Digging into land freight

“Health and climate impacts of future U.S. land freight…” has a long backstory, full of moments that begin, “But wait...!” The tale begins with black carbon, a particle that warms Earth’s climate during its short atmospheric lifetime. Like many explorers’ journeys, it crosses some unexpected landscapes.
Digging into land freight

Health and climate impacts of future U.S. land freight…” has a long backstory, full of moments that begin, “But wait...!” Here’s the question Tami Bond was working on when this work started:  Black carbon is a component of particulate matter that warms Earth’s climate, but remains in the atmosphere for just a short time. If one could flip black carbon emissions OFF, the climate immediately warms a little less, complementing the reduction of greenhouse gas emissions. There are also health benefits, which people value even more. How might we do that? 

But wait! Although black carbon has a short lifetime in the atmosphere, its emitters have a long lifetime on Earth. Diesel engines are the major source of black carbon in the Western world. Once a vehicle is on the road, its lifetime emissions are probably fixed. Fang Yan modeled vehicle fleets around the world and their mitigation strategies. 

But wait! In the United States, freight delivery, not passenger transport, consumes most of the diesel fuel. Modelers of far-future emissions had not explored realistic growth rates of trucking. As economies grow, so does the consumption of goods. A reasonable view of the future demands projections of commodities in addition to population and income, but commodities. Will people buy coal, paper, or electronics? Steve Smith and Kathryn Daenzer, economic modelers, pitched in their expertise.  

But wait! Shipping is not all about trucks. Chris Barkan, director of RailTEC, told us how a spike in oil prices caused a rush for fuel-efficient rail transport, with consequent congestion. This event sparked the idea for work on “modal shift:” switching between rail and truck transport. Yanfeng Ouyang and Taesung Hwang, experts in logistics and networks, spent a couple of years piecing data together to understand how modal choice might respond to oil price. This work shows that fuel taxes would favor efficient transport modes and create observable improvements in air quality, climate and health—but only if we invest in infrastructure before it’s needed.

But wait! Trains and trucks may get goods to a region, but something else gets them to your office or home. Delivery trucks are often closer to people than long-haul freight; maybe they have a stronger effect on people’s health. The locations of those shipments and people are evolving. We needed to know not just what was being shipped, but where. Bumsoo Lee and Sungwon Lee, urban planners who think about spatial distribution, created projections of dozens of metropolitan areas under regular and compact growth. To our surprise, compact growth made only a small difference in overall health—most of the environmental and health damage came from emissions from long-haul freight. 

But wait… even when we thought the components were ready, they weren’t connected. That was Liang Liu’s challenge. Her student journey involved stretching out of her comfort zone to learn about models in different fields in order to synthesize the final impacts of this entangled system. Along the way, the integration shed new questions. How could we make a global vehicle fleet model represent U.S. freight?  How do shipment ton-miles translate into fuel use and emission distribution? How would urban development affect population? What policy scenarios should be considered? And how could we think about uncertainty in this big, messy system? 

A final “but wait” moment came when we found that we needed help to translate emission and location to health impact. Running atmospheric models once is time-consuming; it’s almost impossible to do many scenarios. Fortunately, Chris Tessum and Julian Marshall had anticipated this problem and invented a reduced-form air-quality model. 

Nearly 10 years, many collaborators, and buckets of patience after we started, we have an expanded appreciation for entangled human systems. Our work shows that improvements in air quality, climate, and health are possible; in fact, they are already happening because of incoming regulations. It also shows that society needs to think about major shifts and enabling infrastructure in the quest for sustainability, and that we as researchers need the methods—and patience—to describe those changes. 

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