Transportation Sector Greenhouse Gas Emissions Top Power Generation

Transportation Sector Greenhouse Gas Emissions Top Power Generation

The U.S. EPA released a new report detailing national greenhouse gas (GHG) emission sources on April 11 — just in time to deliver some important news ahead of Earth Day. For the first time in recent history, GHG emissions from US transportation (sources like cars, trucks, and planes) exceed GHG emissions from the generation of US electric power. The recent trends speak to continuing improvements in the power sector and challenges ahead for the transportation and vehicle fuel sectors.

GHG Emissions Allocated to US Economic Sectors. 2017 marked a transition where transportation sources now emit more GHG than electricity producers in the US.

Power Was Fueled for Reductions

 Despite significantly more electricity being demanded and delivered in 2017 than in 1990 (the baseline year for EPA’s study), the US power sector’s GHG emissions in 2017 were well below 1990 levels. Up until only several years ago, coal combustion was the dominant source of the power sector’s GHG emissions. When coal is burned, roughly twice the amount of GHG is released compared to natural gas combustion. Thus, along with the relatively recent prolific availability of natural gas and the switch at many power plants to that fuel from coal, came a steady decline in power’s GHG emissions. Renewable generation has been growing in recent years as well, contributing to the GHG reduction trend, but the switch from coal to gas was a major factor in reducing GHG emissions from electricity generation.

Electric Power Generation and GHG Emissions. Growth in natural gas-based power and reduction in coal-based power has led to substantial reduction in power generation GHG emissions.

While broad transition to a readily-available, less carbon-heavy fuel has enabled the power sector to meet demand while emitting less, transportation has yet to undergo such a sector-wide shift.

Transportation Has Miles to Go

 While electrification of transportation may shift GHG emissions back to the power sector, taking the road that power traveled and focusing on fuel carbon content may get the GHG reduction wheel turning for the transportation sector. EPA’s analysis showed that passenger cars were the largest source of US transportation’s GHG emissions (41.4%), and since passenger cars in the US run predominantly on gasoline, increased renewable fuel volume obligations for gasoline (i.e., blending a fuel like corn-based ethanol with the gasoline before it gets to the pump) are likely in store during the next phase of GHG reduction policies in some areas.

Fuels Used in Transportation Sector and Total Sector GHG Emissions. Gasoline-powered vehicles are the largest source of GHG emissions in Transportation.

A drop and flat-line rate in vehicle miles traveled (VMT) from 2007 to 2012 seems to coincide with a spike in gas prices during that period, which in turn led to a substantial reduction in annual transportation GHG emissions.  However, as gas prices normalized, VMT and subsequent GHG emissions are once again trending upward.

Policies to decarbonize transportation are gaining attention in states whose governors have committed to the Paris Climate Accord (US Climate Alliance States), with significant policy development activity already occurring in the northeast and mid-Atlantic states where a regional project called the Transportation Climate Initiative (TCI) has been gaining traction.

A potential acceleration of renewable fuel volume obligations could mean the potential for increased compliance and reporting requirements by US petroleum providers and refineries, carbon offset expenditures within the Transportation sector, and fuel supply logistics challenges for entire regions (like TCI states) that may hold to an interstate fuel standard.

GHG Reduction during GDP Acceleration

 Yet despite the challenges facing the transportation sector to realize the same level of reductions that the power sector has seen in recent years, total US GHG emissions have been dropping in recent years and are nearing 1990 levels, which is a substantial note given the more than tripling growth the US economy has undergone from 1990 to 2017, and that’s something to honk your horn about.

Cumulative Change in Annual Gross US GHG Emissions Relative to 1990 (1990=0). Recent trend in US GHG emissions is nearing 1990 levels.

Source of all charts: US EPA Inventory of US Greenhouse Gas Emissions and Sinks 1990-2017 (EPA 430-R-19-001).

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Meteorologist, Project Manager
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