Decarbonising urban transportation

The transportation sector is a major contributor to global greenhouse gas emissions, accounting for around one-quarter of current annual emissions. Surface transportation (passenger vehicles, buses, rail, and freight transportation) contributes 75% of total emissions, with the remaining 25% allocated equally between air and water transport. According to the recently released 5th Assessment Report of the IPCC (September 2013), the transportation sector is expected to grow significantly in future years, particularly in rapidly developing countries around the world, and will therefore be one of a few key drivers of increasing global warming. Unless there is a major political effort and consumer willingness to change current energy consumption patterns and travel modes over the next few decades, transport-related emissions are likely to double by 2050 relative to levels observed in 2010. Because of the contribution of transportation to climate change and its impact on urban air quality, a comparative assessment of potential carbon emission reductions and health benefits of reduced particulate matter emissions was undertaken considering several low carbon pathways for development of the urban road transport sector up to 2050. As a result, we conclude that aggressive changes will be needed to scale back future emissions by 20% (or more) compared to present day emissions. These changes will impact vehicle fuel economy (+50%), urban mobility patterns (lower private car demand and greater use of public transportation), choice of alternative fuels (less use of petroleum-based fuels and greater use of biofuels and electrons) and electricity generation mix (greater use of renewables, carbon capture technologies for limiting fossil fuel carbon emissions, and/or nuclear energy). Public acceptance is fundamental to bring about changes in consumer attitudes and behaviour. Given the long lead times required for research, development, demonstration and deployment of new technologies, the time to act is now if we are to limit the global mean surface temperature increase to within 2°C above preindustrial levels.