Transportation: What percent of greenhouse gas emissions come from personal vehicles?

Recently, someone said to me that cars are the greatest source of greenhouse gas emissions in the United States. They are not, but it is easy to see how many people believe that they are the greatest source. For example, take this quote from MIT Technology Review

The implication, as often interpreted, is that personal cars are the greatest source. That comment comes from this EPA chart showing the Transportation segment at 29%, just barely surpassing electricity generation (transportation passed electricity in 2017):

Let’s drill down into the Transportation segment. This yields an allocation of transport related producers per the EPA:

59% of the Transportation segment (29% overall) is due to light duty vehicles used for personal transportation and for business and government.

59% of 29% is 17.11% is due to all light vehicle use including business and government. The remaining 12% is a combination of medium duty trucks (like UPS vans), large semi trucks, aircraft, rail, ships and boats, and “other”.

I was not able to find an exact figure for the percent of light duty vehicles used for personal use versus business and government. A reasonable estimate (based on some numbers I found) is that 20-25% are for business and government and 75-80% are for personal use. Some personal use vehicles are used for business and some business vehicles are used for personal, non-business use. We would also need to know how many miles are driven, and the mileage estimates for each vehicle. As you can see, there is no exact number – just broad estimates.

Using those best guesses (75% figure), personally owned vehicles account for about 13% (less than 17%) of greenhouse gas emissions in the U.S. and are not the dominant source of greenhouse gas emissions.

Looking back at the top chart, you can see that industry (22%) and electricity (28%) are, combined, the largest segment, at 50%. A large part of the industry segment is private electricity generation – or thermal generation for processing steel, chemicals and so on – from natural gas, fuel oil and even coal – consequently, electricity/industrial generation is the dominant source of greenhouse gas emissions.

Switching the vehicle fleet from gas to electric, all else being equal, shifts the production of greenhouse gases from the vehicle segment to the electricity segment.

For example, if I were to replace my Honda Fit with an EV, on the surface it would appear to reduce my own greenhouse gas emissions from transportation to zero. But, my electric utility generates 56% of its electricity from burning coal and 14% from natural gas (total 70%). Thus, I would be outsourcing my greenhouse gas emissions to their coal and gas plants. The vehicle transportation segment would reduce its GHGs – and I could feel very virtuous – but in reality I would have shifted a large portion of my GHGs across the GHG ledger to the electrical power plants side. (It is possible that due to where I live within the utilities coverage area that more of my electricity comes from hydropower than coal/gas but I have no way of knowing – all we know is the percentage for the utility as a whole.)

In general, this should not be interpreted as saying EVs are worse for the environment. To the contrary, EVs are generally better, but be sure to understand the trade offs.

There are some locations including India, China and even some U.S. states, where EVs may be worse according to the MIT Technology Review article:

In parts of India and China with particularly dirty electricity systems, EVs may even generate more emissions than gas-fueled vehicles, says Emre Gencer, a research scientist who worked on the study.

U.S. utilities are rapidly decreasing their use of coal, almost entirely by converting to natural gas, which cuts GHGs in half (but still remaining high at about 1,000 pounds per MWH). Perhaps more significantly”. Compared to Q2 of 2018, total U.S. power generation fell by 4% in Q2 of 2019″. The reason for this drop is not specified but is presumably due to widespread energy efficiency measures. The combination of converting coal to natural gas and reduced demand for electricity has caused GHG production from electricity generation to drop by -40% since 2005. Some states such as Utah, Indiana, Delaware, Kentucky, New Mexico, Wisconsin and West Virginia, have almost all of their electricity produced by burning coal.

According to MIT Technology Review:

Currently, US carbon emissions per mile for a battery electric vehicle are on average only about 45% less than those from a gas-fueled vehicle of comparable size. That’s because fossil fuels still generate the dominant share of electricity in most markets, and the manufacturing process for EVs generates considerably higher emissions, mainly related to the battery production.

https://www.technologyreview.com/s/614728/why-the-electric-car-revolution-may-take-a-lot-longer-than-expected/

Compare that “45% less” to the use of hybrid vehicle versus EVs. The 2020 Ford Escape Hybrid boasts a rumored estimate of perhaps 42 mpg which is about 70% more than the 25 mpg of the vehicle it replaces. Official EPA mpg is not yet available. (The 45% figure includes lifetime vehicle manufacturing energy use and the 70% does not include that.)

For many consumers (depending on where they live), EVs will produce less GHGs than comparable gas vehicles but may be on par with new plug-in hybrid vehicles. But for most people, EVs are not zero emissions.

Vehicle Lifetime Energy Use

The energy used to manufacture a vehicle versus the energy the vehicle consumes during operation is surprisingly high – for some vehicles, about half the energy consumed during the vehicles lifetime is used during its manufacture. The higher percentage applies to fuel efficient cars that consume much less gasoline during their lifetime. Replacing an existing gas vehicle with a EV powered by coal generated electricity will likely have a much smaller GHG reduction than you are expecting, regardless of the type of vehicle and mileage.

For example, suppose you decide to switch to an EV. You either sell your vehicle (so someone else uses it to produce GHGs) or you junk it (throwing away the energy used to manufacture it originally).

Then, you switch to a new EV – which consumes significant energy in its manufacture, mostly fossil-fuel based – and plug it in to the electric utility’s coal or natural gas powered electricity to charge the battery.

Your carbon footprint did not go to zero – not even close to zero. Up to half your vehicle’s lifetime energy consumption is still coming from fossil fuels (used in manufacturing it) and a significant part of your electrical generation is generating GHGs. You are likely producing less than before but you have not gone to zero. The lifetime GHG emissions of your new EV may be (ought to be!) less than the gas vehicle it replaced.

So what should you do?

If you already drive a “fuel efficient” vehicle, your best choice regarding vehicle lifetime GHG emissions is to keep driving it as long as possible. For example, my real world Honda Fit mileage is in the 39 to 42 mpg range. From an environmental standpoint, I should keep driving this car as long as possible, rather than switch to an EV.

If you drive a vehicle that is not fuel efficiency, such as getting 20-25 mpg, it may make sense to upgrade to a newer hybrid vehicle that gets far better gas mileage when you need to replace the vehicle. Revisit the 2020 Ford Escape Hybrid example, above, to see how the hybrid’s high mpg and overall greenhouse gases may, in fact, be less than a pure EV. An EV may be an option depending on how you use this vehicle – if you need to tow a trailer cross country, an EV is likely to make travel more difficult due to charging requirements. If you primarily drive locally, the EV may be a good choice.

Another option is plug-in hybrids. These contain a gas motor and electric motors, plus a small capacity battery good for 20-30+ miles of operation. The battery may be charged by plugging into the electrical mains, or by the on-board motor. When used as a plug-in, this becomes a short range EV, operating entirely as an EV for local trips, but providing the range and convenience of gas vehicles for long distance travel. The hybrid features enable efficient, high mileage performance on the highways too.

My state seems to be headed towards a path to reduce personal vehicle GHG emissions by pushing consumers into electrical vehicles. Another state, California, has enacted a new rule that all new state government vehicles must be electric (except for public safety – why the exemption?). This new rule is poor economics (EVs are expensive relative to gas cars and hybrids), and may not produce much reduction in GHGs, per the analysis above.

What is important is to reduce CO2 emissions – and that can also be done with vehicles that get far greater mpg (such as hybrids) and replacing fossil-fueled based electricity and thermal generation with alternatives.

Practicing factfulness – and digging in to the data – shows us that what we think we know is often not correct. On the surface, EVs seem to be zero emissions – but the reality is a bit different.

I happen to think EVs are cool and would like to have one. However, by the numbers, directly switching to an EV at this time does not yield the results we are led to believe it delivers.

The best bet for most of us is to move towards efficient hybrid and plug-in hybrids – versus EVs. For some of us, depending on our requirements and how our electricity is generated, an EV may be appropriate. However, if we already drive a very fuel efficient vehicle then continuing to drive that vehicle for as many years as possible is likely to produce less overall, vehicle lifetime GHGs than switching to a new vehicle.

Your most effective strategy for reducing energy-related green houses is to

  1. Lead an efficient life, avoiding wasted activities, products and services.
  2. Insulate and seal your home to modern standards
  3. Install solar PV to generate electricity. Depending on where you live (relative to sunshine availability), this can cut your household’s delivered energy by a significant amount. If your utility is fossil-fuel based, then this will have a far bigger impact on GHG reduction that switching to an EV.
  4. Consider an EV for local area transportation especially if your electrical power comes from non-fossil fuel sources. Otherwise, the greenhouse gas reduction by switching to an EV may be little. Installing solar PV to charge your EV is expensive. A typical solar PV installation may produce 20-30 kwh per day to meet household needs. A typical EV battery pack is in the 60 to 100 kwh range, meaning a 50% charge is 30-50 kwh (plus add in more for inefficiency factors). You might have to double the size of your solar PV installation to support recharging the vehicle.

Note – we are currently installing solar PV at our house. We now live in an area that has good amounts of sunshine, with a south facing roof. This solar PV replaces the electricity generated by the local utility, which is 56% generated from coal-fired power plants (70% from coal or natural gas). We heat with wood pellets from a local source.

Without solar PV in operation (it is not yet hooked up), our home averages 10-14 kwh of electricity per day versus the average of 28 kwh of typical American homes. After solar PV comes online, our annual average should be about 0 kwh from the utility. Our installation uses “net metering”. During much of the year, our array produces more electricity than we need and this is sent back to the grid for use by someone else (thereby avoiding fossil-fuel generation). During a few winter months and especially on cloudy days, the array will produce less than our own demand. Excess power produced is banked as a credit to draw upon in winter when our home supplements the solar array by taking power from the grid. Excess power credits left over after 12 months are donated to charity and low income residents.

We are also upgrading the existing attic insulation. The existing insulation was probably R-19 when installed 50 years ago but over the years settled in to a thinner and less effective layer. The new insulation will meet our state’s code requirement of R-49 minimum and should reduce the energy required to heat the home. As I write this, the outside temperature is 12 degrees F/-11 deg C.

Is Burning Wood Carbon Neutral?

The EPA and the European Union rate wood as “carbon neutral” – although whether it is or not “depends”. When a tree grows, it takes carbon out of the atmosphere. When the tree is cut down and burned (or decomposes), it releases that carbon back into the atmosphere. However, when new trees are planted to replace that tree, the cycle repeats, with new trees removing carbon from the atmosphere. Hence, over time, wood is seen as a renewable, carbon neutral source of heating.

Whether it is carbon neutral “depends” on various factors. The EU reportedly imports up to half of its wood pellets from American forests, where wood is processed into pellets and then shipped across the Atlantic. Another critique is about which trees are cut. Older large trees remove more CO2 than young, small trees. Replanted trees can take years until they are consuming significant amounts of CO2.

Some pellet producers use scrap such as saw mill waste and blown down branches or trimmed parts of trees to make pellets, thereby avoiding cutting down trees specifically for wood pellets.

Our home is heated with a wood pellet stove. The wood pellets are manufactured by a local company that uses saw mill scrap and forestry management scrap (cut or blown down branches, small trees) for its raw material input.

Drawbacks of wood pellet heating include having to move 40-pound pellet bags around, our home is often 50-55 degrees in the morning and it takes a bit of time to warm up. I spend the morning wearing a stocking cap and heavy sweatshirt or a jacket.

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1 Response

  1. November 28, 2019

    […] people believe EVs are zero emission vehicles. As explained here, they are not zero emission when considering their lifetime energy use. In many instances, EVs […]

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