For the 25-year period between 1990 and 2014, U.S. greenhouse gas (GHG) emissions from the transportation sector rose from 24.4% of total GHG emissions to 26.6%. In contrast, emissions from the industrial sector fell from 35.6% of total emissions to 29.4%. Emissions in the commercial, residential and agricultural sectors also rose during the period.

The rise in GHG emissions was not spread evenly throughout the transportation sector. Emissions from cars and light trucks fell from 63.8% of total sector emissions to 60.7%. Commercial aircraft cut emissions from 7.1% of the sector total to 6.4%, measured on domestic flights only. Medium- and heavy-duty trucks, however, posted an increase in sector emissions from 14.9% in 1990 to 22.5% in 2014.

The data were reported Monday by University of Michigan Transportation Research Institute researchers Michael Sivak and Brandon Schoettle.

GHG emissions from cars and light trucks also rose as a percentage of total emissions, from 15.6% in 1990 to 16.1% in 2014. And as a percentage of all GHG emissions, medium- and heavy-duty truck emissions rose from 3.6% of the 1990 total to 6.0% of the total in 2014.

Sivak and Schoettle noted the implications of the study:

There are two main implications of this study. First, because of the major progress in reducing emissions from industry during the period examined, we can expect an increased emphasis on reducing emissions from the other economic sectors, including transportation. Second, because of the large increase in the contribution of medium- and heavy-duty trucks to total emissions, we can expect an increased emphasis on reducing emissions from these classes of vehicles.

A couple of our own observations: in 1990, coal generated more than 50% of U.S. electricity compared with just 32% this year. Natural gas, which emits roughly half as much GHG as coal, has jumped from around 12% of power generation to 33% in the same period. According to the U.S. Energy Information Administration, coal-fired generation’s share of total U.S. electricity generation plummeted from 39% in 2014 to 28% in the first four months of 2016.

Low prices for crude oil and gasoline are working against the transportation industry’s efforts to reduce GHG emissions. Large sport utility vehicles and full-size pickups are selling at high levels, and although they operate more cleanly than in the past, they simply burn more fuel.

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