I was thinking about the emissions tradeoffs of various EV buying/upgrading options and came across
‘s excellent breakdown of car emissions making the case that an EV really is, generally, a lower-emissions option than even an efficient hybrid car, despite its higher manufacturing cost. I found a different framing more helpful for thinking about our particular tradeoffs and our overall transportation footprint, so I wanted to write that down here in case it’s useful to others.Ritchie starts from some default lifecycle assumptions, namely that people drive a “medium” amount per year (10-12K miles) and keep their cars a “longish” time (5+ years certainly and often 10+ years), and that people generally have home electricity which is only partly decarbonized. With these assumptions, she’s quite convincing that a compact EV is much better over its lifecycle than a compact car, even when you take into account the extra carbon required to make the battery. But different people drive different sizes of cars for different times, and the “grams emitted per mile driven” framework that she and many other sources use doesn’t make it easy to adjust for that.
So here are some round numbers I calculated based on the sources she points to and other carbon footprint calculators found online:
Manufacturing an ordinary gasoline car, either a compact sedan/hatchback or small SUV, emits 5-10 tons of CO2e. This mostly scales with the size of the car, since it’s mostly from making the steel that goes into the car’s body. Thus larger SUVs will require more emissions to produce, perhaps up to 20-30 tons.
Making an EV incurs a similar, size-dependent cost for its body plus additional emissions over and above this for the battery, to the tune of roughly 1 ton per 10 kWh of battery capacity. So EVs with smaller batteries— whether because they’re lower-range or more efficient— incur less of an initial “carbon debt”.
Burning gasoline emits roughly 1 ton per 100 gallons. This is a figure to which you can compare the emissions produced per kWh to charge an EV battery, which varies enormously depending on your electricity mix. Of course, you also need the mpg of the gas car for this comparison. You need the miles per kWh of the EV too, unless you can guarantee carbon-free electricity to charge it with, in which case you’re multiplying that mpkWh by zero regardless.
To put this in overall transportation footprint perspective, 1 ton of CO2e is about the emissions from 1 person flying cross-country one way (e.g. SFO to JFK) in premium economy.
And for comparative household perspective, 1 ton of CO2e is also about the emissions from 170 therms of natural gas: a little less than we currently use per year for the gas range, water heater, and dryer.
Equipped with these round numbers, you can look at your current lifestyle and do the math on your resultant footprint, and compare possible vehicular changes and strategies. As a worked example, our family’s current trips break down like this:
Car trips in and around the Bay Area. For these our VW e-Golf is more than adequate both space- and range-wise, so we use it almost exclusively. We’re lucky enough to do remote-friendly work so we rarely need the car for commuting.
Several ski trips to Tahoe each winter. For these we rent gas-powered SUVs, because (as I discussed earlier) going to Tahoe in winter is basically pessimal for EV range, and you really don’t want to get stuck on a snowy mountainside in a car that’s run out of charge. Also, the little e-Golf is a bit too small for all our ski equipment and does not have AWD for the snow.
Summer road trips around California. We have found that the e-Golf usually works for these with some charging-stop planning and careful packing, sometimes including hitch racks and/or roof bags. The exceptions are when we go to places like Yosemite or Lassen where chargers are still few and far between, and for these we end up renting a gas car— but that’s typically no more than once per summer.
Trips where we fly somewhere and either take transit there or rent a car there.
Since we typically take at least a couple of family airplane trips a year, and each round trip accounts for 3-6 tons of CO2e, the vast majority of our transportation footprint is from those flights. Driving in case (1) is basically zero-emissions because we charge with 100% renewable power at home. Cases (2) through (4), estimating generously, amount to about 150 gallons of gas burned per year total, so 1.5 tons of CO2e, plus whatever partial imputed manufacturing debt we incur by using the rental cars.
So what are some plausible options to reduce our footprint? There’s not much we can do about the flights, unless we just forgo trips that we really value, or spend multiple irreplaceable extra days per trip getting there and back. One can buy offsets, and indeed we do, but the “additionality” of most of these is dubious— and perhaps worth examining in a separate post. Longer term, it’s worth watching how airlines’ actions on this evolve, to see if we can reward those that move toward systemically lower emissions first, e.g. by scaling up the use of renewable fuels.
What if we bought a new, longer-range EV usable for road trips, i.e. for driving in cases (2) and (3)? That would incur an initial carbon debt of somewhere between 12 and 20 tons, assuming that we would need a 70-100 kWh battery to have roadtrip-capable range. By comparison, the cars we rent typically get at least 30 mpg on the highway. So even at the low end of the initial debt estimate, and even if all the recharging came from renewable energy, we’d have to do 36,000 miles worth of road trips to pay it back— which is at least 10-12 years worth at our current pace. More realistic assumptions could put the payback period at 15+ years, and it’s hard to even know how much we’ll be driving around that far in the future, when our circumstances might be quite different.
Another option would be to do more work to find rental EVs for our roadtrips, as we did over Christmas. There are a few emerging ways to do this, including traditional rentals and “peer to peer” services like Turo. Right now these are very spottily available, inconvenient, expensive, or all of the above, but we’ll keep checking to see if and how that changes.
Of course, CO2 emissions reduction is not the only goal of purchase decisions. For example, we may decide we want a roadtrip EV anyway, because it’s so much nicer to drive, or because it reduces emissions of other harmful pollutants besides CO2. But at least this way we can be clear about what our choices actually will and won’t achieve.
Note too how sensitive all this is to each household’s particular circumstances. If we had a larger family, or did longer road trips, or went to Tahoe every single weekend all winter, or needed two cars for long commutes to two jobs, or lived someplace with worse charging infrastructure or dirtier electricity than California, all these numbers could work out quite differently. That’s the idea behind giving you the figures up top: plug them into your own lifestyle and see what comes out! And if you have sources that dispute any of the numbers I’ve listed, please let me know.