Greenhouse Gas Emissions from Transportation

By Thaddeus Rumple

Greenhouse gases (GHGs) trap heat in the atmosphere, making the planet warmer, as a whole. While some GHGs come from natural sources, almost all of the increase in greenhouse gases in the atmosphere over the last 150 years can be traced to human activities. The most important sources of GHG emissions from the United States are fossil fuels, which are burned for electricity, heat, and transportation.

GHGs are also removed from the atmosphere by human and natural activity. Human beings can encourage atmospheric GHG reductions by planting trees and encouraging other natural activities that remove them. Anything that removes them is referred to as a “GHG sink.”

Motor vehicles are
one of the greatest contributors
to American air pollution.

The United States Environmental Protection Agency (EPA) tracks total U.S. emissions, and publishes an annual report, the Inventory of U.S. Greenhouse Gases and Sinks, which can be found by visiting http://1.usa.gov/1uAwSli. This report provides the EPA’s estimates of the total national GHG emissions and removals associated with human activities across the United States.

According to the EPA, 28% of the United States’ GHG emissions were from transportation in 2012. The EPA says “Greenhouse gas emissions from transportation primarily come from burning fossil fuel for our cars, trucks, ships, trains, and planes. Over 90% of the fuel used for transportation is petroleum- based, which includes gasoline and diesel.”

By comparison, 32% of GHGs released in the United States were from electricity production, mostly by burning coal and natural gas. But the electric sector was the only one that had GHGs exceeding those of transportation. Industrial production of GHGs was only 20% of the total. Land use and forestry accounted for 15%, agriculture for 10%, and commercial and residential heating for 10%.

The EPA has this to say of the transportation sector:

The Transportation sector includes the movement of people and goods by cars, trucks, trains, ships, airplanes, and other vehicles. The majority of greenhouse gas emissions from transportation are CO2 emissions resulting from the combustion of petroleum-based products, like gasoline, in internal combustion engines. The largest sources of transportation-related greenhouse gas emissions include passenger cars and light-duty trucks, including sport utility vehicles, pickup trucks, and minivans. These sources account for over half of the emissions from the sector. The remainder of greenhouse gas emissions comes from other modes of transportation, including freight trucks, commercial aircraft, ships, boats, and trains as well as pipelines and lubricants.

Relatively small amounts of methane (CH4) and nitrous oxide (N2O) are emitted during fuel combustion. In addition, a small amount of hydrofluorocarbon (HFC) emissions are included in the Transportation sector. These emissions result from the use of mobile air conditioners and refrigerated transport.

GHG emissions from transportation have increased about 18% since 1990. This is quite a lot less than increases in other sectors, which have seen GHG emissions grow by about 5% per year over the same time. Over the last few years increases in GHG emissions have started to slow down. In 2012, GHGs for the United States actually showed a decline from the previous year. Part of the decrease was because of a shift from coal to natural gas as a fuel for electric production. Mild winter temperatures in 2012 also played a part.

Now, there are some vehicle purchasers who consider the current low prices for oil and gas and are willing to buy vehicles with reduced fuel economy. The underlying facts of the market do not support the view that low prices can continue for long. Automotive companies are building increasing numbers of electric vehicles (EVs), and that will have a growing influence on transportation GHG emissions. General Motors, Ford, BMW, and Volkswagen have all said they will be producing EVs in greater numbers.

People who drive EVs are very much inclined to prefer them, according to reports. This is true whether the car is a Tesla Model S or the sub-compact Smart electric drive, a product of Mercedes-Benz.

One thing that we might mention is that driving an EV reduces GHG emissions only if the electricity used to charge the car is from sources with low EV emissions. An electric vehicle charged with electricity purchased from hydro, wind, or solar plants has very little in the way of GHGs associated with it. But an EV that is charged with electricity from a coal-burning plant could have GHG emissions no better than a car powered by gasoline.

Aside from using more fuel-efficient personal road vehicles, we can reduce GHGs by moving to other means of transportation. Busses, trains, bicycles, and walking are all often better choices, when they are possible.