On March 30, David Mackay, author of Sustainable Energy without the Hot Air, will be giving the J Tuzo Wilson lecture in the dept of Physics (Details of the time/location here). Here’s the abstract for his talk:

How easy is it get off our fossil fuel habit? What do the fundamental limits of physics say about sustainable energy? Could a typical “developed” country live on its own renewables? The technical potential of renewables is often said to be “huge” -but we need to know how this “huge” resource compares with another  “huge”: our huge power consumption. The public discussion of energy policy needs numbers, not adjectives. In this talk I will express power consumption and sustainable production in a single set of personal, human-friendly units. Getting off fossil fuels is not going to be easy, but it is possible.

The book itself is brilliant (and freely available online). But David’s visit is even more relevant, because it will give us a chance to show him a tool our group has been developing to facilitate and share the kinds of calculations that David does so well in the book.

We started from the question of how to take “back of the envelope” calculations and make them explicitly shareable over the web. And not just shareable, but to turn them into structured objects that can be discussed, updated, linked to evidence and so on (in much the same way that wikipedia entries are). Actually, the idea started with Jono’s calculations for the carbon footprint of “paper vs. screen”. When he first showed me his results, we got into a discussion of how other people might validate his calculations, and customize them for different contexts (e.g. for different hardware setups, different parts of the world with different energy mixes, etc). He came up with a graphical layout for the calculations, and we speculated how we would apply version control to this, make it a live calculator (so that changes in the input assumptions propagate like they would in a spreadsheet), and give each node it’s own URL, so that it can be attached to discussions, sources of evidence, etc. We brainstormed a long list of other features we’d want in such a tool, and we’re now busy creating a first prototype.

What kind of tool is it? My short description is that it is a crowd-sourced carbon calculator. Because I find existing carbon calculators to be very frustrating, because I can’t play with the assumptions in the calculations. Effectively, they are closed-source.

At the time we came up with these ideas, we were also working on modeling the analysis in David Mackay’s book (JP shows some preliminary results, here and here), to see if we could come up with a way of comparing his results with other books that also attempt to layout solutions to climate change. We created a domain model (as a UML class diagram), which was big and ugly, and a strategic actor goal model (using i*), which helped to identify key stakeholders, but didn’t capture the main content of Mackay’s analysis. So we tried modeling a chapter of the book as a calculation in Jonathan’s style, and it worked remarkably well. So we realized we needed to actually build the tool. And the rest, as they say, is history. Or at least will be, once we have a demo-able prototype…


  1. “I find existing carbon calculators to be very frustrating, because I can’t play with the assumptions in the calculations.” Exactly – you’re spoonfed numbers someone else has come up with, with no idea where they came from…

  2. Dan: yep. Our long term goal is to open up the calculations so that a broad community can seek consensus both on how to make such calculations and what input assumptions are appropriate. The bigger part of this is of course, the social process around this consensus building, rather than the tool itself. We’ll probably end up adapting something like wikipedia’s editing processes, if this ever takes off…

  3. Question: how would you get from that to anything like a consistent standard for comparison? I went to a talk by Nicholas Stern last night, and a couple of questioners bought up the issue of carbon accounting. It struck home to me that there does need to be some consistent method of comparison. I’m trying to envisage a scenario where, perhaps, different approaches emerge, but wrappers exist for converting between them. Long term, would you expect some sort of consistent system to emerge?

    Stern also mentioned he was off to China, where apparently they have many models of carbon accounting and – unsurprisingly – they’re keen to emphasise the carbon responsibility inherent in the act of buying, not just producing. That’s where it gets really tricky, for me: so many options. I mean: consider that China keeps its currency set to help its exports, and underpins certain export sectors. That makes people buy more than they would. Where to put the carbon buck then?

    Sorry, this isn’t helping! I have a pathological tendency to try and complicate things.

  4. Dan: way too complicated! You cannot impose consistency. Far better to tolerate inconsistency and allow islands of consistency to emerge through a process of social dialogue. The trick is to establish just enough consistency an immediate analysis task – attempts to build a consistent map of human knowledge are doomed because human knowledge itself is messy, contingent, and often self-contradictory. (I did many years of research on dealing with inconsistency in the 90’s. Does it show?)

    So we will build simple tools for building and linking separate calculations, and explore techniques for comparing / consistency checking, etc as and when such things become salient.

  5. I know this thread is a little old but I have only just discovered this blog and this is an issue very close to my heart, so I thought I would add to it.

    Carbon accountancy calculations are not just scientific calculations. They contain ethical and political judgements which are often hidden and disguised. Attempts to impose consistency on methodology- which are well underway – are frequently attempts to impose the dominant political ideology, or the interests of those who pay for the calculations (the relevant industries generally). I find this problematic.

    Here is one example. There are now about 20 different methods of calculating the GHG emissions of biofuels, and depending on which method you use they will come out as much better, or much worse than fossil fuels. The key argument is over the idea of ‘indirect land use change’. This is land use change that happens like this: I used to grow food, I switch to growing biofuel on my land, somewhere else someone hacks down a forest to replace the food I used to grow.

    One method of calculating the GHG emissions of biofuels (to my knowledge it was invented by a consultancy called ‘Ecometrica’) goes like this: take all the emissions from land use change happening in the world and divide it up amongst products on the basis of how much land that they use. If you do this, you end up allocating a lot of the responsibility of land use change to food, and less to biofuels, so biofuels end up looking pretty good.

    But deciding on this methodology is not a technical judgement! It is an ethical one, because what you are really allocating is ethical responsibility. (Not causal responsibility- this method makes no attempt to asses causal relationships, which would require economic modelling). It contains the hidden ethical assumption that growing subsistence food is morally equivalent to growing bioenergy, and hence that they should both be allocated the same share of responsibility for any land use that occurs in the general pursuit of agriculture.

    In other words, it assigns responsibility to the poor for the sins of the rich, and also removes our ability to reduce GHGs (we can stop using bioenergy- we can’t stop eating). In my eyes, this is a disgraceful methodology.

    This post is getting rather long so I should stop, but my point is not just about this one methodology. ANY methodology in this instance is going to contain ethical and political judgements, because the question is an ethical and political one as well as a technical one. Carbon acountancy goes to the heart of society, and the questions of society are not just technical (despite what the neoclassical economists would have us believe).

    A socialist carbon calculator would be very different from a Keynsian one, which would be very different from a neoliberal one!

  6. Josie – Many thanks for this – it’s a vitally important issue. I’m gonna have to think a bit on how we handle it.

    One of our inspirations is the social process that wikipedia uses for contentious entries. We could try some variant of their “Neutral point of view” rule, in that we could set up the expectation that the different approaches to calculating these things must be represented, with commentary on the comparisons. We’re already looking at technical features that allow multiple ways of deriving a particular result, with a variety of ways of selecting from among them. The social process for teasing out the ethical assumptions will be interesting. My hunch is that exposing each step in the calculation to open review will help in this, but (as you point out) we’ll need much more than just this technology to do it properly.

  7. Hi,
    I also greatly enjoyed David Mackay’s book and the manner in which the scale of the energy issue was highlighted. Following this I created an interactive visualisation based on the calcs in the book. It is available at:


    and is fully open source at the following URL:


    It is not trying to do exactly what you are (ie consistent calculation modelling) but could be an interesting visualisation front end?

    Happy to collaborate


  8. Pingback: Demo-ing Inflo: How much of our fossil fuel reserves can we use? | Serendipity

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