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We're already well in to 2025 and I've not yet got around to performing my annual carbon audit. This will be my sixth year, and even though the numbers are always closer to the approximate end of the scale, that means it's got to the stage where it's possible to start identifying trends.

Here's all of the data I've accumulated so far, including my carbon footprint for 2024 (i.e. the year to now). This data covers both Joanna and me, so for two people. It's not exactly household data because between 2019 and 2022 we were actually working in different countries, so were technically two households. But since then we've both been living under one roof again.
 

Source (CO2 tonnes)	2019	2020	2021	2022	2023	2024
Electricity	0.50	0.40	0.59	1.14	1.66	1.37
Natural gas	1.18	1.26	1.66	0.81	-0.25	0.02
Flights	5.76	2.26	1.90	5.34	1.32	0.00
Car	1.45	0.39	0.39	1.01	1.00	1.12
Bus	0.00	0.01	0.02	0.01	0.31	0.22
National rail	0.08	0.01	0.02	0.00	0.70	0.47
International rail	0.02	0.01	0.00	0.04	0.01	0.01
Coach	0.00	0.00	0.00	0.00	0.00	0.03
Taxi	0.01	0.01	0.01	0.01	0.01	0.01
Food and drink	1.69	1.11	1.05	1.35	1.07	1.07
Pharmaceuticals	0.26	0.32	0.31	0.06	0.13	0.13
Clothing	0.03	0.06	0.06	0.12	0.23	0.23
Paper-based products	0.34	0.15	0.14	0.37	0.38	0.38
Computer usage	1.30	1.48	0.75	0.93	0.23	0.23
Electrical	0.12	0.29	0.19	0.03	0.01	0.03
Non-fuel car	0.00	0.10	0.00	0.12	0.92	0.92
Manufactured goods	0.50	0.03	0.03	0.05	0.11	0.11
Hotels, restaurants	0.51	0.16	0.15	0.10	1.21	1.21
Telecoms	0.15	0.05	0.04	0.03	0.05	0.05
Finance	0.24	0.24	0.22	0.04	0.02	0.00
Insurance	0.19	0.11	0.10	0.04	0.04	0.04
Education	0.05	0.00	0.04	0.01	0.00	0.00
Recreation	0.09	0.06	0.05	0.03	0.06	0.06
Total	14.47	8.50	7.73	11.65	9.25	7.73

What can we say about these numbers? The headline result is that this year is joint-lowest on record at 7.73 tonnes of CO₂. Lower is better, so this is a result I'm happy about. The other similarly low year was 2021, but that was slap bang in the middle of the pandemic, so rather a special case.

This year has been a relatively "normal" year, for some understanding of normal. If you account for the pandemic, I'd argue there's a good trend in the numbers: a decline from the high of 14.47 tonnes of CO₂ in 2019 to nearly half that amount this year.

To understand why, it helps to look at the numbers that have gone in to the calculation.
 

Source	2019	2020	2021	2022	2023	2024
Electricity	1 794 kWh	1 427 kWh	3 009 kWh	4 101 kWh	5 975 kWh	4 947 kWh
Natural gas	6 433 kWh	6 869 kWh	9 089 kWh	4 439 kWh	-1 362 kWh	136 kWh
Flights	36 580 km 20 flights	14 632 km 8 flights	25 542 km 14 flights	36 042 km 20 flights	7 233 km 4 flights	0 km 0 flights
Car	11 910 km	2 000 km	3 219 km	8 458 km	8 369 km	9 364 km
Bus	1 930 km	40 km	168 km	133 km	3 080 km	2 065 km
National rail	5 630 km	400 km	676 km	0 km	19 638 km	13 184 km
International rail	64 km	1 368 km	513 km	8 684 km	2 322 km	1 914 km
Coach	0 km	0 km	0 km	0 km	0 km	1 200 km
Taxi	64 km	37 km	100 km	100 km	100 km	100 km
Tube	0 km	0 km	0 km	0 km	100 km	100 km

As you can see, the biggest behavioural change has been a reduction in flying. This is partly — but not entirely — due to a change in circumstances. While living in Finland I was never able to find a practical alternative to flying between there and the UK (the shortest ferry and train alternative was a three-day trip). Now I'm in the UK I'm no longer making this regular journey. On top of that one of my 2024 new year's resolutions was to make twelve ecological improvements to my life. Avoiding flights was one of those and thankfully Joanna has been incredibly supportive in making this happen.

Despite this restrictions we did get to travel on holiday in 2024, but strictly by train and ferry. Avoiding flights did also impact my work plans and I'm grateful to my colleagues for also being supportive. I'm glad I was able to stick to this and the results are, I think, clear.

That's not the only story in these numbers. You can also now start to see the impact that switching from gas central heating to an air-source heat pump in 2022 has made. Natural gas usage has dropped right down (we still have a gas cooker, but I'm hoping to change that). The combined power usage, measured in kWh, is substantially lower after the change, giving an indication of the improved efficiency.

As a side note, it may seem odd that gas usage in 2023 was negative. That's due to our energy company not predicting the change caused by the heat pump and having to give us a rebate on anticipated gas usage. It's not ideal for the numbers, but I couldn't think of a better way to deal with it.

Another thing that's become clear is how much impact the pandemic had on our energy use. The four flights I took in 2021 were completely offset by other carbon outputs when compared to last year, when I took no flights at all. The pandemic really did hit the world hard.

As always I've used these numbers to offset my carbon output for last year, using the UN Framework Convention on Climate Change to support cooking stoves in Malawi. To be honest, I don't know whether this really makes a real difference to my climate impact, but it feels like a good cause either way.

More importantly, it's becoming clear that these annual audits have genuinely affected my behaviour, which in the longer term, may be the bigger win.

To generate the carbon output numbers above I used Carbon Footprint Ltd's carbon calculator. According to the same site, the average worldwide carbon footprint per person is about 4.79 tonnes. Taking into account the fact Joanna and I are two people, that now puts us below the average for the first time. It's a pretty clear conclusion, at least for our lifestyles: to really make a big difference, stop taking the plane.
 
 

The old year is now old and the new year is still — relatively — new. Which means it's time for me to look back at my old year's resolutions from 2024, review them, admit my failings and then, as if lacking any form of self-awareness, make resolutions that I think I might keep in 2025.

This being the fifth instalment you know the drill and I'll try to keep things brief. So let's get straight to my list from 2024.
   

1. Start working through "Information Theory: A Tutorial Introduction" by James V. Stone.
2. Do something practical in Rust.
3. Make twelve incremental ecological improvements to my life.
4. Go to at least three events or exhibitions at the British Library.

Starting from the top, I'm happy and a little astonished to say that I did start working through James Stone's introduction to Information Theory. Working together with a couple of friends, we got through to Section 2.3. The book has nine chapters in total so that really is only just the start. But at least it is a start.

Second we have my resolution to do something practical in Rust. I've continued attending and following the Rust reading group at work, but I admit that I've yet to find a practical outlet for the skills I've been learning. This falls entirely down to lack of motivation. If I really wanted to I could have found something, but the fact is it's much easier to work in a language I'm already proficient in. I don't plan to move it to my 2025 resolutions — there's no point in forcing it — but I'll keep it as a general goal. Doing this would offer real personal benefit.

Third is my desire to make twelve incremental ecological improvements to my life. The idea was to try to find roughly one per month. In practice and, somewhat to my surprise, I came within touching distance of achieving this. Many of the improvements were small, but that was the point: continual small improvements that could accumulate to become bigger aggregate improvements over time. I tried to keep track through the year:

1. I planted our family Christmas tree from last year and miraculously it's still apparently healthy in the garden twelve months on.
2. Joanna and I looked seriously into buying a new car, but decided that it would be better to keep our existing, 15 year old, car instead.
3. I avoided using the dishwasher for 12 months. I've replaced it with washing up by hand, being careful to keep water usage low enough to be more efficient than the dishwasher would be.
4. When I take a shower I now intentionally reduce the heat. Previously I always showered with the maximum, now I reduce it by quarter of a turn. It's a small win, but has the potential to be improved on in 2025 with an extra turn of the tap.
5. At the recommendation of a friend at work I'm now buying only certified shade grown coffee. Apparently this is much better for the environment.
6. This year I made special effort never to travel by plane. Given my previous years' failings I have plenty to make up for here. But I succeeded in making zero flights this year.
7. When choosing my new home server, low power usage was a primary requirement. The device I ended up with is fanless and averages around just 12 Watts.
8. I've also made a special effort to travel by train. Joanna will attest to this, as she's been very supportive when travelling together.
9. Between June and August I cycled to Cambridge and back for my work commute seven times out of a possible 13. So there's room for improvement, but still better than the five I managed in 2023.
10. Last January I offset my carbon output from 2023 with 10 Certified Emission Reductions.

As you can see, that's actually only 10 items. On top of this Joanna and I also made active moves to get solar panels installed and to switch our hob from gas to induction. These are still works-in-progress, but are also longer-term goals. So I think I can only claim this one as a partial success. On the positive side, I'm convinced it was only my commitment to this resolution that made me do some of these things, which makes me feel this process is worthwhile, even if I don't always succeed.

Finally, I committed to going to at least three events at the British Library. In this I succeeded, visiting the Fantasy: Realms of Imagination, Beyond the Baseline: 500 Years of Black British Music and Medieval Women: In Their Own Words exhibitions. Honestly, all three were fantastic; better even than I'd expected. So I'm glad I committed to this.

In total then for 2024 it's 2.83 out of four: a pretty good result in my world. So what's in store for 2025?
 
Here are my planned resolutions for the year ahead:

1. Prioritise Codeberg over GitHub.
2. Do something fun outside the house at least once per week.
3. Read at least one paper per week.

I've kept these descriptions brief so let me break them down a bit. I've never been a huge fan of GitHub. In its early years it was clean, focused and welcoming to open source projects even if it wasn't open source itself. More recently it's become bloated and messy. More seriously it's approach to AI data collection has become — in my opinion — actively hostile to open source.

Given all this, I'd love to move off GitHub for my personal projects. The obvious alternative right now seems to be Codeberg given its strong open-source and community credentials. So I'd really like to resolve to move all my projects there. Unfortunately moving existing projects to a different platform can be destructive (for example with loss of issues and open pull requests). I'm therefore resolving to start all new open source projects on either Codeberg or my self-hosted git server. I should also start moving existing projects, but that'll have to be on a best-effort basis.

Next up I'm resolving to do something recreational outside the house at least once per week. This might sound strange to a normal person, but I spend so much time inside and online that I can easily go an entire week without doing something recreational in the real world. Of course, I often leave the house for work, shopping or other non-recreational activities. But the plan here is to do something fun. It could be going to the cinema, visiting friends or just going for a walk in the local countryside. But it should be something. I've run this past Joanna and she's on board with this: it'll be a combined effort.

Finally I plan to read at last one research paper each week. This is an idea I stole from Dr Esther Plomp, a researcher I know through her contributions to The Turing Way. Dr Plomp committed to reading one paper a day but I've diluted this to one per week to suit my own lower standards. I'm also keeping my definition of a "research paper" pretty loose. If I end up reading a book chapter instead, that's fine.

So those are my three resolutions. I thought about including several others, but I think it's important to stay focused. Here are a few that didn't make the cut:

1. Complete "Information Theory: A Tutorial Introduction" by James V. Stone.
2. Complete all the exercises in Linear Algebra Done Right by Sheldon Axler.
3. Add Cambridge live bus info to an app.

I dropped these either because I expect I'll do them anyway, or because I suspect I have no chance. I'll leave it to you to decide which is which.

With my home server back up and running I feel in good shape for the year to come. So, roll on 2025! See you in twelve months with the results in Part VI.