Every time you face traffic jams in the morning and evening rush hours, are you thinking that it would be better if more people ride bicycles to work? "Okay, how much better?" More and more countries have legally pledged to achieve zero net carbon emissions by 2050, and the UK is one of them.
Although we have made progress in some areas, emissions from transportation continue to rise. If we do not change the way in our life, we cannot reach net zero. So, is cycling part of the solution?
To understand the potential impact of cycling on a sustainable future, we must answer two key questions:
1. What is the carbon cost of cycling? How does it compare to other means of transportation?
2. Will the dramatic increase in cycling have an impact on our carbon footprint?
The study found that the carbon footprint of cycling is about 21 grams of carbon dioxide per kilometer. This is less than walking or taking a bus, and the emissions are less than one-tenth of driving.
About three-quarters of bicycle greenhouse gas emissions occur when the extra food needed to produce "fuel" bicycles, the rest comes from making bicycles
The carbon footprint of electric bicycles is even lower than that of traditional bicycles because although battery manufacturing and electricity use produce emissions, they burn fewer calories per kilometer
How environmentally friendly is the bicycle as a mode of transportation?
In order to compare the emissions of carbon fibre bicycles and other vehicles, we need to calculate the total amount of greenhouse gas emissions per kilometer.
This requires a life cycle analysis. Life cycle assessment is used to compare the emissions of various products, from power plants to gaming consoles.
Their working principle is to add up all emission sources during the product's entire life (production, operation, maintenance, and disposal) and divide by the useful output that the product can provide during its life.
For a power station, this output may be the total amount of electric energy it produces during its life; for a car or a bicycle, it is the number of kilometers traveled. In order to calculate the emissions per kilometer of bicycles for comparison with other modes of transportation, we need to know:
Greenhouse gas emissions related to bicycle manufacturing and processing. Then divide by the average number of kilometers between production and processing.
The emissions generated by the extra food produced per kilometer provide fuel for cyclists. This is done by calculating the extra calories required per kilometer cycle and multiplying it by the average food production emissions per calorie produced.
It is worth acknowledging that the previous method is too simple due to the following reasons.
First, it assumes that every additional calorie consumed is another calorie consumed through diet. But according to this review article entitled "The Effects of Exercise on Food Intake and Body Obesity: A Summary of Published Research", when people burn more calories through exercise, they usually don’t consume as many calories in their diet...
In other words, they lose weight by lacking calories. Therefore, this analysis may overestimate the food emissions of bicycles.
Second, it assumes that people do not change the type of food during exercise, only the quantity. Different foods have very different effects on the environment.
At the same time, it does not take into account that if people ride bicycles more often, they may take more baths, wash more clothes, or spend more money on other polluting activities (what environmentalists call the Rebound effect).
What is the environmental cost of making a bicycle?
Making bicycles requires a certain amount of energy, and pollution will inevitably occur.
Fortunately, a lot of work has been done in this study entitled "Quantifying Bicycle CO2 Emissions" conducted by the European Bicycle Federation (ECF).
The author uses data from a standard database called ecoinvent, which classifies the supply chain environmental impact of various materials and products.
From this, they calculated that manufacturing a Dutch commuter bicycle with an average weight of 19.9 kg and mainly made of steel would result in 96 kg of carbon dioxide emissions.
This figure includes manufacturing spare parts required throughout its life. They believe that the emissions from the disposal or recycling of bicycles are negligible.
CO2e (CO2 equivalent) refers to the total global warming potential of all greenhouse gases (including CO2, methane, N2O, etc.) emitted, expressed as the pure CO2 mass required to cause the same amount of warming in a 100-year period.
Material issues
According to data from the World Steel Association, for every kilogram of steel produced, an average of 1.9 kilograms of carbon dioxide is emitted.
According to the report "Environmental Overview of Aluminum in Europe", for every kilogram of aluminum produced, an average of 18 kilograms of carbon dioxide is released, but the carbon cost of recycling aluminum is only 5% of the raw material.
Obviously, the emissions from the manufacturing industry vary from material to material, so the emissions from the manufacturing industry also vary from bicycle to bicycle.
The Duke University report estimates that the production of aluminum alloy-specific Allez road frames alone generates 250 kg of carbon dioxide emissions, while the carbon fiber-specific Rubaix frame generates 67 kg of carbon dioxide emissions.
The author believes that the heat treatment of high-end aluminum frame bike greatly increases the energy demand and carbon footprint of the manufacturing industry. However, the author points out that this study may have considerable inaccuracies. We have asked the authors and expert representatives of this study to elaborate on this, but have not yet received a reply.
Because these numbers may be inaccurate and do not represent the entire bicycle industry, we will use the European Economic Cooperation Organization (ECF) estimated carbon dioxide emissions per bicycle to be 96 kg, but be aware that the carbon footprint of each bicycle may be a very big difference.
Of course, greenhouse gases are not the only problem in making bicycles. There is also water pollution, air particle pollution, landfills, etc., which will cause other problems besides climate change. This article only focuses on the impact of cycling on global warming.
Manufacturing emissions per kilometer
ECF further estimates that the average life span of a bicycle is 19,200 kilometers.
Therefore, if the 96 kilograms of carbon dioxide emissions required to manufacture a bicycle are distributed within a range of 19,200 kilometers, then the manufacturing industry will emit 5 grams of carbon dioxide per kilometer.
What is the carbon cost of the food needed to produce one kilometer?
ECF calculated that cyclist averages 16 kilometers per hour, weighs 70 kilograms, and consumes 280 calories per hour, while if they don’t ride a bicycle, they burn 105 calories per hour. Therefore, a cyclist consumes an average of 175 calories per 16 kilometers; this is equivalent to 11 calories per kilometer.
How many calories does cycling burn?
To convert this into emissions per kilometer, we also need to know the average greenhouse gas emissions per calorie of food produced. Emissions from food production take many forms, including land-use changes (such as flooding and deforestation), fertilizer production, livestock emissions, transportation, and cold storage. It is worth pointing out that transportation (food miles) only accounts for a small part of the total emissions from the food system.
In general, it is very desirable to reduce carbon emissions by riding a bicycle.
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Post time: Jul-22-2021