By Eric Murphy
Advances in technology have made transportation more energy efficient in recent decades, lowering emissions per mile and per unit of freight. But according to a new study, those efficiency gains haven’t been enough to offset the rise in emissions from new transportation demand. To hold transportation emissions steady going forward, the study says, global transportation demand must not continue rising, or we must make a more dramatic shift toward electrification than currently imagined.
Based on our analysis, 14 states are on track to lower transportation emissions by 10% or more in the coming years. Those numbers fall short of most targets, but are still progress compared to past trends. However, there are 25 states where emissions are still increasing, some by as much as 15%, and rising transportation demand is likely a major factor.
First, the study’s good news: over a long historical period, the transportation sector has become significantly more efficient in two different ways. First, the efficiency of converting fuel into “useful energy” has improved, with less lost as heat, vibration, or other wasteful outputs. Second, the efficiency of converting that useful energy into transportation services has also improved, reducing the amount of “useful energy” needed to move one person one mile, on average. The result is thousands of gigatons of CO2 avoided.
But the study’s authors note:
These gains have not been sufficient to offset the growing demand for transport. Historical energy transitions in the transport sector have consistently resulted in increased final energy consumption, regardless of improvements in final-to-useful efficiency…. For future policies to succeed in reducing CO2 emissions, either technological improvements should increase drastically to match the demand growth, or policies should start prioritizing demand-side factors, namely in reducing individual transport demand.
That demand is, “the primary upward driver of emissions,” notes the study. Not only is travel increasing, but there has been a swing toward more carbon-intensive travel modes like road and air travel. What’s worse, explain the authors, that growing transportation system is also facing diminishing returns, with each additional unit of transportation activity yielding progressively smaller economic impacts.
Mounting evidence suggests we cannot tackle emissions without managing demand effectively, as outlined our guide, Modernizing Mitigation. Without demand-side interventions, says the study, a dramatic shift in energy supply to electricity would need to occur in transportation. Assuming the continuation of current trends, 52% of all transportation sector energy would need to come from electricity by the end of the decade to keep emissions at their 2020 levels.
Photo Credit: Ahmer Kalam via Unsplash. License.