Looking at Yves Marchand and Romain Meffre’s recent photoessay on Detroit, one can’t help but wonder what happened. How did a city that was literally the engine of the American economy sputter and decay into a mass of peeling paint, broken windows, and faded twentieth-century glamour? And on the flip side, how can a city like Dubai, with its Burj Khalifa tower stretching nearly 1 km into the sky, rise out of the desert in such a short period of time?

These are some of the questions that Chris Kennedy’s new book, The Evolution of Great World Cities, seeks to answer. Kennedy is a professor of civil engineering at the University of Toronto with a soft spot for cities and economics. Launching the book in London last week, he noted that he originally wanted to investigate the wealth of cities in much the same way that Adam Smith had done for the wealth of nations. But along the way, the book changed into something subtly different and the result is a fascinating mix of macroeconomics, infrastructure engineering, history, and ecology.

Philadelphia's City Hall

The second theme is the connection between economic growth and the physical structure of cities. Take the automobile as an example. Its introduction in the early twentieth century led to a new mode of urban development, suburban sprawl, which although it has many disadvantages certainly leads to increased consumption. Cars need to manufactured, sold, and serviced; larger suburban homes need to be constructed with more materials and filled with consumer goods. The key issue here is not the infrastructure itself, but the modes of consumption that it necessitates. For example, one might expect that the 1990s IT revolution would have led to a demand side crisis. Just like Smith’s pin-makers, those displaced by the productivity gains of IT – bank tellers, backroom operations, and so on – would be unemployed and unable to consume. However IT also created new opportunities in PC manufacturing, software design, and innovative business models like EBay and Amazon. This new online way of life drove a new cycle of demand, rejuvenating the economy.

To me, this is the book’s most important contribution. This idea of the autonomous consumption of infrastructure, that is the societally mandatory level of minimum consumption created by these systems, is hugely important for understanding not just the economic growth that Kennedy is concerned about, but more broadly the sustainability of cities. North American urban sprawl is a perfect example. While it engenders high levels of consumption, maintaining that lifestyle depends on a throughput of resources, most importantly abundant and affordable transport fuel. Should these fuels become significantly more expensive, these cities would grind to a halt. The same level of infrastructure-mandated autonomous consumption would still be there, but it would now consume a much larger portion of a household’s income, leading to reduced savings, reduced investment in new opportunities, and eventual stagnation. In the language of sustainable development, the autonomous consumption of infrastructure represents a liability that must be serviced on an on-going basis.

The third theme is an analysis of urban economic processes as ecological systems. The relevant chapter offers several noteworthy ideas but it felt incomplete compared to the rest of the tightly-argued book. Nevertheless, an excellent description of Detroit’s decline is provided and the statistics cannot fail to astound: a population decline of 50% between 1930 and today, over 60 square miles of vacant abandoned land (44% of the city’s area), local tree species poking through factory floors that once produced millions of automobiles. Kennedy argues that, in much the same way that an ecosystem needs diversity to survive a changing environment, Detroit was too focused on cars in order to survive, both in terms of the limited diversity of its economy and the inflexibility of its infrastructure. One of the great what-ifs posed by the book is what Detroit might look like now had a 1923 proposal for a subway and integrated transit system been implemented.

Illustrated with case studies on cities as diverse as Toronto and Montreal, Philadelphia and New York, Seville, Paris, Dubai, and London, The Evolution of Great World Cities is a unique work of economic geography. Engineers often complain that economic models are too abstract to offer a meaningful understanding of the real world. Kennedy has therefore done both professions a great service by presenting a strong argument that it is the links between our built environment and economies that matter most.

Chris Kennedy has also written a blog post about the book over at the World Bank’s Sustainable Cities site.

For the past couple years, I’ve been using SVN for version control. It was my first introduction to these tools and it took a while to get the hang of branching, tagging, and resolving the dreaded conflicts. But now it’s an integral part of my workflow and I can’t count the number of times it’s saved my digital bacon.

However I recently switched to GitHub for some of my projects. This was partly out of curiosity, as a number of prominent projects and coders seem to swear by it (Twitter, Hadley Wickham, Kieran Healy). But more practically, I didn’t want to be tied to a single server any more and the idea of a Git repository as a self-standing archive was very appealing.

I’ve now been using Git for a couple weeks and, again, I’ve had to figure out a new mystical language of push, pull, fetch, merge, etc. If you’re familiar with SVN or CVS, the trickiest thing is trying to figure out the Git analogues of all your usual tricks. Git from the bottom up is a fantastic resource in this regard and provides a clear explanation of Git’s internal structure and how to work with it. For more mundane, how-do-I-do-x type things, Github’s Help is very, umm, helpful.

Anyway, all that’s not really here nor there. I mainly wanted to announce my first real Git project: lectures! It’s a collection of LaTeX style files and Python glue to make the creation of both lecture notes and slides much easier. If you’ve used beamer, you’ll know that you can build these two sets of documents from a single source file – provided you’ve got two separate header files. With lectures, all you have to do is write a single source file and run a simple command:

> build-lecture source style


Out pops two PDF files, one for presentation and one with your full notes. There is also support for some basic style configuration. I’ve tried to keep this to a minimum, such as changing fonts (with XeLaTeX for OpenType support) and colours.

Have a go, try the code, and let me know what you think!

PS: I’ve just noticed that a similar project exists called BeamerLecture. Looks like the main difference is that it produces four outputs, hiding answers in pre-class notes, which is a nice feature. The formatting is closer to the beamer defaults though and it doesn’t use XeLaTeX for easy font changes.

We have a new paper out in Energy:

Cities account for approximately two-thirds of global primary energy consumption and have large heat and power demands. CHP (combined heat and power) systems offer significant primary energy-efficiency gains and emissions reductions, but they can have high upfront investment costs and create nuisance pollution within the urban environment. Urban planners therefore need to understand the tradeoffs between limitations on CHP plant size and the performance of the overall energy system. This paper uses a mixed-integer linear programming model to evaluate urban energy system designs for a range of city sizes and technology scenarios. The results suggest that the most cost-effective and energy-efficient scenarios require a mix of technology scales including CHP plants of appropriate size for the total urban demand. For the cities studied here (less than 200,000 people), planning restrictions that prevent the use of CHP technologies could lead to total system cost penalties of 2% (but with significantly different cost structures) and energy-efficiency penalties of up to 24% when measured against a boiler-only business-as-usual case.

The performance of this particular model could be better, as several of the scenario results had large solution gaps which makes it difficult to see the underlying trends. However I think the method we used, applying an integer programming model to design multiple energy systems for generic cities, is innovative and will be of interest to others.

Keirstead, J., Samsatli, N., Shah, N., & Weber, C. (2011). The impact of CHP (combined heat and power) planning restrictions on the efficiency of urban energy systems Energy DOI: 10.1016/j.energy.2011.06.011

Do you cycle to work? How about drive the kids to school? Or maybe hop a bus downtown for an early morning coffee with a friend? Whatever it is you’re doing, these trips all contribute to the carbon footprint of Britain’s rush hour.

I recently analysed these emissions as part of a research project for EDF Energy. The idea was to assess the carbon footprint of rush hour, looking at regional variations in distance travelled, transport mode, and total emissions. If you’re interested in the official results, the study was covered in the Evening Standard, Independent, Business Green and a few blogs, and here’s the official press release. But I wanted to add a few supplementary results here.^*

To calculate the carbon emissions of rush hour, I used data from the 2008 UK National Travel Survey and tallied up all the trips between 700–1000 and 1600–1900. Each trip can be characterized by its distance, purpose, the transport mode used, the location of the trip, and many other attributes. This was the first time I’d used this data set and I was surprised to see just how much information is collected.

For me, the most interesting result was to see how distinct Greater London is from the other British regions. Look at the figures below: loads of public transport, lots of commuting travel, and surprisingly high ownership of gas-guzzlers (band J and above).

Modal share of rush-hour trips. Private transport in red, public transport in blue.

Purpose of rush-hour trips

Vehicle ownership by area type

Another useful plot is the distribution of activities by time of day. You can see here that the evening rush “hour” is more dispersed than the morning rush, with the afternoon school-run starting around 3 pm and heavy travel continuing until about 7 o’clock.

Distribution of daily trips, shaded by purpose

It’s a rich data source and we’ve only scratched the surface. Hopefully we can do some follow-up research to look in detail at variety of trips and their suitability to different low carbon transport options.

^* Of course, these additional comments are my own opinions and have nothing to do with EDF.

In 1959, the mathematician and philosopher Bertrand Russell was interviewed for the BBC programme “Face-to-Face“. At the end of the discussion, the interviewer posed one last question: “What would you think it’s worth telling [future generations] about the life you’ve lived and the lessons you’ve learned from it?” Russell’s answer came in two parts, one moral – about the need to love one another in an increasingly interconnected world – and one intellectual:

“When you are studying any matter, or considering any philosophy, ask yourself only what are the facts and what is the truth that the facts bear out. Never let yourself be diverted either by what you wish to believe or by what you think could have beneficient social effects if it were believed. But look only and solely at what are the facts.”

At first glance Mark Lynas’s new book, The God Species: How the Planet Can Survive the Age of Humans, has nothing to do with Professor Russell. It is ostensibly about planetary boundaries, the nine physical limits which humanity must respect if we are to maintain our current quality of life on Earth. These boundaries – in biodiversity, climate, nitrogen, land use, freshwater, toxics, aerosols, ocean acidification, and the ozone layer – are well-described with clear explanations of the relevant science, the implications of violating the boundary, and the technologies and policies that could help us avoid crossing these limits. Lynas also draws out the links between the boundaries, for example between climate change and ocean acidification, to illustrate both the win-win benefits of certain mitigation options and conversely the negative feedbacks that might occur as boundaries are crossed. There are a few minor presentational niggles – a comparative sentence that uses two units for area, a throwaway reference to declining wood consumption without accounting for fuel substitution effects, the subtitle (do we care about the planet itself or our life on it?) – and like many other popular science books, editors seem to be adverse to including graphs even when something like the Mauna Lua CO2 timeseries with the 350 ppm threshold marked would be a concise illustration of the climate boundary. But overall it’s an excellent introduction to an emerging and important way of viewing global environmental issues.

But in many ways, the real story of The God Species is Lynas’s re-discovery Russell’s maxim (knowingly or not). Lynas has been a devoted environmental campaigner for years and throughout the text, he is at pains to point out that the planetary boundaries view of environmental problems means adopting solutions that mainstream environmental groups may find hard to swallow. For example, discussions on the potential of nuclear power, genetic engineering, or geo-engineering include lines such as “I know many environmentalists will read all this with a sense of growing horror. A technofix! How outrageous! What a cop-out!”. While Lynas’s pragmatic view is to be commended, I found the “you’re not going to like what I have to tell you…” tone somewhat distracting. It felt as though the reader had missed out on a long and tormented backstory, like catching a bitter passing aside between two ex-lovers at a party.

The God Species, then, has the feeling of two strong themes shoe-horned into one volume. The first subject, the science of planetary boundaries, is fascinating and the author brings these issues to the attention of a wider audience with a deft touch. But a longer treatment would permit a more detailed discussion of the science and the suggested solutions. For example, the discussion on the sustainability of economic growth would benefit from reference to Bill Nordhaus, William Ayres and others in the resource economics literature. Similarly, when assessing the role of privatisation in the delivery of freshwater, the choice is presented as a fairly strict dichotomy between “efficient” private and “inefficient” public provision without really getting into the role of institutions and regulations to ensure that either system works effectively. More detail on the science of how planetary boundaries are identified and monitored could also be valuable.

The second theme, on the environmental movement’s selective use of scientific data, also deserves more attention. Lynas hints at this in the last chapter, providing a fascinating eyewitness account of the Copenhagen climate negotiations (see also this Guardian piece), but a more detailed analysis of how environmental groups have painted themselves into corners on climate change and other issues by arguing against politically feasible outcomes for the sake of environmental purism would be literary and political dynamite.

But perhaps that’s something for Lynas’s next project. On its own terms, The God Species is an excellent introduction to a new pragmatic way of looking at the environment, one that as Russell noted is supported only by the facts and “the truth that the facts bear out”.

‘The God Species’ by Mark Lynas is published by Fourth Estate on July 7th and is available for pre-order from Amazon.co.uk

About a year ago, I wrote a paper with Niels Schulz that asked what is unique about urban energy policy. We looked at London specifically and found that, although the Mayor’s office and local boroughs were keen to act on climate change and energy issues, they had very limited means at their disposal. Policy making by nation states or regional authorities, for example, might involve heavy-hitting economic policies such as carbon trading, renewable portfolio standards, or minimum product standards. But as open systems located within these other domains, a city like London can really only encourage citizen awareness of the issues, improve local transport, and try to attract low-carbon investment.

For a number of years now, the C40 Cities network has brought together concerned cities to try and overcome these obstacles by providing a forum for sharing best practice and establishing a visible constituency that can engage with other policy process; witness for example the C40′s presence at the Copenhagen climate conference in late 2009.

But one of the most valuable lessons from the C40 is that every city is different. There is no such thing as a one-size-fits-all urban energy and climate policy and a recent report by Arup demonstrates this nicely. Arup distributed a questionnaire to all C40 cities in March and April 2011, asking in particular about mayoral powers in different sectors such as transport, energy supply, water and waste. As shown in the figures below, most cities own and operate their water networks but their control over waste, transport, and energy use in buildings is highly variable.

Results of C40 survey on mayoral powers over water

Results of C40 survey on mayoral powers over waste

Results of C40 survey on mayoral powers over transportation

Results of C40 survey on mayoral powers over energy use in buildings

Perhaps the most significant finding is that many C40 cities have limited control over their energy supply systems and instead must rely upon “setting visions” in hopes that this will influence the relevant policy makers:

“The main sources of greenhouse gas emissions from urban areas are generated by the consumption of fossil fuels. In general, C40 cities did not register strong powers in the energy supply sector, reflecting the fact that most energy supply infrastructure is controlled by state, regional, or central governments. The strongest powers cities reported in this sector are related to the ability to set vision, which can be used to unofficially influence higher levels of government who hold most of these powers. Nevertheless, C40 cities have implemented 268 actions to create low carbon energy supply.”

The ability of cities to control their own finances is also constrained, with most relying upon government transfers or property taxes.

Results of C40 survey on mayoral powers over finances

These results point to a single, perhaps slightly boring, answer: that local context greatly affects what cities are capable of achieving in terms of energy and climate policy. And the corollary of that is that they will need to establish networks with other levels of government, private sector partners, and civil society groups if their ambitious goals are to be achieved.

Keirstead, J., & Schulz, N. (2010). London and beyond: Taking a closer look at urban energy policy Energy Policy, 38 (9), 4870-4879 DOI: 10.1016/j.enpol.2009.07.025

Last week was the biennial conference of the International Society of Industrial Ecology, held at the lovely University of California Berkeley. At four days, plus an extra workshop for the Sustainable Urban Systems section, it was a long event but the week went quickly with a number of excellent talks and interesting attendees. Here are some of my highlights:

• Various (Manfred Lenzen’s group), University of Sydney. One of the most popular techniques at the conference was environmentally-extended input-output analysis, i.e. the use of trade data to determine how the consumption of finished goods and services drives upstream resource consumption. The Sydney group are developing a comprehensive tool called Eora which will offer data at much higher resolutions than previously available: 160 countries, 20 to 500 sectors, 5 sets of prices, 2000–2009 time series data, and 34 auxiliary indicators. It’s a massive computing project too, involving an optimization problem of 509,987,242 variables, 6.6 million constraints, and an 8 GB result file.
• Marian Chertow, Yale. A pioneer of industrial symbiosis, Prof. Chertow’s talk examined the slow uptake of these ideas using the language of market intermediation and behavioural economics. Industrial symbioses typically involve by-products and the associated markets can be small, informal and driven by tacit knowledge, hence the need for market intermediaries to identify opportunities and facilitate transactions. From the behaviour economics side, four ideas were identified as barriers to change: the status quo bias, the bystander effect, prospect theory and framing, and the planning fallacy.
• Various (Igor Nikolic’s group), TU Delft. The researchers at TU Delft always present interesting work and this conference was no exception. Among the projects discussed were: the excellent Enipedia, a semantic wiki application for describing global energy systems; an application of the tool to a case study in the port of Rotterdam; an agent-based model to study the planning and operation of the Dutch electricity grid under climate scenarios; and an agent-based model of the metabolism of metals in mobile phones.
• Various, University of Toronto. Chris Kennedy’s Sustainable Infrastructure Group presented a number of good talks including: a model for designing “satellite” district energy systems (where network expansion incorporates the boilers of each building, rather than relying on a single central plant); the PURGE model which uses technology diffusion curves to estimate Pathways to Urban Reductions in Greenhouse Gas Emissions (see also Carbon City Planner); and two models looking at heating and cooling in buildings, and the thermodynamic performance of cities.
• Clemens Deilmann, IOER. Data envelopment analysis is an efficiency assessment technique usually applied by the regulators of natural monopolies, such as electricity networks. However Deilmann and colleagues applied it to the ecological and environmental performance of 116 German cities. The results weren’t entirely surprising – “efficient” cities are those of medium population size, with lower levels of debt and more doctors per capita – but it’s an interesting application of the technique.
• Julia Steinberger, University of Leeds. In one of the last talks of the conference, Dr Steinberger gave a high-level overview of the links between economic performance and resource efficiency, and tackled the question of CO₂ sufficiency (i.e. how much CO₂ is needed for a “good” life?). She had two graphs that were particularly interesting. In this first one, you can see how over time countries have been able to achieve higher standards of living (as measured by the human development index), with successively less energy and carbon (Steinberger and Roberts, 2010).
  

  Figure 1: Data and regressions of HDI and energy consumption (upper plot, 80 countries), carbon emissions (lower plot, 93 countries) from 1975 to 2005.

  The second plot, which I can’t find a copy of, was a nice comparison of national carbon emissions from both production and consumption based perspectives.

For my part, I presented some of our recent work on how activity-based modelling can be used to simulate urban resource demands at high spatial and temporal resolutions.

The conference also marked the first time that I have used Org-mode for taking notes and I can highly recommend it. The simple way of thinking in outlines naturally fits a conference format, and you can fold away unused parts of your notes to get a clear workscreen. Even better you can add tags for subject categories, TODOs, and insert hyperlinks, making it easy to review your notes later and find what you’re looking for. It’s likely to be my main note-taking tool for years to come.

Steinberger, J., & Roberts, J. (2010). From constraint to sufficiency: The decoupling of energy and carbon from human needs, 1975–2005 Ecological Economics, 70 (2), 425-433 DOI: 10.1016/j.ecolecon.2010.09.014

I’ve had Malthus on my mind recently. You know, the Reverand Thomas Robert? Author of An Essay on the Principle of Population and probably the strongest candidate for a grandfather of environmental pessimism? I’m not sure why he’s become such an obsession but it probably has something to do with the proliferation of recent newspaper and magazine articles on the subject (1,2,3).

The Reverend Thomas Malthus

Malthus’s most famous observation was that population growth is geometric but food growth linear, from which he concluded that Mother Nature had to intervene from time to time with famine, pestilience, and war in order to keep numbers in check. By framing it as a seemingly immutable mathematical law and by speaking to contemporary debates on industrial age poverty, Malthus’s ideas were hugely influential at the time and continue to shape modern discussions about Limits to Growth and resource scarcity.

In a nutshell that’s the story of Malthus, at least the one that everyone is familiar with. But I figured that, like Adam Smith, his message must have been telescoped and compressed over the years so that any subtlety in the original argument is gone. So I want to go back and look at the original material for myself, to understand where Malthus’s ideas came from and to better judge the extent to which they speak to today’s problems.

This will be a long-term project but to get started, I found an excellent primer on the history of Malthusian ideas. The book is called From Malthus to the Club of Rome (1994) by Paul Neurath, and its first chapter covers the early history of demography up to Malthus. What follows is a very brief precis:

• “Classical Malthusianism” Nearly all of the usual suspects in ancient philosophy had something to say about population including Confucius, Plato, Aristotle, Ibn Khaldoun, and so on. The surprising thing is that this early work seems to have been primarily motivated by public administration concerns, i.e. what’s the right size for a population in order to be able to rule effectively, or at the very least, to avoid having a bunch of starving peasants knocking down your door.
• In the Middle Ages, no one worried about population, mainly abiding by the Biblical dictum to “be ye fruitful and multiply”.
• In the 17th century, as cities grew from the Renaissance and into the Industrial Revolution, writers began to respond to the changes around them. Two broad schools of thought emerged. First, in Germany and England, a community of amateur demographers and professors began collecting church statistics and describing the dynamics of population change in different countries. These scholars didn’t worry about resource consumption per se but did introduce a number of methodological innovations, such as mortality tables. Meanwhile in France, with its strong central administration, matters of population were matters of state. Jean-Baptiste Colbert, minister of finance, and others promoted a merchantilist population policy, encouraging growth through a range of fiscal and social measures in order to increase the state’s power. Power in two senses: both creating fodder for the army but also creating workers who could increase production, exports, and reserves of gold and silver.
• Finally another strand around this time were the theologians, such as Johann Süssmilch, who sought to interpret population changes as part of God’s plan. Süssmilch is particularly interesting as he calculated perhaps the first estimate of the world’s total carrying capacity, a very precise 13.92 billion.

Neurath’s essay is driven by an interest in the history of demography. He traces innovations in methods, theory, and the links between demography and other emerging social sciences. The essay only tangentially touches upon resource consumption but still, there are a few relevant ideas that need to be followed up.

1. Rates of technological change Neurath observes somewhat indirectly that the power of Malthus’s idea is that, given the shape of the population and resource curves, the relative rates of increase might be such that balancing supply and demand would be impossible even with technological improvements. This is similar to modern questions about the rates of investments in oil exploration and production. (See my last post for a nice quote on this.)
2. Trade and the geography of scarcity. Only a few of the sources Neurath cites are explicit about the geography of scarcity, in other words, can a local imbalance of supply and demand be corrected by trade flows? If this was a major strategy for alleviating resource constraints historically, then it makes the global scale of current economic activity all the more challenging as there are no extra-terrestrial trading partners available.
3. Maximum carrying capacity Süssmilch’s estimate of the Earth’s total carrying capacity echoes attempts to map planetary boundaries now. The question is whether such an exercise is possible or useful.
4. Standards of living. A related point is how these authors deal with standards of living. It’s one thing to feed all the world’s mouths, it’s quite another to have everyone feasting.

I’m slowly pulling together a pile of reading on this topic and will post again once I’ve chewed through it.

I’m reading a fantastic book right now called From Malthus to the Club of Rome and Back, a collection of essays on demography and resource consumption by Paul Neurath. There have been lots of quotable lines, but this one in particular caught my eye:

I have no quarrel with those who expect that some day we shall be able to irrigate the Sahara desert and farm the Amazon basin or the Congo basin (except to ask what effect cutting down the rain forests may have on man’s ability to survive on this earth), or that we shall be able some day to dig minerals out of the earth through shafts three and four times as deep as the deepest today. But I do have some quarrel, or at least some serious questions, with those who take it for granted that we shall be able to accomplish all of this within the short time left, some 100 to 120 or maybe 130 or so years, while mankind grows at current rates from its present size of 4 billion to some 30 to 50 billion – that is, unless we heed the warning of the model makers and others, that mankind simply cannot keep up for long its current 2 percent per year rate of growth, and its current ever-growing rate of consumption of irreplaceable materials. My quarrel is with those who take all of this for granted on no better basis than their own optimism and the fact that so far mankind has indeed managed – neglecting to heed the fact that through most of its history mankind managed with very small growth rates, that even as recently as 300 years ago, the growth rate amounted to only some 3 to 5 per 1,000 per year, compared with our current 20 per 1,000, and in fact in wide regions of Africa, 30 and 35 and more per 1,000 per year. (p. 81, 1975)

The numbers have of course shifted since this was originally written over 35 years ago (current global population growth is approximately 1.16% per year). But the main point is that the pace of change is the key factor, not whether hard limits to growth exist but whether we can adapt and innovate in time.

Last week, I talked about how to conduct a quantitative literature revew in R and the data set I used came from a paper that I’m working on with some colleagues. We’re trying to review the current state of urban energy system modelling in order to figure out what works, what doesn’t, and what comes next. The paper’s working title sums it up nicely: “A review of urban energy system models: approaches, challenges, and opportunities”.

When we started the paper, we had a rough idea of what we meant by an “urban energy system model” but it wasn’t articulated very well. We figured that there would be some demand-side stuff on estimating demands for electricity, gas, and transport, and maybe something about the optimized design of energy supply systems. However now that we’ve done most of the review, I can say with some confidence that there are six main categories of urban energy system model:

• Technology design These models focus on the design of single urban energy system technologies such as vehicles, heating or cooling system components, and renewable energy technologies. The literature seems to emphasise supply-side technologies – that is, we didn’t see much about demand management, insulation, or anything like that – and the studies are conducted using a mix of simulation and experimental methods.
• Building design Moving up the spatial scale, building design models look at the performance of building systems typically on a monthly or annual time frame. Like technology design models, simulation methods are the most common. However unlike technology design models, the focus is largely demand-side, namely how building design affects demands for heating, cooling, and lighting.
• Urban climate A related sub-category are the urban climate models. These studies use street cross-sections or fine-grained regular grids to assess changes in urban temperature over the course of a day. Applications might be concerned with pedestrian comfort on a street or calculating urban heat island effects. By simulating external temperatures, these models should play a key role in urban energy modelling; however the energy implications of these temperatures are rarely considered.
• System design These models use optimization methods, rather than simulation, to assess how different energy supply technologies can be combined to meet a set of user-specified energy service demands. They focus largely on a district scale, looking at static or yearly timeframes.
• Policy assessment Policy models examine the whole city on an annual or decadal timeframe and try to assess how long-range policy goals can be met. For example, these models might use optimization techniques to determine which technologies could meet a given carbon target most cost-effectively, or they might use simulation to explore the potential impacts of a policy change. A large number of descriptive case studies were also found in this category.
• Land-use transportation Searching for “urban energy system model” doesn’t actually turn up very many LUT models, but land-use and transportation processes are key to understanding overall urban energy demands (as well as supply side possibilities). We therefore did some additional searching to examine how these models, which typically simulate the daily behaviour of heterogenous individual agents through the city, can be used to calculate energy demands.

We’re now writing the final sections of this paper and hope to submit it during the summer. In due course (months, years?) I’ll post again with a link to the full paper.