Transportation isn’t the only sector that contributes to greenhouse gas emissions in our world, but it’s a big chunk, and it’s portion is growing.
Michael Sivak and Brandon Schoettle, from the University of Michigan, took a look at the numbers and discovered that transportation, both personal and commercial, is likely to be the next sector in the sights of anti-emissions law.
As you can see from the chart, industry started out as the worst offender by far, but decreased the most. Despite a growth in GDP in the U.S. over the same period, industrial emissions decreased by 11% in the quarter-century covered by the study. This is in part thanks to a real reduction in emissions from industry, and also because transportation has grown as a source of pollution. Remember, these are percentages, so if one goes up, the others must go down.
To see how transportation emissions have grown, take a look at this chart, which shows the emissions of various transportation modes as percentages of all emissions.
Passenger vehicles and light-duty trucks saw a spike in the early 2000s, but have steadily decreased since then, dropping back almost to 1990 levels (16.1% today vs. 15.6% in 1990). These vehicles still account for almost all (60.7% in 2014) of transport emissions, though. Commercial aircraft have stayed almost the same throughout the period, making up just 1.7% of total emissions today. The biggest growth in transport emissions is from medium to big trucks.
That’s no surprise. According to from the U.S. Department of Transportation, trucks make up just 1% of traffic, but create more than a quarter of all road pollution. Sivak and Schoettle’s study shows that relative emissions from medium-to-large trucks have almost doubled since 1990, from 3.6% to 6.0%. But even more striking is the absolute increase for these vehicles. During this period, greenhouse emissions for trucks grew a staggering 76.3%, while the overall emissions of the U.S grew just 7.3%.
Another factor is the increase in the number of vehicles. Even as cars and trucks are engineered to burn less fuel, we put more of them on the road. Today, there are a third more vehicles on our roads than in 1990.
Sivak and Schoettle conclude that transport will be the next big focus for emissions legislation, in part "because of the major progress in reducing emissions from industry." That is, industry has been forced to clean its act up so much that everyone else is starting to look bad. And that focus is likely to be on medium-to-large trucks, as those are the classes causing the most damage relatively.
But it’s not all bad news: Cargo transport is a ripe target. If we go back to that figure of trucks making up just 1% or traffic, and yet spewing out a quarter of all road pollution, then we see that we only have to target a relatively small number of vehicles (the U.S. has 4.3 million trucks on its roads) to make a big impact. Electrifying the roads is one option. Another is self-driving trucks that run way more efficiently than those driven by humans. But we need something, because trucks haul 70% of the country’s cargo, and that won’t change any time soon.
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