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More efficient cars may be one of the causes of increased greenhouse gas emissions from road travel

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Paul Anderson

6 July 2016

New computational modelling work suggests that, despite improving transport efficiency, the increasing accessibility and popularity of road travel is actually leading to higher levels of greenhouse gas emissions.

The research, carried out by University of Bristol Cabot Institute members Drs Rachel Freeman, Chris Preist and Mike Yearworth at the University of Bristol’s Systems Centre, focused on developing a new approach to a problem that has been identified by many but for which the causes are not very well understood - the ‘rebound effect’ or ‘Jevon’s paradox’.

Jevons’ Paradox suggests that more efficient technologies actually lead to increased usage of a resource. For example, modern lighting technologies have become over nine hundred times more efficient at converting energy to light, yet overall energy consumption for lighting has increased by forty times overall. The ‘cheaper’ a resource is to use, the more popular the technology becomes, eventually increasing demand and overall resource use.

Dr Freeman’s study indicates that in the past increased travel consumption completely offset any gains from more efficient vehicles and that this is likely to be true in future unless a systemic suite of interventions are introduced. To achieve the EU goals of a reduction in emissions of 40% by 2030 in the UK’s road transport system, there would need to be much greater increases in technological efficiency, costlier travel and significantly reduced travel consumption than are currently being planned for.

Commenting on the paper’s findings, the editors of the special edition, Suh et al., stated “it is a sobering observation that, although the potential reduction in GHG emissions and other environmental impacts through efficiency technologies can be substantial, efficiency technologies alone will not be able to meet the GHG emission targets considered in this special issue (Freeman et al. 2015; Taptich et al. 2015), calling for a concerted action involving multiple instruments to cope with climate change.”

Professor Richard Pancost, Director of the University of Bristol Cabot Institute, commented on the findings: “It is concerning to have even more evidence for the rebound effect. Nonetheless, it is vital to have this information and vital to include it in the narrative of how we decarbonise society. Understanding this allows us to address it.”

Further information

This research has been published in a special issue of the Journal of Industrial Ecology on the Environmental Impacts of Demand-Side Technologies and Strategies for Carbon Mitigation. This special issue was prepared in collaboration with the International Resource Panel (IRP) of the United Nations Environment Programme (UNEP), and several of the studies will serve as technical appendices to a forthcoming report on life cycle implications of energy efficiency technologies by the IRP. The special edition is available for a limited time as open source ( 

The Suh et al quote above is taken from: Suh S, Hertwich E, Hellweg S, Kendall A (2016) Life Cycle Environmental and Natural Resource Implications of Energy Efficiency Technologies. Journal of Industrial Ecology 20:218–222. doi: 10.1111/jiec.12435.

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