LOW←TECH MAGAZINE English

Thematic Book Series: How Circular is the Circular Economy?

Mon, 22 Jul 2024 00:00:00 +0000

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The circular economy – the newest magical word in the sustainable development vocabulary – promises economic growth without environmental destruction or waste. However, growth makes a circular economy impossible, even if we recycle all raw materials and all recycling is 100% efficient. No technology can change that because it’s not a technological problem. In addition, many modern products are too complex to recycle.

In this series of articles, LOW←TECH MAGAZINE explores how the circularity of various technologies like bicycles, solar panels, and wind turbines evolves. Placing the recycling of resources in a historical context makes clear that we are not moving toward a circular economy but rather increasingly away from it.

Contents table:

How circular is the circular economy?
Can we make bicycles sustainable again?
Plastic waste in the fuel tank?
Recycling animal and human manure is the key to sustainable farming
How to make wind power sustainable again?
Reinventing the small wind turbine
How to build a low-tech solar panel?
How to escape from the Iron Age?

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Patrons get free access to ebooks, as well as early access to new print books at a reduced price.

Other books in the series:

How to build a low-tech internet?, Kris De Decker, Roel Roscam Abbing, Marie Otsuka, 2023. Ebook edition.
How to downsize a transport network?, Kris De Decker, 2023. Ebook edition.
Heating people not spaces, Kris De Decker, 2024. Ebook edition

The Low-tech Magazine archives are also available as a chronological series consisting of four volumes.

How to Escape From the Iron Age?

Mon, 18 Mar 2024 00:00:00 +0000

Image: Steel rebar construction for the concrete foundation of a wind turbine in Gilliam County, US. Image by Goose Chap, Wikimedia Commons (CC BY-SA 4.0)

Trapped in the Iron Age

In 1836, Danish antiquarian and curator Christian Jürgensen Thomsen distinguished three prehistorical eras based on the dominant materials used for weapons and cutting implements: the Stone Age, the Bronze Age, and the Iron Age.¹ Thomsen’s classification refers to the past, but according to his criteria, we have never evolved beyond the Iron Age. Even in the 21st century, iron remains the dominant material, not just for weapons and cutting implements but for about every modern technology.

We now use most iron in the form of steel. However, according to Thomsen’s criteria, we cannot speak of a “Steel Age.” First, steel is merely an alloy of iron (>98%) and carbon (<2%). Second, humans have been producing steel since the beginning of the Iron Age. That is a little-known fact in the Western world, where steel production only took off in the nineteenth century with fossil fuels. However, Asian and African metallurgists developed high-quality steels much earlier, and this knowledge eventually allowed Europeans to do the same – on a much larger scale.²

By 2021, the global iron and steel output reached 1,950 million tonnes (Mt). That is 22 times larger than the combined aluminum and copper output (88 Mt). The global iron and steel output corresponds to five times the global plastics output (391 Mt) and dwarfs the worldwide production of silicon (8.5 Mt) and lithium (0.1 Mt).³⁴ Steel is the fundamental material of industrial societies. Without plastics, lithium, or silicon, we would still be in an industrial society. Without iron and steel, we would be thrown back 3,000 years into the Bronze Age.

Where is all that steel?

The massive presence of steel in industrial society is not so obvious.⁵ At home, we find several steel appliances such as the refrigerator, washing machine, water boiler, bathtub, and cooking, heating, and cooling appliances. However, only 2-3% of total steel production ends up in domestic appliances.⁶⁷⁸ Outdoors, there’s a lot of steel in the form of vehicles. These are especially passenger cars that use around 10% of all steel globally (20% in rich countries). Busses, trucks, trains, and ships add another 4-5%. Altogether that is still less than 20% of the global steel output.

Most steel is embedded in other materials, located underground, or far away from residential areas.

Most steel is embedded in other materials, located underground, or far away from residential areas. More than half of global steel production goes into construction, which includes buildings (residential, commercial, industrial) and infrastructures (bridges, tunnels, harbors, canals, runways, oil rigs, refineries, pipelines, power plants, transmission lines, railways, subways, and so on). Much of that steel is embedded in concrete. Reinforced concrete is the world’s primary building material, and concrete is the only material that can match the output of steel (1,819 Mt in 2021).

Roughly 15% of global steel production serves to make machinery, including machine tools, industrial equipment, electrical hardware, and construction, mining, and farming machines. Even products made of other materials – such as other metals, plastics, and wood – are shaped by steel tools.⁵ The final 15% of steel production ends up in a variety of objects, from screws over food packaging to furniture and shipping containers.⁶⁷⁸

Image: Reinforced concrete is the world’s primary building material. Hole on Interstate 84, US. Image by Tony George, Oregon Department of Transportation, Wikimedia Commons (CC BY 2.0).

The environmental footprint of the steel industry

Steel is often presented as one of the most sustainable materials. Unlike plastics, steel can be recycled without any loss in quality. The steel industry has made great advances in energy efficiency, more so than many other industries. Making one ton of crude steel now requires roughly 20 gigajoules (GJ) of primary energy on average – three times less than in 1950.⁹ This compares very favorably to other materials such as aluminum (175 GJ/t), plastics (80-120 GJ/t), or copper (45 GJ/t).⁷ Unlike plastics, steel is a biodegradable material.¹⁰ Finally, iron ore is not in short supply. It makes up 5 percent of the Earth’s crust and is fourth in abundance among the elements.¹¹ For comparison, copper only makes up 0.01%.⁵

However, despite all these advantages, the global iron and steel industry consumes more energy and produces more carbon emissions than any other industry. The total primary energy use of crude steel production was 39 exajoules (EJ) in 2021, which corresponds to 7% of all energy used worldwide in that year (595 EJ). The greenhouse gas emissions are even higher because around 75% of energy use comes from coal – the fuel with the highest carbon emissions. In 2021, the iron and steel industry produced 3.3 Gt of carbon emissions, roughly 9% of global emissions (36.3 Gt).¹² The concrete industry follows closely with 8%.

The iron and steel industry consumes more energy and produces more carbon emissions than any other industry.

The estimates above come from the World Steel Association and the International Energy Agency. These data are available for all metals and have been documented over a long period, allowing for historical comparisons. However, they only refer to the smelting of the metal. They do not include the energy use and carbon emissions for mining and transporting iron ore, coal, limestone, scrap, and steel products. Nor do they include the energy and emissions for coke production and ore preparation – all essential to the steel production process.⁷

Scientific studies that have set wider boundaries for the iron and steel industry conclude that the energy cost of steel production increases by 50% to 100%.¹³ One report concludes that the methane emissions from metallurgical coal mining alone could increase emissions by 27%. Another study estimates that seaborne transport of iron ore and steel adds 10-15% extra emissions.¹⁴¹⁵ Iron and steel production also create other environmental problems, such as high water use, solid waste production, and significant air and water pollution.

The carbon footprint of the iron and steel industry is incompatible with current ambitions to eliminate net carbon emissions by 2050, even less so because steel production is very likely to expand further. Steel production grew tenfold since 1950 and doubled between 2000 and 2020, growing faster than many researchers had predicted.¹⁶ Furthermore, efficiency gains have decreased, and there is a scientific consensus that current technologies have reached their thermodynamic limits.⁷⁹¹⁷ During the last two decades, the average energy use for the production of 1 ton of steel has remained around 20 GJ/t.⁹¹⁸

How to make steel without fossil fuels?

There are two ways to make steel, and one is much more sustainable than the other.¹⁹ On the one hand, there is the blast furnace or basic oxygen furnace, in which steel is made from iron ore and coal. This technology is – in its essential form – 2000 years old. On the other hand, there is the electric arc furnace, in which steel is made from steel scrap and electricity. The electric arc furnace, which is a relatively new technology, consumes much less energy than the blast furnace, makes use of a recycled resource (no need to mine iron ore), and works without the direct use of coal or other fossil fuels (the electricity can be supplied by solar, wind, or atomic power).

The most energy-efficient electric arc furnaces now consume less than 300 kilowatt-hours of electricity per ton of steel produced.⁹²⁰ Hypothetically, if we had produced all steel in 2021 (1,950 Mt) in such furnaces, the total power consumption of the global iron and steel industry would have been only 585 terawatt-hours (Twh). That corresponds to just one-third of all electricity generated by wind turbines worldwide in the same year (1,848 Twh). Unfortunately, more than 70% of global steel output was made in blast furnaces fed by coal and iron ore.⁹²⁰ A blast furnace consumes twenty times more energy and cannot be operated by electricity because coal is both the fuel source and the chemical reductant. The combustion of coal produces carbon monoxide that reduces the iron from its ore.⁷

Not enough scrap available

The solution seems obvious: let’s produce all that steel in electric arc furnaces. However, this is impossible. There’s not enough scrap available: the continuous growth of the global steel output makes a circular flow of resources impossible.²¹ It takes decades before most steel becomes available for recycling. For example, there is 543 Mt of steel stocked in ships.²² The scrap available for recycling in 2021 corresponds to the production level of 1965 when global steel production was less than one-quarter of what it is today (450 Mt).⁹¹⁰¹⁵²³ Consequently, the other three quarters need to be produced in blast furnaces using coal and freshly mined iron ore.

Image: Cars for scrapping at the Port of Cardiff. Gareth James via Wikimedia Commons (CC BY-SA 2.0).

Nowadays, China produces roughly half of the steel in the world and does that almost exclusively (+90%) in blast furnaces using coal and iron ore. Many other steelmaking nations have a higher share of electric arc furnaces. However, it makes little sense to point the finger at China. First, the US and Europe have outsourced many of their industries to China since the 2000s, a trend that corresponds neatly with the growing steel output in that country. Furthermore, twenty to forty years ago, China hardly used any steel. Consequently, there is almost no scrap available. China has no other choice than to use blast furnaces.²⁴

Ever higher grades of steel

A second obstacle is the continuous development of higher grades of steel. There are now over 2,500 different types of steel with a variety of properties, such as increased strength, tolerance to high temperatures, or corrosion resistance.⁷⁹²³²⁵ Although these higher quality steels can be produced in electric arc furnaces, they are not made from scrap, and they have much higher energy use.

Steel available for recycling forms a mix of steel grades. That mix is suitable for making plain carbon steel but not highly alloyed steels, which require scrap with similar qualities. However, that scrap is not available. For example, stainless steel, the most produced special steel grade, has a recycling rate of only 15%. Almost 60 Mt of stainless steel was produced in 2021, compared to only 4 Mt in 1980.²⁶ The traditional use of stainless steel was in cutlery, surgical tools, and medical and food processing equipment. However, it is now also used in the construction of tunnels and outdoor furniture, wastewater treatment, seawater desalination, nuclear engineering, and the production of biofuels.⁷

The low recycling rate and the need for the extraction of additional elements such as chrome and nickel make higher grades of steel more energy-intensive to produce. For example, stainless steel production requires almost 80 GJ per ton, four times more than the production of plain carbon steel.⁷²³ The continuous development of higher-grade steels is stimulated by environmental legislation (such as the use of lighter steel in cars) and by competition from other materials, mainly aluminum and plastic composites.⁷⁹²³²⁵ Ironically, the competition with these materials, which consume even more energy, makes steel less and less sustainable.

Steel and renewable energy

The steel industry is heavily dependent on the energy supply, but the energy supply is also heavily dependent on the steel industry. Almost 10% of the global steel output goes into building and maintaining energy supply infrastructure. That amount corresponds to the entire steel output in 1950. A great share of that steel goes to gas and oil infrastructure.²⁷. Oil and gas mining, production, and transportation require steel for offshore drilling platforms, pipelines, refineries, tankers, and storage tanks. Coal mining depends on steel for cutters, loaders, conveyors, excavators, and trucks.⁷

Unfortunately, the planned switch to low-carbon energy sources and the electrification of heating and transport technologies will not decrease our dependency on the steel industry – on the contrary. A low-carbon power grid requires much more steel (and other materials) than an infrastructure based on fossil fuels. Wind and solar power are very diffuse power sources compared to fossil fuels. Therefore, it takes much more materials (and land) to produce the same energy. In jargon, wind and solar have low “power density” or high “material intensity.”²⁸²⁹³⁰³¹³²

A low-carbon power grid requires much more steel than an infrastructure based on fossil fuels.

The “steel intensity” of thermal gas and coal power plants is between 50 and 60 tonnes of steel per megawatt of installed power.³³ Hydroelectric power plants have a lower steel intensity, with 20-30 tonnes of steel per MW.⁷³³ Atomic power’s steel intensity is also lower at between 20 and 40 tonnes of steel per installed MW.³³³⁴ On the other hand, solar PV requires between 40 and 170 tonnes of steel per installed MW.³³³⁵ Although there is little or no steel in the solar panels themselves, it’s the material of choice for the structures that support them.

Steel and wind power

The most steel-intensive power source – by far – is the modern wind turbine. The steel intensity of a wind turbine depends on its size. A single, large wind turbine requires significantly more steel per megawatt of installed power than two smaller wind turbines.³⁶ For example, a 3.6 MW wind turbine with a 100-meter tall tower requires 335 tons of steel (83 tons/MW), while a 5 MW wind turbine with a 150-meter tall tower needs 875 tons of steel (175 tons/MW).³⁷ The trend is towards taller wind turbines and a higher steel intensity.

Image: Steel towers for wind turbines in the port of Rotterdam. Image: Melle Smets.

Steel consumption further increases for offshore wind turbines. Onshore wind power plants rely on reinforced concrete for their foundations, but offshore wind turbines need massive steel structures such as monopiles and jackets.³⁸ The steel intensity for offshore wind turbines is calculated to be around 450 tonnes per MW for a 5 MW turbine – eight times higher than the steel intensity of a thermal power plant.³⁶. As these wind turbines get taller and move into deeper waters, their steel use further increases.

The most popular offshore wind turbine nowadays has a capacity of 7 MW, while the largest ones have a capacity of 14 MW.³⁶ If we make a conservative estimate based on the data above (the steel intensity doubles for every doubling of the power capacity), a 14 MW offshore wind turbine would require 1,300 tons of steel per MW or 18,200 tonnes in total. Such a wind turbine thus consumes 24 times more steel than a coal or gas power plant of the same power capacity.

Shorter life expectancy

The difference between renewable power sources and fossil fuels becomes even larger if the steel intensity is calculated per unit of energy rather than power (MWh instead of MW). In contrast to coal and gas power plants, the output of wind and solar power plants depends on the weather, and they do not always produce their maximum power capacity. Therefore, replacing 1 MW of fossil electricity generation capacity requires the installation of (on average) 4 MW of solar power or 2 MW of wind power.³⁹ A 14 MW offshore wind turbine thus has a steel intensity that is almost 50 times higher than a fossil fuel power plant for every kilowatt-hour of electricity produced.⁴⁰

A 14 MW offshore wind turbine has a steel intensity that is almost 50 times higher than a fossil fuel power plant for every kilowatt-hour of electricity produced.

Solar and wind power plants also have shorter lifetimes (20-30 years) compared to thermal power plants (30-60 years).³¹ While this does not affect the steel intensity per MW of power installed, it again increases the steel intensity per unit of energy produced over time. That does not always lead to a doubling of steel use because foundations for offshore wind turbines and structures for solar panels may have longer lifetimes than the power sources they support and could thus be reused.⁴¹

Power transmission infrastructure

The data above only include the steel used in the power plants themselves. For fossil fuel power plants, they do not include the steel used in the pipelines, oil rigs, coal excavators, and the like. However, the same goes for the low-carbon power sources. Because they need much more resources than thermal power plants (steel but also other metals and materials), they depend on a global mining and transport infrastructure that is just as steel-intensive as the supply chain for fossil fuels.

Furthermore, because they are more diffuse power sources with intermittent and unpredictable power production, often located far away from energy consumption centers, renewable power plants drive the expansion of transmission infrastructure. That infrastructure is also based on steel – from switchyard equipment over towers to conduction cables.²⁸²⁹³⁰³¹³²⁴²

Finally, low-carbon power sources also have a high need for special grades of steel, which are more energy-intensive to produce. Steel for off-shore wind turbines should resist corrosion, and stainless steel is increasingly used for solar panel support structures.⁴³ Electrical lamination steel (iron-silicon) is indispensable for transformers in the power network.⁷ Nuclear power plants may have a relatively low steel intensity but are completely built up of energy-intensive specialty steels. For example, cladding the fuel elements containing fissionable uranium requires zirconium steel, while all structural elements contain austenitic stainless steel.⁷⁴⁴

Low carbon grid cannot be made from recycled steel

The high steel intensity of low carbon power sources confronts us with a so-called “catch-22”, a situation in which there seems to be no escape from a problem no matter what we do. We need much more steel if we replace thermal power plants with renewable ones. Because there is not enough steel scrap available, we can only produce that extra steel from iron ore in blast furnaces burning fossil fuels. To address climate change, we need to build low-carbon sources quickly and in great numbers. However, to achieve circular material flows and build low-carbon power sources from scrap and renewable electricity, we would have to do the opposite: slow down the development of a low-carbon power grid.

Image: Steel foundations for off-shore wind turbines. Image by Glen Wallace, Wikimedia Commons (CC BY 2.0).

A well-cited study from 2013 concluded that if wind and solar power would supply 25,000 Twh of electricity – which corresponds to total global electricity demand in 2021 – we need about 3,200 Mt of steel to build the power plants alone.³³⁴⁵ Global electricity demand is projected to grow to between 52,000 and 71,000 terawatt-hours in 2050, which would increase the extra steel demand to between 6,400 and 8,960 Mt.⁴⁶ Spread out over the lifetime of solar panels and wind turbines (25 years), we would have to produce 256 to 358 Mt extra steel per year to make wind turbines and solar panel structures – comparable to the steel demand for passenger cars (195 Mt) and other transportation modes (98 Mt) combined.

That is still a very optimistic estimation. Electricity demand only makes up around 20% of total energy demand. If the total energy demand (177,000 Twh in 2021) would be supplied by wind and solar, we would need 22,400 Mt of steel. That’s an extra 896 Mt steel per year – as much as the global production in the early 2000s. You could argue that electricity can be used more efficiently than fossil fuels, for example, in cars and heating systems. However, at the same time, total energy demand is expected to rise further, countering the gains made by increased energy efficiency.

The high-tech solutions

The steel industry counts on technological solutions to make steel production carbon neutral. One option is to replace coal by gas, an approach that is already common in the Middle East and North America. Gas-based steelmaking results in somewhat lower carbon emissions, but they are still much higher than in the case of the electric arc furnace. Therefore, most attention goes to hydrogen, which can replace purified coal (coke) as a reducing agent in a direct reduction shaft furnace.⁴⁷ However, hydrogen-based steelmaking does not offer an escape from the catch-22 because it further increases the need for a steel-intensive infrastructure.

The production of hydrogen is energy-intensive. It takes 50-55 kilowatt-hour to make 1 kg of hydrogen and 60 kg of hydrogen to make 1 ton of steel.⁴⁷ The production of 1 ton of steel from hydrogen thus consumes 3,000 kWh of electricity, which is ten times higher than the electricity use of an electric arc furnace making steel from scrap. Consequently, hydrogen-based steelmaking requires roughly ten times more wind turbines and solar panels than scrap-based steel production – and thus ten times more steel. On top of this comes the steel for building the pipelines and storage tanks that are part of the hydrogen infrastructure.

Image: Worker in a blast furnace. Bundesarchiv, B 145 Bild-F079044-0020 / CC-BY-SA 3.0.

Carbon capture and storage, in which the carbon emissions of steelmaking plants are captured and then stored underground, faces the same problems. It requires a steel infrastructure and extra energy, thus indirectly raising the use of fossil fuels. Reverting to older, preindustrial steelmaking processes is not the answer either. Today’s blast furnace is essentially still the blast furnace from earlier centuries, only much more energy efficient.⁷

The low-tech solutions

The picture painted above seems to offer little hope for carbon-neutral steelmaking and power production. However, there is a low-tech solution that could achieve it. We could adjust steel production to the available scrap supply both in quantity and quality. That would allow us to produce all steel from scrap in electric arc furnaces, dramatically reducing energy consumption and eliminating almost all carbon emissions. Of course, the intent should not be to replace steel with plastic composites and aluminum because they are even more energy-intensive to produce. The only solution is to reduce material use overall.

We could adjust steel production to the available scrap supply both in quantity and quality.

Reducing the steel output and using more common steel grades would not bring us back to the Bronze Age. As noted, global end-of-life ferrous scrap availability was approximately 450 Mt in 2021, which would allow us to produce roughly one-quarter of the current steel output. Furthermore, the scrap supply will continue to rise for the next 40 years, enabling us to produce more and more low-emission steel each year. By 2050, scrap availability is expected to rise to about 900 Mt, almost half of today’s global steel production.⁴⁸ All that extra steel could be invested in expanding the low-carbon power grid without raising emissions first.

There is a lot of room to reduce the steel intensity of modern society. All our basic needs – and more – could be supplied with much less steel involved. For example, we could make cars lighter by making them smaller. That would bring energy savings without the need for energy-intensive high-grade steel. We could replace cars with bicycles and public transportation so that more people share less steel. Such changes would also reduce the need for steel in the road network, the energy infrastructure, and the manufacturing industry. We would need fewer machine tools, shipping containers, and reinforced concrete buildings. Whenever steel intensity is reduced, the advantages cascade throughout the whole system. Preventing corrosion and producing steel more locally from local resources would also reduce energy use and emissions.¹⁰¹⁴

The continuous growth of the steel output – the increasing steel intensity of human society – makes sustainable steel production impossible. No technology can change that because it’s not a technological problem. Like forestry can only be sustainable if the wood demand does not exceed the wood supply, steel is sustainable or not depending on the balance between (scrap) supply and (steel) demand. We may not be able to escape the Iron Age, but we have an option to escape the catch-22 that inextricably links steel production with fossil fuels.⁴⁹

Thomsen, Christian Jürgensen. “Cursory View of the Monuments and Antiquities of the North.” Guide to Northern Archaeology by the Royal Society of Northern Antiquaries of Copenhagen (1848): 25-104. See also: Eskildsen, Kasper Risbjerg. “Christian Jürgensen Thomsen (1788–1865): Comparing Prehistoric Antiquities.” History of Humanities 4.2 (2019): 263-267. And: Briggs, C. Stephen. “From Genesis to Prehistory: the archaeological Three Age System and its contested reception in Denmark, Britain, and Ireland. By Peter Rowley-Conwy. 226mm. Pp xix+ 362, 55 b&w ills. Oxford: Oxford University Press, 2007. ISBN 9780199227747.£ 65 (hbk).” The Antiquaries Journal 88 (2008): 474-478. ↩︎
Forthcoming article, Kris De Decker, Low-tech Magazine. Subscribe to Low-tech Magazine’s newsletter. ↩︎
Idoine, N. E., et al. “World mineral production 2017-21.” (2023). https://nora.nerc.ac.uk/id/eprint/534316/1/WMP_2017_2021_FINAL.pdf ↩︎
Katz-Lavigne, Sarah, Saumya Pandey, and Bert Suykens. “Mapping global sand: extraction, research and policy options.” (2022). https://repository.uantwerpen.be/docman/irua/1428b3/183490cc.pdf ↩︎
Colás, Rafael, and George E. Totten, eds. Encyclopedia of iron, steel, and their alloys (Online version). CRC Press, 2016. ↩︎ ↩︎ ↩︎
https://www.steelonthenet.com/consumption.html. Meanwhile the data on this page have been updated for 2023. ↩︎ ↩︎
Smil, Vaclav. Still the iron age: iron and steel in the modern world. Butterworth-Heinemann, 2016. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
“Steel in buildings and infrastructure”, World steel association. https://worldsteel.org/steel-topics/steel-markets/buildings-and-infrastructure/ ↩︎ ↩︎
Conejo, Alberto N., Jean-Pierre Birat, and Abhishek Dutta. “A review of the current environmental challenges of the steel industry and its value chain.” Journal of environmental management 259 (2020): 109782. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Between 25 and 33% of the annual steel production is destroyed once in service by corrosion. See: Iannuzzi, M., and G. S. Frankel. “The carbon footprint of steel corrosion.” npj Materials Degradation 6.1 (2022): 101. https://www.nature.com/articles/s41529-022-00318-1.pdf ↩︎ ↩︎ ↩︎
“Iron”, Encyclopedia Britannica ↩︎
The potential of hydrogen for decarbonising steel production. European Parliament: https://www.europarl.europa.eu/RegData/etudes/BRIE/2020/641552/EPRS_BRI(2020)641552_EN.pdf ↩︎
Lenzen, Manfred, and Christopher Dey. “Truncation error in embodied energy analyses of basic iron and steel products.” Energy 25.6 (2000): 577-585. & Oda, Junichiro, et al. “International comparisons of energy efficiency in power, steel, and cement industries.” Energy Policy 44 (2012): 118-129. Both found in: Smil, Vaclav. Still the iron age: iron and steel in the modern world. Butterworth-Heinemann, 2016. ↩︎
“Pedal to the metal”, Caitlin Swalec, Global Energy Monitor, June 2022. https://globalenergymonitor.org/wp-content/uploads/2022/06/GEM_SteelPlants2022.pdf ↩︎ ↩︎
Yellishetty, Mohan, P. G. Ranjith, and A. Tharumarajah. “Iron ore and steel production trends and material flows in the world: Is this really sustainable?.” Resources, conservation and recycling 54.12 (2010): 1084-1094. ↩︎ ↩︎
See, for example: Hatayama, Hiroki, et al. “Outlook of the world steel cycle based on the stock and flow dynamics.” Environmental science & technology 44.16 (2010): 6457-6463. This paper predicted steel demand to reach 1.8 billion tonnes only by around 2025. ↩︎
De Beer, Jeroen. Potential for industrial energy-efficiency improvement in the long term. Vol. 5. Springer Science & Business Media, 2013. ↩︎
Wang, R. Q., et al. “Energy saving technologies and mass-thermal network optimization for decarbonized iron and steel industry: A review.” Journal of Cleaner Production 274 (2020): 122997. ↩︎
About 5% of global steel is produced by a third method: gas-based direct iron reduction. These furnaces use gas instead of coal and have therefore lower carbon emissions. However, emissions are still much higher than in the case of the electric arc furnace. Gas-based steelmaking mainly happens in the Middle East and North America. ↩︎
He, Kun, and Li Wang. “A review of energy use and energy-efficient technologies for the iron and steel industry.” Renewable and Sustainable Energy Reviews 70 (2017): 1022-1039. This source gives a value of 1-1.5 GJ/ton of crude steel. ↩︎ ↩︎
This also holds true for many other materials. See: “How circular is the circular economy?”, Kris De Decker, Low-tech Magazine, November 2018. https://qelnixcor.cloud/2018/11/how-circular-is-the-circular-economy/ ↩︎
Kong, Xianghui, et al. “Steel stocks and flows of global merchant fleets as material base of international trade from 1980 to 2050.” Global Environmental Change 73 (2022): 102493. ↩︎
ODPADKA, PROIZVODNJA JEKLA IZ JEKLENEGA. “Scrap-based steel production and recycling of steel.” Materiali in tehnologije 34.6 (2000): 387. ↩︎ ↩︎ ↩︎ ↩︎
In the West, the expansion of steel use happened over a period of 150 years, in tandem with technological evolution. In contrast, China compressed this technological evolution in just a few decades: shipping and railways, electrification, steel buildings, the car and the airplane, the internet, and renewable power technologies. There are still large parts of the world where the steel intensity of society is very low, such as India and Africa. There is thus still a lot of room for the growth of the steel output. Source: Smil, Vaclav. Still the iron age: iron and steel in the modern world. Butterworth-Heinemann, 2016. ↩︎
AHHS Application Guidelines, WorldAutoSteel. ahssinsights.org/news/intro ↩︎ ↩︎
Sverdrup, Harald Ulrik, and Anna Hulda Olafsdottir. “Assessing the long-term global sustainability of the production and supply for stainless steel.” BioPhysical Economics and Resource Quality 4 (2019): 1-29. ↩︎
Conseil, Laplace. “Impacts of energy market developments on the steel industry.” 74th Session of the OECD Steel Committee, Paris, France (2013). Found in: Smil, Vaclav. Still the iron age: iron and steel in the modern world. Butterworth-Heinemann, 2016. ↩︎
Deetman, Sebastiaan, et al. “Projected material requirements for the global electricity infrastructure–generation, transmission and storage.” Resources, Conservation and Recycling 164 (2021): 105200. ↩︎ ↩︎
How (Not) to Run a Modern Society on Solar and Wind Power Alone, Kris De Decker, Low-tech Magazine, September 2017. https://qelnixcor.cloud/2017/09/how-not-to-run-a-modern-society-on-solar-and-wind-power-alone/ ↩︎ ↩︎
Kleijn, René, et al. “Metal requirements of low-carbon power generation.” Energy 36.9 (2011): 5640-5648. ↩︎ ↩︎
Weißbach, Daniel, et al. “Energy intensities, EROIs (energy returned on invested), and energy payback times of electricity generating power plants.” Energy 52 (2013): 210-221. ↩︎ ↩︎ ↩︎
Chen, Zhenyang, Rene Kleijn, and Hai Xiang Lin. “Metal requirements for building electrical grid systems of global wind power and utility-scale solar photovoltaic until 2050.” Environmental Science & Technology 57.2 (2022): 1080-1091. ↩︎ ↩︎
Vidal, Olivier, Bruno Goffé, and Nicholas Arndt. “Metals for a low-carbon society.” Nature Geoscience 6.11 (2013): 894-896. The data are in the supplementary info: https://www.nature.com/articles/ngeo1993#Sec5 ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
“Energy”, American Iron and Steel Institute. https://www.steel.org/steel-markets/energy/ ↩︎
“Steel is the power behind renewable energy”, Arcelor Mittal. https://constructalia.arcelormittal.com/en/news_center/articles/steel-is-the-power-behind-renewable-energy#:~:text=Steel%3A%20a%20key%20material%20in%20a%20less%20carbon%2Dintensive%20world&text=Without%20steel%2C%20none%20of%20the,Schrijver%2C%20CEO%20of%20ArcelorMittal%20Projects. ↩︎
Topham, Eva, et al. “Recycling offshore wind farms at decommissioning stage.” Energy policy 129 (2019): 698-709. ↩︎ ↩︎ ↩︎
Gervásio, Helena, et al. “Comparative life cycle assessment of tubular wind towers and foundations–Part 2: Life cycle analysis.” Engineering structures 74 (2014): 292-299. & Rebelo, Carlos, et al. “Comparative life cycle assessment of tubular wind towers and foundations–Part 1: Structural design.” Engineering structures 74 (2014): 283-291. ↩︎
Assessing the significance of steel to the global wind industry, S&P Global, Commodity Insights. December 2021. https://www.spglobal.com/commodityinsights/en/ci/research-analysis/assessing-the-significance-of-steel-to-the-global-wind-industry.html ↩︎
Bolson, Natanael, Pedro Prieto, and Tadeusz Patzek. “Capacity factors for electrical power generation from renewable and nonrenewable sources.” Proceedings of the National Academy of Sciences 119.52 (2022): e2205429119. https://www.pnas.org/doi/10.1073/pnas.2205429119 ↩︎
This result corresponds well with Vidal, Olivier, Bruno Goffé, and Nicholas Arndt. “Metals for a low-carbon society.” Nature Geoscience 6.11 (2013): 894-896. The data are in the supplementary info: https://www.nature.com/articles/ngeo1993#Sec5 ↩︎
For off-shore wind turbines, the lifetime of the foundations is estimated to be 100 years, so in principle they could serve for replacement wind turbines of the same size. On the other hand, it is not self-evident that these steel foundations will eventually be recycled. First, only around 10% of decommissioning costs can be recovered by recycling the metal, meaning that it is not economically and perhaps even energetically interesting to do it. Second, in some cass marine life has flourished around the foundations. The four offshore wind farms that had been decomissioned in 2019 lasted for 15, 18, 20 and 26 years. Source: Topham, Eva, et al. “Recycling offshore wind farms at decommissioning stage.” Energy policy 129 (2019): 698-709. ↩︎
See https://www.fedsteel.com/insights/steels-role-in-the-us-power-infrastructure/ ↩︎
See https://industry.arcelormittal.com/products-solutions/Products_in_the_spotlight/magnelis ↩︎
Maziasz, Philip J., and Jeremy T. Busby. Properties of austenitic stainless steels for nuclear reactor applications. Oak Ridge National Lab.(ORNL), Oak Ridge, TN (United States), 2012. ↩︎
Part of this has already been built. The researchers start from the solar and wind power production in 2013, which was 400 Twh, while both power sources produced 2,894 Twh in 2021. ↩︎
Electricity consumption worldwide from 2000 to 2022, with a forecast for 2030 and 2050, by scenario. Statista. https://www.statista.com/statistics/1426308/electricity-consumption-worldwide-forecast-by-scenario/#:~:text=According%20to%20a%20recent%20forecast,on%20the%20energy%20transition%20scenario ↩︎
Bhaskar, Abhinav, et al. “Decarbonizing primary steel production: Techno-economic assessment of a hydrogen based green steel production plant in Norway.” Journal of Cleaner Production 350 (2022): 131339. ↩︎ ↩︎
Scrap use in the steel industry, World Steel Association. May 2021. https://worldsteel.org/wp-content/uploads/Fact-sheet-on-scrap_2021.pdf ↩︎
Another motivation for reducing the steel intensity of modern society is to limit the consequences of geopolitical conflicts. The more steel we produce for peaceful purposes, the more steel becomes available for war and destruction. Remarkably, the production of military equipment is absent from modern steel statistics, and if mentioned, its share is very low. However, in times of war, steelmaking facilities switch to producing steel for military purposes. The steel industry can thus be converted into a weapons industry at any moment, and there is now a lot more steel production capacity available than there has ever been in history. ↩︎

Can We Make Bicycles Sustainable Again?

Tue, 28 Feb 2023 00:00:00 +0000

Illustration: [Diego Marmolejo](https://www.instagram.com/ddidak/).

Cycling is sustainable, but how sustainable is the bicycle?

Cycling is one of the most sustainable modes of transportation. Increased ridership reduces fossil fuel consumption and pollution, saves space, and improves public health and safety. However, the bicycle itself has managed to elude environmental critique. ¹² Studies that calculate the environmental impact of cycling almost always compare it to driving, with predictable results: the bicycle is more sustainable than the car. Such research may encourage people to cycle more often but doesn’t encourage manufacturers to make their bicycles as sustainable as possible.

For this article, I have consulted academic studies that compare different types of bicycles against each other or focus on the manufacturing stage of a particular two-wheeler. That kind of research was virtually non-existent until three or four years ago. Using the available material, I compare different generations of bicycles. Set in a historical context, it becomes clear that the resource use of a bike’s production increases while its lifetime is becoming shorter. The result is a growing environmental footprint. That trend has a clear beginning. The bicycle evolved very slowly until the early 1980s and then suddenly underwent a fast succession of changes that continues up to this day.

There are no studies about bicycles built before the 1980s. Life cycle analyses, which investigate the resource use of a product from “cradle” to “grave,” only appeared in the 1990s. However, the benchmark for a sustainable bicycle stands in the room where I write this. It’s my 1980 Gazelle Champion road bike – now 43 years old. I bought it ten years ago in Barcelona from a tall German guy who was leaving the city. He had tears in his eyes when I walked away with it. I have a second road bike, a Mercier from 1978. That is my spare vehicle in case the other one breaks and I don’t have the time for immediate repairs. I have two more road bikes parked in Belgium, where I grew up and where I still travel a few times a year (by train, not by bike). These are a Plume Vainqueur from the late 1960s and a Ventura from the 1970s.

The main reason why I have opted for old bicycles is that they are much better than new bicycles. Most people don’t realize that, so they are also much cheaper. My four bikes cost me just 500 euros in total. That would buy me only one low-cost new road bike, and such a vehicle surely won’t last 40 to 50 years – as we shall see. Of course, it’s not just old road bikes which are better. The same goes for other types of bicycles built before the 1980s. I ride road bicycles because I cover relatively long distances, usually between 35 and 50 km round trip.

Image: The bicycle I use most often, a Gazelle Champion from 1980. It has covered at least 30,000 km since I bought it in 2013.

What bicycles are made of

The first significant change in the bicycle manufacturing industry was the switch from steel to aluminium bicycles. Before the 1980s, virtually all bikes were made from steel. They had a steel frame, wheels, components and parts. Nowadays, most bicycle frames and wheels are built from aluminum. The same goes for many other bike parts. More recently, an increasing number of cycles have frames and wheels made from carbon fibre composites. Some bike frames are built from titanium or stainless steel. All of these materials are more energy intensive to produce than steel. Furthermore, while steel and aluminum can be recycled and repaired, composite fibres can only be downcycled and have poor repairability. ³

Several studies have compared the energy and carbon costs of bicycle frames and other components made from these different materials – which all have different strength-to-weight ratios. That research has some limitations. Scientists use crude methods because they lack detailed energy data from bike manufacturing processes, and some studies come from manufacturers who pay researchers to review the sustainability of their products. Nevertheless, all put together, the results are pretty consistent. For the sake of brevity, I focus on emissions (CO2 = CO2-equivalents) and ignore other environmental impacts.

Before the 1980s, virtually all bicycles were made from steel.

Reynolds, a British manufacturer known for its bicycle tubing, found that making a steel frame costs 17.5 kg CO2, while a titanium or stainless steel frame costs around 55 kg CO2 per frame – three times as much. ⁴ Starling Cycles, a rare producer of steel mountain bikes, concluded that a typical carbon frame uses 16 times more energy than a steel frame. ⁵ (That would be 280 kg CO2). An independent 2014 study – the first of its kind – calculated the footprint of an aluminum road bike frame with carbon fork from the “Specialized” brand and found the cost to be 2,380 kilowatt-hours of primary energy and over 250 kg of carbon – roughly 14 times that of a steel frame (without fork) as calculated by Reynolds. ²

A bicycle is more than a frame alone. Life cycle analyses of entire bikes show that the carbon footprint of all the other components is at least as large as that of a steel frame. ⁶ Scientists have calculated the lifetime carbon emissions of a steel bike at 35 kg CO2, compared to 212 kg CO2 for an aluminum bicycle. ⁷⁸ The most detailed life cycle analysis sets the carbon footprint for an 18.4 kg aluminum bicycle at 200 kg CO2, including its spare parts, for a lifetime of 15,000 km. The main impact phase is the preparation of materials (74%; aluminum, stainless steel, rubber), followed by the maintenance phase (15.5% for 3.5 new sets of tires, six brake pads, one chain, and one cassette) and the assembly phase (5%). ⁹

Where & how bicycles are made

My steel bicycles date from a time when most industrialized countries had long-established domestic bicycle industries serving their national market. ³ These industries collapsed in Europe and North America following neoliberal globalization in the late 1970s. China opened to foreign investment and quickly became the largest bicycle manufacturer in the world. During the last two decades, China has made two-thirds of the world’s bicycles (60-70 million of 110 million annually). Most of the rest come from other Asian countries. Europe is back to producing ten million bikes annually, but the US only manufactures 60,000 bicycles per year. ³

Throughout the twentieth century, manufacturing bicycles required substantial inputs of human labor. ³ According to the Routledge Companion to Cycling, “wheels were spoked and trued manually; frames were built by hand; saddle making was laborious; headsets, gear clusters (blocks), brake cables and gears were physically bolted on.” Since the 2000s, automation has considerably reduced the need for human labor. The largest Chinese bike manufacturer, which builds one-fifth of the world’s bicycles, has 42 bicycle assembly lines making 55,000 bicycles a day – almost as much as the US in a year. ³

Domestic bicycles industries in Europe and North America collapsed following neoliberal globalization in the late 1970s.

The globalization and automation of the bicycle industry make bikes less sustainable. First, they introduce extra emissions for transportation (from raw materials, components, and bicycles) and for producing and operating robots and other machinery. Second, producing steel, aluminum, carbon fiber composites, and electricity is more energy and carbon-intensive in China and other bike-producing countries than in Europe and North America. ¹⁰ Most importantly, however, is that large-scale automated production represents sunk capital that needs to be working most of the time to spread overhead costs, driving overproduction. ³

How long bicycles last

How much energy and other resources it takes to build a bicycle and to deliver it to a cyclist is just half the story. At least as importantly is how long the bike lasts. The shorter its lifetime, the more vehicles need to be produced over the lifetime of a cyclist, and the higher the resource use becomes.

For a long life expectancy, some parts of a bicycle need replacement. These are typically smaller parts such as shifters, chains, and brakes. ¹¹ Until a few decades ago, component compatibility was a hallmark of bicycle manufacturing. ¹² My bicycles are a perfect example of this. Most components – such as wheels, gear set, and brakes – are interchangeable between the different frames, even though every vehicle is from another brand and year of construction. Component compatibility allows for easy maintenance and repairability, thereby increasing the lifetime of a bicycle. Bike shops in even the smallest villages can repair all types of bicycles using a limited set of tools and spare parts. ¹² Cyclists can do minor repairs at home.

Unfortunately, compatibility is hardly a feature of bicycle manufacturing anymore. Manufacturers have introduced an increasing number of proprietary parts and keep changing standards, resulting in compatibility issues even for older bicycles of the same brand. ¹³ For example, if the shifter of a modern bike breaks after some years of use, a replacement part will probably no longer be available. You need to order a new set from a new generation, which will be incompatible with your front and rear derailleur – which you also need to replace. ¹² For road bikes, the change from cassette bodies with ten sprockets (around 2010) to cassette bodies with eleven, twelve, and most recently thirteen sprockets have made many wheelsets obsolete, and the same goes for the rest of the drivetrain including shifters and chains. ¹²¹

Before the 1980s, most bicycle components were interchangeable between frames of different brands and generations.

Disc brakes, which are now on almost every new bicycle, all have different axle designs, meaning that every vehicle now requires proprietary spare parts. ¹ Disc brakes also required new shifters, forks, framesets, cables, and wheels, making such bicycles incompatible with earlier designs. ¹² The rise of proprietary parts makes it increasingly hard to keep a bike on the road through maintenance, reuse, and refurbishment. As the number of incompatible components grows, it becomes impossible for bike shops to have a complete stock of spare parts. ¹²

Component incompatibility is accompanied by decreasing component quality. An example is the saddle, which hardly ever outlasts a frameset because it cracks at the bottom of the shell. ¹² A little extra material would make it last forever – as proven by all saddles of my 40 to 50-year-old road bikes. Low quality affects some parts of expensive bicycles but is especially problematic for cheap bicycles made entirely of low-quality components. Cheap bicycles – bike mechanics refer to them as “built-to-fail bikes” or “bike-shaped objects” – often have plastic parts that break easily and cannot be replaced or upgraded. These vehicles typically last only a few months. ¹³¹⁴

Illustration: [Diego Marmolejo](https://www.instagram.com/ddidak/).

How bicycles are powered

So far, we have only dealt with entirely human-powered bicycles, but bikes with electric motors are becoming increasingly popular. The number of e-bikes sold worldwide grew from 3.7 million in 2019 to 9.7 million in 2021 (10% of total bike sales and up to 40% in some countries like Germany). Electric bikes reinforce both trends that make bicycles less sustainable. On the one hand, electric motors and batteries require additional resources such as lithium, copper, and magnets, increasing the energy use and emissions of bike manufacturing. Researchers have calculated the greenhouse gas emissions caused by manufacturing an aluminum e-bike at 320 kg. ⁸ This compares to 212 kg for the production of an unassisted aluminum bicycle and 35 kg for an unassisted steel bicycle.

On the other hand, the life expectancy of an electric bicycle is shorter than that of an unassisted two-wheeler because it has more points of failure. The breakdown of the extra components – motor, battery, electronics – leads to a shorter lifecycle due to component incompatibility. An academic study on circularity in the bike manufacturing industry observes a significant increase in defective components compared to unassisted bicycles and concludes that “the great dynamics of the market due to regular innovations, product renewals, and the lack of spare parts for older models make the long-term use by customers much more difficult than for conventional bicycles.” ¹⁵

Electric bikes reinforce both trends that make bicycles less sustainable.

On top of this, electric bicycles require electricity for their operation, further increasing resource use and emissions. This impact is relatively small when compared to the manufacturing phase. After all, humans provide part of the power, and the electricity use of an electric bike (25 km/h) is only around 1 kilowatt-hour per 100 km. The average greenhouse gas emission intensity of electricity generation in Europe in 2019 was 275 gCO2/kWh. ¹⁶ If an e-bike lasts 15,000 km, charging the battery only adds 41 kg of CO2, compared to 320 kg for producing the (aluminum) bicycle. Even in the US and China, where the carbon intensity of the power grid is 50-100% higher than the European value, electric bicycle production dominates total emissions and energy use.

Cargo cycles

Combining energy-intensive materials, short lifetimes, and electric motor assistance can increase lifecycle emissions to surprising levels, especially for cargo cycles. These vehicles are larger and heavier than passenger bicycles and need more powerful motors and batteries. There are very few life cycle analyses of cargo cycles. However, a recent study calculated the lifecycle emissions of a carbon fiber electric cargo cycle to be 80 gCO2 per kilometer – only half those of an electric van (158 gCO2/km). ¹⁷ The researchers explain this by the difference in lifetime mileage – 34,000 km compared to 240,000 km for the van – and the carbon fiber composites in many components, including the chassis of the vehicle. The lifecycle emissions of the cargo cycle, including the electricity used to charge its battery, amount to 2,689 kg. That is almost 40 times the lifecycle emissions of two steel bicycles (each with a 15,000 km lifecycle mileage).

Extending the useful life of electric bicycles has less impact on lifecycle emissions when compared to unassisted bikes. That’s because the battery needs to be replaced every 3 to 4 years and the motor every ten years, which adds to the resource use of spare parts. ¹¹ This is demonstrated by a life cycle analysis of an electric steel cargo cycle with an assumed life expectancy of 20 years. ¹⁸ During its lifetime, the vehicle uses five batteries (each weighing 8,5 kg), two motors, and 3.5 sets of tires. Most lifecycle emissions are caused by these spare parts, with the batteries alone accounting for 40% of the total emissions. In comparison, the emissions for the steel frame are almost insignificant. ¹⁸ This particular cargo cycle was built for African roads and is not entirely representative of the average cargo cycle, mainly because of its heavy tires.

Cargo cycles have another disadvantage. Passenger bicycles and cars usually carry only one person, meaning that one passenger kilometer on a bike roughly equals one passenger kilometer in an automobile. However, for cargo, the comparison of ton-kilometers is more complicated. If the load is relatively light – usually up to 150 kg – the electric cargo cycle will be less carbon-intensive than a van. However, heavier loads require several cargo cycles to replace one van, which multiplies the embodied emissions. ¹⁸ Switching to cargo cycles without significantly reducing the cargo volume is unlikely to save emissions. Obviously, cargo cycles with steel frames and without electric motors and batteries – for now still the majority – will have much lower carbon emissions over their lifetimes.

How bicycles are used

In recent years, many cities have introduced shared bicycle services. In theory, shared bicycles could lower the number of bikes produced and thus decrease the environmental impact of bicycle production. However, building and operating bike-sharing services adds significant energy use and emissions. Furthermore, shared bicycles don’t last as long as privately owned bicycles. Consequently, shared bike services further reinforce the trends that make bicycles less sustainable.

A 2021 study compares the environmental impact of shared and private bicycles while including the infrastructure that each option requires. It concludes that personal bikes are more sustainable than shared bicycles. ⁸ The research is based on the Vélib system in Paris, France, which has 19,000 vehicles, roughly half with an electric motor. Vehicle manufacturing and bike-sharing infrastructure cause more than 90% of emissions and energy use. The remaining emissions are due to the construction of cycle lanes (3.5%), the rebalancing of the bicycles to keep all stations optimally supplied (2%), and the electricity used for charging the batteries of the electric bikes (0.3%). Altogether, a shared bicycle from the Vélib system has an emissions rate of 32g CO2/km, which is three to ten times higher than the rate of a personal bike (between 3.5 gCO2/km for a steel bicycle and 10.5 g CO2/km for an aluminum bicycle. ⁸

Building and operating bike-sharing services adds significant energy use and emissions

The scientists found that the bike-sharing service led to a 15% drop in bike ownership. However, they also calculated that the average lifespan of a shared bicycle is only 14.7 months, with an average lifetime mileage of 12,250 km. In comparison, the average lifetime of a personal bike in France, based on a 2020 survey, is around 20,000 km – almost 50% higher than for shared bicycles. The Vélib system includes 14,000 bike-sharing stations with a total surface of 92,000 m2 and an estimated lifetime of ten years. Each of the 46,500 docks consists of 23 kg steel and 0.5 kg plastic. The power consumption of each bike-sharing station is around 6,000 kWh per year. Due to the high impact of the infrastructure, the lifecycle emissions of shared electric bikes are only 24% higher than those of shared non-electric vehicles. ⁸

The environmental footprint of bike-sharing systems can vary significantly between cities. A life cycle analysis of bike-sharing services in the US found carbon emissions of 65g CO2/km – twice as high as in Paris. ¹⁹ This is largely because the US systems rebalance the bicycles using diesel vans, while the French service employs electric tractors. The US study also looks at the newer generation of “dockless” bike-sharing services, which score even worse. Dockless shared bikes can be parked anywhere and located through a smartphone application. Although this removes the need for stations, each bicycle requires energy-intensive electronic components, and the system also generates emissions through communication networks. ¹⁹¹⁰ Furthermore, dockless systems require more bicycles and involve more rebalancing.

A life cycle analysis of Chinese bike-sharing services, many dockless systems, shows high damage rates and low maintenance rates for bicycles. The annual damage rate is 10-20% for reinforced bicycles and 20-40% for lighter vehicles which have become more common. In practice, a shared bicycle becomes scrap when the bike part with the worst durability breaks down. Repair is virtually not happening. ¹⁰ Finally, when the companies go bankrupt, bike sharing creates mountains of waste – including bicycles in good condition. ¹⁰ ¹

Image: Lifecycle carbon emissions per kilometre of riding a bicycle. Graph: Marie Verdeil. Data sources: [^8][^17][^19][^26].

Not every bicycle replaces a car

None of this should discourage cycling. Even the most unsustainable bicycles are significantly less unsustainable than cars. The carbon footprint for manufacturing a gasoline or diesel-powered car is between 6 tonnes (Citroen C1) and 35 tonnes (Land Rover Discovery). ²⁰ Consequently, building one small automobile such as the C1 produces as many emissions as making 171 steel bicycles or 28 aluminum bicycles. Furthermore, cars also have a high carbon footprint for fuel use, while bikes are entirely or partly human-powered. ²¹ Electric cars have higher emissions for production but lower emissions for operation (although that depends entirely on the carbon intensity of the power grid).

The bicycle even holds its advantage when its much shorter lifetime mileage is taken into account. ²² Gasoline and diesel-powered cars now reach more than 300,000 km, double their lifetime in the 1960s and 1970s. ²³ If a bicycle lasts 20,000 km, it would take 15 bikes to cover 300,000 km. If those are steel bicycles without an electric motor, the total carbon footprint for manufacturing is still six times lower than for a small car: 1,050 kg of CO2. If the bikes are made from aluminum and have electric motors, then emissions grow to 4,800 kg CO2, still below the manufacturing carbon footprint of the small car.

However, not every bicycle replaces a car. That is especially relevant for shared and electric bikes: studies show that they mainly substitute for more sustainable transport alternatives such as walking, using an unassisted or private bicycle, or traveling on the subway. ¹⁹ ²⁴ In Paris, shared bikes have three times higher emissions than electric public transportation. ⁸ In addition, many carbon-intensive bicycles are bought for recreation and are not meant to replace cars at all – they may even involve more car use as cyclists drive out of town for a trip in nature. In all those cases, emissions go up, not down.

How to make bicycles sustainable again?

In conclusion, there are several reasons why bicycles have become less sustainable: the switch from steel to aluminum and other more energy-intensive materials, the scaling up of the bicycle manufacturing industry, increasing incompatibility and decreasing quality of components, the growing success of electric bicycles, and the use of shared bike services. Most of these are not problematic in themselves. Rather, it’s the combination of trends that leads to significant differences with bicycles from earlier generations.

For example, based on data mentioned earlier, manufacturing an electric bicycle made from steel would have a carbon footprint of 143 kg. Although that is four times the emissions from an unassisted steel bicycle, it is below the carbon footprint of an aluminum bicycle without an electric motor (212 kg). Especially if the battery is charged with renewable energy, riding an electric bike can thus be more sustainable than riding one without a motor. Likewise, an aluminum bicycle with a long life expectancy – for example, through component compatibility – could have a lower carbon footprint than a steel bicycle with a more limited lifespan.

Many researchers advocate switching back to producing bicycles from steel instead of aluminium and other energy-intensive materials. That would bring significant gains in sustainability for a relatively low cost – slightly heavier bicycles. Steel frames would also make electric and shared bikes less carbon intensive. Some researchers promote bamboo bike frames, but the benefit compared to old-fashioned steel or even aluminium frames is unclear. ²⁵ A “bamboo bicycle” still requires wheels and many other parts made out of metal or carbon fibre composites, and the frame tubes are usually held together by carbon fibre or metal parts. ⁶ Furthermore, the bamboo is chemically treated against decay and becomes non-biodegradable. ¹

Reverting to local and less automated bike manufacturing is a requirement for sustainable bicycles.

Better component compatibility would increase the life expectancy of bicycles – also electric ones – through repair and refurbishment. It would bring no disadvantages for consumers, even on the contrary. However, unlike a switch to steel frames, better component compatibility would hurt the sales of new bicycles. A study concludes that “the abandonment of standardization is a profitable business model because it ensures that bicycles can only be ridden for so long.” ¹ The decreasing sustainability of bikes is not a technological problem, and it’s not unique to bicycles. We also see it in manufacturing other products, such as computers. One bike mechanic observes: “The problem here is capitalism; it’s not the bikes.” ¹⁴

Reverting to local and less automated bike manufacturing is a requirement for sustainable bicycles. The main reason is not the extra energy use generated by transportation and machinery, which is relatively small. For example, shipping from China adds around 0.7 to 1.2 gCO2/km for shared bicycles. ⁸ More importantly, domestic and manual bike manufacturing is essential to make repair and refurbishment the more economically attractive option. By definition, repairing is local and manual, so it quickly becomes more expensive than producing a new vehicle in a large-scale, automated factory. ¹⁰ Locally made bicycles would increase the purchase price for consumers. However, better repairability would allow for a longer life expectancy and a lower cost in the long term. Addressing bike theft and parking problems is also essential because they are often a reason for buying cheap, short-lasting bicycles. ²⁶

Finally, shared bicycle services can have their place, and we will probably see further improvements in their resource efficiency – the newest bike-sharing stations in Paris have reduced their power consumption by a factor of six. ⁸ However, shared bicycles are unlikely to become more sustainable than private bicycles because they always require rebalancing and a high-tech infrastructure to make the service work. Furthermore, getting attached to your bike can be a strong incentive to take care of it well and thus increase its life expectancy, as I can testify.

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US petition that calls for end o built to fail bikes gaining support in BC. https://vancouversun.com/news/local-news/u-s-petition-that-calls-for-end-of-built-to-fail-bikes-gaining-support-in-b-c ↩︎
Aaron Gordon. “Mechanics Ask Walmart, Major Bike Manufacturers to Stop Making and Selling ‘Built-to-Fail’ Bikes”, Vice, January 13, 2022. https://www.vice.com/en/article/wxdgq9/mechanics-ask-walmart-major-bike-manufacturers-to-stop-making-and-selling-built-to-fail-bikes ↩︎ ↩︎
Koop, Carina, et al. “Circular business models for remanufacturing in the electric bicycle industry.” Frontiers in Sustainability 2 (2021): 785036. https://www.frontiersin.org/articles/10.3389/frsus.2021.785036/full ↩︎
https://www.eea.europa.eu/data-and-maps/indicators/overview-of-the-electricity-production-3/assessment ↩︎
Temporelli, Andrea, et al. “Last mile logistics life cycle assessment: a comparative analysis from diesel van to e-cargo bike.” Energies 15.20 (2022): 7817.. https://www.mdpi.com/1996-1073/15/20/7817 ↩︎
Schünemann, Jaron, et al. “Life Cycle Assessment on Electric Cargo Bikes for the Use-Case of Urban Freight Transportation in Ghana.” Procedia CIRP 105 (2022): 721-726. https://www.sciencedirect.com/science/article/pii/S2212827122001214 ↩︎ ↩︎ ↩︎
Luo, Hao, et al. “Comparative life cycle assessment of station-based and dock-less bike sharing systems.” Resources, Conservation and Recycling 146 (2019): 180-189. https://www.sciencedirect.com/science/article/abs/pii/S0921344919301090 ↩︎ ↩︎ ↩︎
https://www.theguardian.com/environment/green-living-blog/2010/sep/23/carbon-footprint-new-car ↩︎
Bicycles are entirely or partly powered by food calories. Some people argue that the life cycle energy requirements of bicycles are higher than other modes, when one considers the impact of food require to provide additional calories that are burned during the bicycle use. However, the majority of people in car-centered societies take in more calories than their sedentary lifestyle requires. Increased cycling would lead to lower obesity rates, not to higher calorie intakes. ↩︎
This a purely theoretical calculation, because cars encourage much longer trips than bicycles. ↩︎
Ford, Dexter. “As Cars Are Kept Longer, 200,000 Is New 100,000.” New York Times, March 16, 2012. https://www.nytimes.com/2012/03/18/automobiles/as-cars-are-kept-longer-200000-is-new-100000.html?_r=2&ref=business&pagewanted=all& ↩︎
Zheng, Fanying, et al. “Is bicycle sharing an environmental practice? Evidence from a life cycle assessment based on behavioral surveys.” Sustainability 11.6 (2019): 1550. https://www.mdpi.com/2071-1050/11/6/1550 ↩︎
A comparison of the life cycle emissions of a bamboo versus an aluminium bicycle showed little difference (233 vs. 238 kg CO2). [6] ↩︎
Larsen, Jonas, and Mathilde Dissing Christensen. “The unstable lives of bicycles: the ‘unbecoming’of design objects.” Environment and Planning A: Economy and Space 47.4 (2015): 922-938. https://orca.cardiff.ac.uk/id/eprint/131212/1/M%20Christensen%202015%20the%20unstable%20lives%20of%20bicycles%20ver2%20postprint.pdf ↩︎