countries.

The practical lesson for anyone assessing a plan is to translate it into physical quantities. How many gigawatts a year, how many tonnes of steel and copper, how many kilometres of line, how many trained workers? If the implied build rate is many times anything achieved before, the plan needs a very good explanation of what will be different this time.
 In the data

#### From CO2 to carbon, and a sense of scale

The Global Carbon Budget projected fossil CO2 emissions at a record 38.1 Gt in 2025, up 1.1% on 2024. Multiplying by 12/44, the share of a CO2 molecule's mass that is carbon, gives about 10.4 Gt of carbon. Adding 4.1 Gt of CO2 from land-use change, mostly deforestation, brings humanity's total to more than 42 Gt of CO2. For comparison, world crude oil output is a little under 5 Gt a year, so the CO2 we release weighs roughly eight times as much as all the oil we pump.

- Smil, How the World Really Works: A Scientist's Guide to Our Past, Present and Future (2022) · via Smil Mastery Course, M9 'Why transitions are slow'
- Smil, Energy Transitions: Global and National Perspectives (2017) · via Smil Mastery Course, M9 'Why transitions are slow'
- Global Carbon Project, Global Carbon Budget 2025 (November 2025) · 'Fossil fuel CO2 emissions hit record high in 2025', https://globalcarbonbudget.org/fossil-fuel-co2-emissions-hit-record-high-in-2025/

### 2.2 Long-lived assets and locked-in networks resist early retirement

Energy assets are built to last. Coal and nuclear stations run for 40 to 60 years, hydro dams for a century, refineries and pipelines for decades, and buildings, which set much of the demand for heating and cooling, for a century or more. A car lasts 15 years or so, an industrial boiler 30. When a coal plant is closed after 15 years, its owner writes off most of the capital, and somebody, often electricity consumers or taxpayers, pays for it.

This bites hardest in fast-growing economies. A large part of the coal fleet in China and India was built in the past two decades, so on normal lifetimes much of it could run into the 2050s or 2060s. Closing it early, or running it for fewer hours as backup to renewables, raises hard questions of finance and fairness: who compensates the owners, the lenders, the workers and the coal-mining regions?

The second source of inertia is lock-in. Fuels only work with matching converters, and converters only work with matching networks. Petrol cars need refineries and filling stations; gas boilers need a gas grid; blast furnaces need coke ovens and coking coal; airports need jet fuel supply chains. Changing one part means changing the others, and nobody wants to build charging stations before there are electric cars, or buy the cars before there are stations. Each piece of the old system is cheap partly because the rest of it already exists and has been paid for.

Lock-in also covers institutions: grid codes written for large spinning generators, tariff designs, utility business models, skills and supply chains. These can change faster than steel and concrete, and good policy targets them. India's switch to competitive auctions for solar and wind contracts in the late 2010s, which drove bid prices down sharply, is an example of institutional change unlocking physical change.

Data Typical working lives of energy assets

| Asset | Typical life | What it locks in |
|---|---|---|
| Car or two-wheeler | 10 to 20 years | fuel type and refuelling network |
| Industrial boiler or furnace | 20 to 40 years | fuel supply and process design |
| Coal or gas power station | 30 to 60 years | fuel contracts, mines, pipelines |
| Nuclear reactor | 40 to 80 years | fuel cycle and grid role |
| Refinery or pipeline | 40 years and more | oil product demand and trade routes |
| Hydro dam | about a century | river use and storage |
| Building | 50 to 100 years or more | heating and cooling needs, gas connections |

Ranges are indicative; well-maintained assets often outlive their design lives.
 Source: Smil, Energy Transitions: Global and National Perspectives (2017), via Smil Mastery Course, M9 'Why transitions are slow'  Case

#### Why a young coal fleet is a financial question

In its 2024 outlook the IEA expected India to add about 60 GW of coal-fired capacity by 2030. A unit commissioned in 2029 would, on a 40-year life, run until about 2069, close to India's target year of 2070 for net zero. For a lender or an equity investor the key question is not whether solar is cheaper per kWh, which it already is, but how many hours a year these plants will actually run, at what tariff, and who bears the cost if they run far less than planned. That is how stranded assets are created.

- Smil, Energy Transitions: Global and National Perspectives (2017) · via Smil Mastery Course, M9 'Why transitions are slow'
- Smil, Energy Myths and Realities: Bringing Science to the Energy Policy Debate (2010) · via Smil Mastery Course, M9 'Why transitions are slow'
- IEA, World Energy Outlook 2024 (2024), India findings as reported by PTI · Outlook Business, 17 October 2024, https://www.outlookbusiness.com/sustainability/india-set-to-lead-global-energy-demand-growth-coal-will-remain-central-iea

### 2.3 Rising demand absorbs much of the new clean supply

The third brake is growth. A transition is a race between new clean supply and rising total demand. If demand grows faster than clean supply, fossil use still rises.

For most of the past two decades that is what happened. World energy use kept climbing, mainly in Asia, and new wind and solar met only part of the increase. Fossil fuels filled the rest, which is why global CO2 emissions kept setting records even as clean energy investment boomed.

In electricity the race is now tipping. Ember's Global Electricity Review 2026 found that in 2025 world electricity demand rose by about 849 TWh, while low-carbon generation rose by about 887 TWh, more than covering the increase. Fossil generation fell slightly, by 0.2%, the first year without growth since the pandemic year of 2020. Solar alone added 636 TWh, a rise of 30% in a single year, and overtook wind. Renewables reached 33.8% of world electricity, edging past coal at 33.0%.

Two cautions keep this in proportion. First, electricity is only about a fifth of final energy. Heat for industry and buildings and fuel for transport are still mostly fossil, and in those uses the race has barely begun. Second, demand growth itself is uncertain. The IEA's World Energy Outlook 2025 expects energy demand to keep rising to 2050 in all its main scenarios, led by emerging economies, above all India and Southeast Asia, with cooling, industry and transport as the big drivers. Data centres and AI attract the headlines but account for under a tenth of projected growth in global electricity demand, though more in the United States.

The lesson is to watch two numbers together: how fast clean supply grows in absolute terms, and how fast total demand grows. Only when the first is larger does fossil use fall, and that is now happening in power but not yet across the whole energy system.

Data World electricity in 2025: demand against clean supply

| Measure | 2025 value |
|---|---|
| Growth in electricity demand | +849 TWh |
| Growth in low-carbon generation | +887 TWh |
| Change in fossil generation | -38 TWh (-0.2%) |
| Solar generation | 2,778 TWh, up 30% |
| Wind generation | up 8.2% |
| Renewables share of generation | 33.8% |
| Coal share of generation | 33.0%, generation down 0.6% |
| Gas share of generation | 21.8% |
| Wind and solar share | 17.3% |
| Average carbon intensity | 458 g CO2-equivalent per kWh |

 Source: Ember, Global Electricity Review 2026 (April 2026), 2025 data, https://ember-energy.org/latest-insights/global-electricity-review-2026/ and https://ember-energy.org/chapter/2025-in-review/  Common misreading

#### Record renewables do not mean falling emissions

News of record solar installations often sits beside news of record CO2 emissions, and both can be true. The Global Carbon Budget projected fossil CO2 at a record 38.1 Gt in 2025, with oil emissions up about 1% and gas up 1.3%, in a year when fossil power generation was flat. Clean electricity can stop the growth of emissions from power stations. On its own it does nothing for cars, ships, aircraft, steel mills or cement kilns until those uses are electrified or switched to other low-carbon fuels.

- Ember, Global Electricity Review 2026 (April 2026) · 2025 data, https://ember-energy.org/latest-insights/global-electricity-review-2026/ and https://ember-energy.org/chapter/2025-in-review/
- IEA, World Energy Outlook 2025 (2025) · Overview and key findings, https://www.iea.org/reports/world-energy-outlook-2025/overview-and-key-findings
- Global Carbon Project, Global Carbon Budget 2025 (November 2025) · 'Fossil fuel CO2 emissions hit record high in 2025', https://globalcarbonbudget.org/fossil-fuel-co2-emissions-hit-record-high-in-2025/
- Smil, How the World Really Works: A Scientist's Guide to Our Past, Present and Future (2022) · via Smil Mastery Course, M9 'Why transitions are slow'

### See it in the table
[Oil Crude oil](https://www.materialinsights.org/energy/crude_oil/)[Kc Coking coal](https://www.materialinsights.org/energy/coking_coal/)[Cu Copper](https://www.materialinsights.org/commodities/copper/)[Al Aluminium](https://www.materialinsights.org/commodities/aluminum/)[St Steel](https://www.materialinsights.org/commodities/steel/)[Si Silicon](https://www.materialinsights.org/commodities/silicon/)[Cem Cement](https://www.materialinsights.org/commodities/cement/)[Blr Boilers, furnaces and stoves](https://www.materialinsights.org/energy/e_combustion_heat/)[DC Data centres](https://www.materialinsights.org/energy/e_data_centres/)

### Check your understanding

Between 2000 and about 2020 new renewables grew roughly 50-fold. What happened to the fossil share of world primary energy?
 The new sources started from a tiny base, and total demand grew, so the fossil share barely moved; part of the decline came from hydro.

In 2025, according to Ember, why did world fossil-fuel generation stop growing?
 Demand rose about 849 TWh while low-carbon output rose about 887 TWh, so fossil generation fell slightly, by about 0.2%.

Which statement about lock-in is most accurate?
 Each part of the old system is cheap partly because the rest exists; replacing one part means replacing the others too.

[← Part 1: What a transition is and how fast transitions run](https://www.materialinsights.org/learn/energy/energy-transitions-climate/p1/)[Mark read · Part 3: Decarbonisation so far, and the hard parts →](https://www.materialinsights.org/learn/energy/energy-transitions-climate/p3/)

## Other sections

- [Module overview](https://www.materialinsights.org/learn/energy/energy-transitions-climate/index.md)
- [What a transition is and how fast transitions run](https://www.materialinsights.org/learn/energy/energy-transitions-climate/p1/index.md)
- [Decarbonisation so far, and the hard parts](https://www.materialinsights.org/learn/energy/energy-transitions-climate/p3/index.md)
- [Carbon dioxide, climate and the paths ahead](https://www.materialinsights.org/learn/energy/energy-transitions-climate/p4/index.md)
- [Key terms, quiz and sources](https://www.materialinsights.org/learn/energy/energy-transitions-climate/review/index.md)