Abstract
Reducing motorized transport and increasing active transport (i.e. transport by walking, cycling and other active modes) may reduce greenhouse gas (GHG) emissions and improve health. But, active modes of transport are not zero emitters. We aimed to quantify GHG emissions from food production required to fuel extra physical activity for walking and cycling. We estimate the emissions (in kgCO2e) per kilometre travelled for walking and cycling from energy intake required to compensate for increased energy expenditure, and data on food-related GHG emissions. We assume that persons who shift from passive modes of transport (e.g. driving) have increased energy expenditure that may be compensated with increased food consumption. The GHG emissions associated with food intake required to fuel a kilometre of walking range between 0.05 kgCO2e/km in the least economically developed countries to 0.26 kgCO2e/km in the most economically developed countries. Emissions for cycling are approximately half those of walking. Emissions from food required for walking and cycling are not negligible in economically developed countries which have high dietary-related emissions. There is high uncertainty about the actual emissions associated with walking and cycling, and high variability based on country economic development. Our study highlights the need to consider emissions from other sectors when estimating net-emissions impacts from transport interventions.
Highlights
Reducing motorized transport and increasing active transport may reduce greenhouse gas (GHG) emissions and improve health
Based on the average global diet[18], emissions required for walking are up to 0.11 kgCO2e/km (95% uncertainty interval (UI) 0.05 to 0.22)) and up to 0.14 kgCO2e/km (95% UI 0.06 to 0.28)) for cycling when energy expenditure is fully compensated with increased energy intake (Fig. 1)
We estimate that 57% of additional energy expenditure was compensated with additional food intake in the cohort study reported by Martin et al (2015), with a range of 19% to 96% based on the confidence interval around the reported change in body mass index (BMI)
Summary
Reducing motorized transport and increasing active transport (i.e. transport by walking, cycling and other active modes) may reduce greenhouse gas (GHG) emissions and improve health. We estimate the emissions (in kgCO2e) per kilometre travelled for walking and cycling from energy intake required to compensate for increased energy expenditure, and data on food-related GHG emissions. Reducing motorized transport and increasing active transport (i.e. active modes of transport such as walking and cycling) may both reduce GHG emissions and improve population health. Mode shift from passive to active forms of transport has been associated with reductions in body mass index (BMI)[5,10,11] These longitudinal studies do not include comprehensive assessments of all changes in individual circumstances that may confound the observed relationship. Meta-analysis of laboratory studies show that individuals tend not to compensate for increased energy expenditure from exercise in the immediate hours after exercise[13], the extent and nature of compensation for increased energy expenditure from physical activity in the longer term is not well established[12]
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