Air miles, road miles

9 November 2019

Cutting our transport footprint means cutting our transport miles - electric vehicles can only be part of the answer

Car travel and flights were 28% of our baseline carbon footprint for 2018. The table below summarises where it comes from (for our family of five) and compares 2019 with 2018. 

*Carbon footprint includes a 1.9x radiative forcing factor to reflect the increased warming effect of high-altitude emissions.

Our hybrid and small runabout both achieve around 50 mpg, which means that the car emissions aren’t as bad as they could be, but it’s still a sizeable amount. The impact of our flying habit is quite an eye-opener.

Cutting the carbon cost of flying

The table demonstrates the impact of long-haul air travel. Over the last few years we’ve typically taken one long-haul trip per year, although not always as far as California, plus a trip to Europe. We have family in Glasgow so we also tend to use a lot of short internal flights within the UK. Although the table is shocking by virtue of the sheer size of the carbon impact of flying, it also shows how changing habits can quickly make a sizeable impact on the footprint. Choosing a medium haul holiday destination this year and taking the train rather than the plane to Glasgow where possible (or driving) has enabled us to more than halve the impact of our flights. Of course these alternative forms of transport to some degree offset the saving, but the carbon cost is still a fraction of flying. 

Given the impact of flying on our footprint, there was little option but to cut the amount we fly if we want to have a chance of halving our footprint by 2025. We’ve targeted reducing to a rolling five year average of 1 Tonne per head per annum by then, around two-thirds below our baseline for the few years up to and including 2018. This will in essence mean taking a long-haul flight at most every three to four years, using the train or driving wherever possible to get to Glasgow, and more frequently choosing European holiday destinations that we can get to by car or train (next year we’re driving to Provence). 

It's encouraging that this year we've already made substantial progress towards meeting this goal. Moreover, this is an area where the costs in terms of lifestyle can be overstated. Living in Europe, there are many great destinations that fall within a train journey or drive. And if we choose not to go long-haul too often we can fly to the Canaries, Madeira, North Africa, Turkey or Russia every year within our budget. This is not excessive sacrifice. Of course you could argue that we shouldn’t fly at all. And maybe it will come to that. But our commitment is to halve our footprint by 2025, not cut it to zero. In terms of flights I think this will be possible with very little drop in utility.

Given the difficulty of finding technological solutions to the carbon intensity of air travel in the near future, this is likely to remain one of the most problematic aspects of western carbon footprints, especially for the better off. There are, of course, difficult second order issues here too. Many local economies around the world are now built on tourism that is fed by cheap air travel. Cutting that travel may help with carbon impacts for the long term but will have immediate short term negative economic impacts. This is another reason for gradually cutting, rather than axing, air miles, with a focus on substitution for other forms of transport where possible (e.g. using train or car instead of domestic or short-haul flights). 

Greening our road miles

Most analysis now clearly shows that electric vehicles (EVs) have about half the lifetime carbon emissions of a typical petrol vehicle, and well below even an efficient hybrid. This is particularly true in the UK where the carbon content of electricity is falling quite quickly (see here for a good summary). Although there are some environmental and human rights concerns relating to the extraction of rare earths for battery usage, it now seems pretty clear that wider adoption of EVs will likely play a major role in the move to a low carbon future (although wider use of hydrogen, manufactured using renewable energy, should not be ignored as a possibility). A network of battery powered cars also create the opportunity for dynamic grid management with the country’s fleet of electric vehicles acting as a huge battery farm to enable balancing of supply and demand in the grid, mopping up renewably capacity when it’s plentiful and releasing it back into the grid when not. 

So choosing an electric vehicle makes sense when buying a new car. But what about trading in before the end of a car’s life? We’ve been considering trading in our Yaris (our second car) for a small EV. I estimate that around 80% of our car miles are less than 50 miles a day, comfortably within the range of a small modern lightweight EV. This would leave our hybrid available for longer journeys, which can still be more awkward for EVs given mixed availability of charging facilities. As I count our electricity supply as being essentially carbon free I'd earmarked a reduction in over 2 Tonnes pa from our carbon footprint through acquiring an EV. 

But then I thought about what happens to the Yaris when we sell it. If it simply replaces a less efficient car on the roads, without increasing the overall stock of cars, then trading it in would make sense. If the least efficient car on the roads is scrapped when we buy by our EV and sell our Yaris then the overall carbon efficiency of the UK car stock has gone up. 

Unfortunately it doesn’t work like that. The DVLA publishes information on new car sales, total car stock, and total miles driven. The chart below compares new car sales with the total number of cars on the road over the last 20 years (units are in 000s of cars):

There is an extremely strong correlation, showing that new car sales drive up the total stock of cars rather than simply affecting its composition. The trend-line shows that typically each four new cars purchased result in three additional cars on the road – only one is taken out of circulation. Further analysis on mileage shows that more cars on the road lead to more miles driven (unsurprisingly!). Each new car registered is associated with a further 6,800 miles driven. The old vehicles cascade their way down the chain, and become a first-time second (or third) car for someone else, leading to incremental miles driven.  So the reality is that buying an EV and selling our Yaris results in a net increases in the stock of cars and miles driven. Only 0.25 of a car is taken out of circulation, and our Yaris becomes a second car for someone else adding 6,800 miles driven. Furthermore, we have to account for the carbon content of our new EV.

So how do I think about our upgrade now? The rough calculus is set out below.

The overall conclusion is that the significant annual carbon saving from running an EV rather than a petrol car is offset by the carbon cost of the car plus the likely additional miles driven due to adding a further car onto the road. My estimates suggest that this is broadly a carbon neutral decision, and could even be carbon negative to make the change, depending on your view of the carbon cost of electricity. For example, it is sometimes argued that incremental electricity demand is likely to be met in the short term by burning more fossil fuels, and so the additional electricity to drive electric cars is likely to be more carbon intensive. Set against this, cars can be charged at times when renewables otherwise wouldn’t be used (at night, for example) and provide an important balancing mechanism. 

If the new car is being bought because an old car has come to the end of its life then the choice of EV is unambiguously favourable from a carbon point of view. The old car is scrapped and so adds no new miles. The carbon cost of a new EV is only slightly more than for a new petrol car. The saving is then genuinely 1.5 to 2.5 Tonnes pa depending on your view of the carbon cost of electricity. But if the petrol car has continued useful life it is a different matter. This illustrates the challenge of sunk capital in energy transition. Large scale write-offs of existing resources are not always the right approach even if the carbon run-rate of the replacements is lower. I was struck by the analogies with the corporate experience (read about my interview with Michael Lewis, CEO of E.ON UK, here).

Overall, my assessment is that upgrading to an EV will not provide the carbon saving I had hoped. It is overall broadly carbon neutral. However, the signalling impact is important.   Manufacturers will not invest in EV production and infrastructure, and Governments will not seek to push regulation to accelerate the change, unless they see demand from consumers. Greater use of electric vehicles by early adopters will help other purchasers overcome doubts and see their benefits. It also raises the profile of climate as a valid consideration in consumer decisions. Even if the short term carbon impact of changing to an EV is neutral in isolation, the power of signalling and example is also important. 

My conclusion is therefore to upgrade our Yaris to a lightweight small EV in which we hope to do most of our miles. We can afford to be an early adopter to support the market for an important emerging technology, which will play an important part in the fight against climate change. This might not contribute the hoped-for reduction to our carbon footprint - those savings will have to come from elsewhere - but it remains a worthwhile contribution to signalling the need for change.

Flights simple, EV complex

The analysis on flights is simple. Less is more. But for cars it’s more complex. Apparently sound approaches, like buying an EV, only unambiguously make sense when an existing petrol vehicle has come to the end of its life and is being changed in any event. Changing a relatively new petrol car is at best neutral. However, as it is probably not net negative, and is a powerful signal of change, it is still worth doing in my view.

Wherever we turn to try to reduce our footprint, second order effects are uncovered. Some of the low hanging fruit rises agonisingly out of reach as you approach it – it’s going to be harder than I thought. But not impossible. We’re just going to have to push harder for savings elsewhere.

This blog if part of a series sharing our learning and experiences as we adopt a Middle Class Approach to Decarbonisation

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