Epistemic status of this post: I am not an expert, but I am reading people who are. There is every chance that I have messed up somewhere so if you know about this area I welcome correction, but in the absence of that the numbers seem relatively robust.

General disclaimer: This is UK centric. The general theme and advice is probably quite portable, but the specific numbers will vary quite a lot depending on who and where you are.

Due to a combination of long-running family arguments and the fact that now that I’m earning money again I’m planning to invest a lot of my earnings in charitable giving, I’ve been looking into various ecological statistics and costs and I’ve come to the following conclusion:

1. Based on typical UK lifestyles, it is very hard for any personal ecological intervention to be more cost effective at reducing carbon emissions than giving money to an effective climate change charity.
2. The amount of money you need to spend to go carbon negative is surprisingly small.

Here are my calculations. Note: I am deliberately rounding things up on the grounds that these are ballpark figures.

Based on the UK greenhouse gas emissions national statistics from the government, the UK is currently emitting the 568.3 million tonnes per year of CO2 equivalent greenhouse gasses (467.5 million tonnes of CO2, the rest is other greenhouse gasses).

Based on this report from the committee on climate change, this is artificially low due to CO2 imports from countries that do manufacturing for us, and the real CO2 emissions are probably something like 80% higher than that. This comes to 841.5 million tonnes of CO2 equivalent.

The current population of the UK is 64.1 million. So dividing 841.5 by 64.1 (the millions cancel), you get about 13.1 tonnes of CO2 per year per person.

Note: This includes a whole bunch of industrial usage that you have no direct control of. e.g. if everyone in the UK became vegan overnight (which according to this Guardian article can save up to about 1.5 tonnes per year if you’re starting from a meat rich diet), all the cattle and other agricultural animals aren’t going to evaporate, we’re just going to export more. You will reduce demand, and thus production, but you’re probably not able to reduce your “share” of the production to zero. So this is already an overestimate of how much greenhouse emissions we can actually exert a direct influence over.

Now, lets arbitrarily double and round up on the grounds that you might be a high carbon footprint person if you’re eating more meat than average, driving everywhere, etc. We’re trying to create a comfortable overestimate of how much you could reduce your carbon footprint. Your mileage may vary.

So lets say for the sake of the argument that you personally have a carbon footprint of up to 30 metric tonnes of CO2 equivalent.

How much would it cost for you to offset this?

Note: Although I have some doubts about the efficacy of any given choice of carbon offsetting, atmospheric carbon is the ultimate fungible resource. Distribution matters a bit, but ultimately the amount of CO2 in the atmosphere is what matters the most, so I think thinking in terms of offsetting here is completely valid.

Anyway, cost. There seem to be a variety of reports.

1. This guardian article (note: from 2011) claims that £8 / tonne is “typical”. That would make this a price of £240 / year.
2. The fixed offset calculator from the world land trust claims that we should be paying them £450 / year to offset 30 tonnes of carbon
3. This analysis from Giving What We Can claims that Cool Earth are extremely effective to the tune of saving one tonne of carbon per £0.85 donated. That would make a £25.5 / year donation to them effective at offsetting these 30 tonnes!

Obviously this is quite a range. However, even the upper bound of £450 is just not that large (for poorer people and families obviously it’s much more significant, but note that within the UK at least poorer people are also likely to have smaller carbon footprints. I do not know how much of this is mediated by the fact that poorer people are disproportionately likely to be urban). Especially when you consider that this is a significant overestimate of how much you are likely to need to offset.

What this means in practice is:

1. If the analysis of their effectiveness is at all believable (I have a reasonable amount of non-expert confidence in it, but I have not done a close reading of the report), a recurring donation of £10 / month to Cool Earth is probably enough to make you significantly carbon negative. Even if it is an order of magnitude too optimistic, £20-30 / month should still be enough to make you carbon neutral unless your lifestyle is truly exorbitant for the UK.
2. If a personal intervention costs you something you value as much as £10 pounds per month it’s probably not worth it and you might want to consider offsetting instead.
3. Even if you want to reduce your personal ecological footprint, you should strongly consider giving money to a charity such as Cool Earth, because it lets you make your net ecological footprint go negative.

This suggests the following rules of thumb:

1. If a personal intervention net costs you money, it’s probably not worth it. Give the money to Cool Earth instead.
2. If an intervention requires a regularly (say as often as once a month) recurring action that each time you perform it you would rather give £1 to Cool Earth, you should consider not bothering and giving a bit more recurring money to Cool Earth instead.
3. If you have particular habits that have a high carbon cost per instance (e.g. long distance travel), consider offsetting them with a donation each time.

2 requires a little unpacking. It would of course be better to do both. However, my thesis is that you are more likely to stop doing annoying actions than you are to stop recurring donations: One requires active intervention to keep doing, the other requires active intervention to stop. Moreover, we tend to have a “virtue budget” where because we feel good about ourselves for doing one thing we’re likely to do less of another (I have seen Science on this but do not currently have a cite, so take this information well salted). So given the relatively low effectiveness of doing things which will annoy you, the high chance of stopping them, and the comparative effectiveness of less annoying alternatives, it’s probably better to just go with the less annoying alternatives.

Personal interventions that are probably worth it:

1. Loft insulation if you are living in a house you own and do not currently have it. This will save you money as well as reducing your carbon footprint. Therefore the cost is negative and thus always going to be better.
2. Replacing light bulbs with LED ones as and when they break: Saves you money, costs you no time and reduces your carbon footprint.
3. Other cost saving ecological measures for your home are probably worth it too. I’m not super familiar with this area because London living means hardly anyone I know outside of my parents own a home. There’s probably something interesting to say about the ecological costs of renting here.
4. If you can take public transport instead of driving you probably should, but this is not a practical intervention for many people because whether you take public transport tends to be more a function of where you live than an easily changeable aspect of your llife.
5. If your diet is high meat then eating more vegetarian meals is probably a good thing anyway and will save you money without costing you time, but bear in mind that you could eat meat every day and chuck £10 to Cool Earth at the end of the year and still save more carbon than by going vegan, so this is probably not a valid reason to go vegetarian.

Addendum and other considerations

1. There is more to saving the planet than CO2 emissions, but it’s a pretty good start. However, other considerations may affect the validity of some interventions. For example although you save comparatively very little CO2 by going vegan, you do probably save upwards of 1000 litres of water per day, and water is significantly less fungible than CO2 because of the difficulty of transporting it. So decreasing your meat consumption may be a valid intervention after all, or you might want to just chuck another £10 / year at some charity building desalination plants, I don’t know. More research needed.
2. Even if the estimates of their effectiveness at CO2 offsetting are wildly overstated, Cool Earth’s approach helps poor communities and preserves biodiversity, and thus seem like a worthwhile charity strictly on those grounds. However if they were contributing literally zero carbon offsetting benefit, Giving What We Can’s DALY comparison against the Against Malaria Foundation (who I have currently let my donation to lapse, but will be resuming it once I’ve sorted out my finances) makes Cool Earth the less compelling alternative of the two.
3. With any charity, there is a point of diminishing returns. Cool Earth do not appear to be at that point yet according to the Giving What We Can analysis (which is a few years old, but showed sufficient headroom that they are probably still going strong). It is very unlikely that we can achieve the needed global carbon reductions purely through direct offsetting. I have no idea if Cool Earth could productively use £640 milion per month (everyone in the UK giving them £10 / month), but I doubt it. However we are currently so far from that point that I think it is not a major concern.
4. Medium and long-term, we still need systemic change. Short-term, we have the emissions equivalent of a Wonga loan and almost nothing matters except for paying it off. In order to balance these two it is probably worth diversifying your charitable giving and giving some of it to advocacy groups. More research needed one effectiveness here (the linked Giving What We Can piece has some analysis here. It’s a few years old though and the analysis of effective advocacy probably changes faster than effective climate change interventions).