November 6, 2019

I am a dad, so, in accordance with ancient tradition, I spend much of my day going around the house switching lights off to save energy. Similarly, I like to tell my wife and children that it’s “like a sauna in here” and demand that we turn down the heating. Roughly speaking, I think of those two dad-rituals as equivalent. They’re both “saving energy”, and are therefore Good Things.

But are they really? We’re not very good at thinking about scale, as a species. To put it in perspective, you can run a modern LED bulb for about 120 hours per kilowatt-hour (kWh) of electricity. The growth of renewables and decline of coal means that those kilowatt-hours are less carbon-intensive than they used to be, which means the generation of each kWh produces about 200g of carbon dioxide equivalent (CO2e).

This means that leaving the lights on creates between one and two grammes of CO2e an hour. The first boiler I found online had an output of 12KW, so one hour of running that boiler is the equivalent of 1,440 hours of leaving a light on — or, if you prefer, running your boiler for about three seconds is the equivalent of leaving a light on for an hour.

Why am I musing on my role as household saver of trace quantities of CO2?  Because of a story last week about asthma inhalers and carbon footprint, which the BBC reported as “Asthma carbon footprint ‘as big as eating meat’”.

I think it’s a bit misleading — besides which, the presentation makes it seem somehow asthma sufferers’ fault. But I also think it’s instructive of how we think about scale, and this goes beyond the arguments about climate change.

Here are the numbers: there were 50 million inhalers prescribed in the UK in 2017; about 35 million of those use propellant gases called hydrofluoroalkanes, or HFAs. HFAs are favoured because CFCs were banned for the whole destroying-the-ozone-layer thing, but they’re enormously potent greenhouse gases. Several hundred or several thousand times as powerful, by weight, as carbon dioxide.

The BBC, quoting research by Cambridge University, says that replacing “even one in every 10 of these inhalers” with a different kind would reduce greenhouse gas emissions by the equivalent of 58 kilotonnes of carbon dioxide, or “the carbon footprint of 180,000 return car journeys from London to Edinburgh”.

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Even more dramatically, “at the individual level, each metered-dose inhaler replaced by a dry powder inhaler could save the equivalent of between 150kg and 400kg (63 stone) of carbon dioxide a year”. That is, they say, about the equivalent of the saving you’d make by quitting eating meat.

(Before we go any further, I want to quibble a bit with these numbers. The BBC lifted that last paragraph almost verbatim from a Cambridge press release; the original phrasing was “At the individual level each metered-dose inhaler replaced by a dry powder inhaler could save the equivalent of between 150 and 400kg of CO2 annually”. I don’t know about you, but I definitely read both of them as saying that each inhaler produces that.)

But 58 kilotonnes is 58 million kilogrammes. Divide 58 million kilogrammes by 3.5 million inhalers and you get about 16kg per inhaler, ie about 10% of the lowest estimate. GlaxoSmithKline reckons that each of its HFA inhalers creates the equivalent of 18kg of carbon dioxide, so that’s probably the right ballpark.

(I asked Cambridge and they said, yes, they were assuming that patients use about 12 of them a year. I think that’s a bit misleading and that the BBC, and Cambridge, really ought to clarify it. Still, though, that headline figure of 58 kilotonnes is probably about right.)

So it’s basically right, but is it a lot? Fifty-eight thousand tonnes of carbon dioxide sounds big, but everything sounds big. Well, I had a go at looking at some other things. For instance, since I mentioned it before, how about heating your house? The 23 million or so households in the UK use a total of about 350 terawatt-hours (TWh) of energy a year, depending on how cold the winter is.

One TWh is one billion kWh, so as we saw earlier it produces on average about 200,000 tonnes of carbon dioxide equivalent (CO2e). So heating British homes creates about 70,000,000 tonnes of CO2e — 1,200 times greater than 58 kilotonnes.

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Or how about eating meat, since that’s the example the BBC gave. The average Briton eats about 85kg of meat a year, according to Our World in Data. Let’s assume that’s half-beef and half-chicken, which is a silly assumption but probably won’t lead us too far astray. According to the University of Michigan Centre for Sustainable Systems, a kilo of beef creates about 15kg of CO2e and a kilo of poultry about 3kg, so that’s an average of 9kg. Nine times 85, multiplied by a UK population of 66 million, gives us about 50 billion kilos of CO2e a year, or about 900 times bigger than 58 kilotonnes.

Even if we start talking about replacing all of the HFA-propelled inhalers, rather than just one in 10 of them, the impact of asthma on British carbon emissions is probably on the order of 1% of that of heating our homes or eating meat.

This story is an interesting one if you’re, say, a doctor of respiratory medicine, who might think it’s a good reason to prefer prescribing dry powder inhalers rather than HFA ones, all else being equal. But it’s of almost zero interest to the general public, and will just mean that asthma sufferers get told “don’t you know that’s bad for the environment?” all the time by the sort of person who only reads headlines.

But we aren’t very good at thinking about scales and proportions. In general, I think, we assign things a value of ‘good’ or ‘bad’, and bracket them all together in those two categories. For instance, we feel good when we take a bag-for-life to reduce plastic bag use. But you can make 1,000 bags for 6kWh, while boiling a kettle takes about 0.1kWh, so you could make 16 plastic bags for the energy cost of just one round of tea.

From a purely climate point of view, your plastic bags are largely irrelevant. Reducing plastic waste is also good, of course, although again, Western countries account for a tiny fraction of the ocean pollution we worry about — almost all of it comes from Asia and sub-Saharan Africa, in fact.

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It’s not just environmental things. We do it with money, too. I worry about whether or not to give Apple an extra £1.28 a month to increase my iCloud storage, which is ridiculous compared to the unprintable sums I haemorrhage on rent.

At the national level, I saw David Schneider, the comedian, tweeting something about how the Tories were the party of “£100m on Brexit ads, £11m on Brexit 50ps, £8bn on No Deal prep, £13.8m to ferry company with no ships, £600m a week in lost investment/growth”, as though these things were equivalent. But even if those numbers are right, the Brexit ads, the 50ps, and the ferry company added all together make up about 1.6% of the No Deal prep. It’s bizarre to include the decimal place in “£13.8 million” when £13.8 million is itself a rounding error when compared to £8 billion.

None of this is meant to make you stop taking care over the small things: look after the pennies and the pounds will look after themselves, as they say. There’s nothing wrong with stopping using plastic bags, although you need to be very careful that you don’t lose your cotton bags-for-life, since they use about 100 times as much energy to make.

But we ought to pay a bit more attention to where the line is between the penny stories and the pound stories. Asthma inhalers are not a major source of British greenhouse emissions; as I say, they should be a consideration for GPs and doctors of respiratory medicine, not for the rest of us, and certainly not for worried asthma sufferers.

And we dads, as we walk from room to room complaining that it’s like “the bloody Blackpool illuminations in here”, should shout at our children much more about leaving the heating on than the lights on – about a thousand times more, in fact.