POD! On YIMBY Pod this week, Martin finally takes the Claude pill and I try to persuade him of the need to build data centres – and we speak to the excellent Jonn Elledge about his new book, on the 31 Inventions That Build Our World! Listen here, or wherever you get your pods.
I’ve fallen into a self-destructive feedback loop.
No, I haven’t started drinking or experimenting with drugs. I’ve been doing something much worse: I’ve been clicking links to news articles on Facebook.
We should all know by now that this is a deeply unwise thing to do, because of how the algorithm works. It doesn’t select what to show you based on what is important or useful to your life, and it has long given up showing us things our friends have posted. Instead, the algorithm optimises for engagement – whatever keeps us clicking and scrolling the longest.
And unfortunately for me, that means a constant slew of articles and comments complaining about proposed data centres, usually published in the Guardian.
So now my morning routine is wake up, pick up my phone, load up Facebook, and find myself raging mad before I’ve even got out of bed.
Though in fairness to me, this isn’t just because I have a deeply dysfunctional relationship with my phone. It’s the Guardian’s fault too, as some of the claims the paper has been making about data centres are not exactly wrong… but they are lacking significant context in a particularly annoying way.
And this is something worth getting a little mad about. I wrote a couple of weeks ago about how we need more data centres for reasons of national security, and if you buy my argument, then we need to be rational about the trade-offs involved in data centre construction.
So this week, I want to focus on three recent Guardian data centre stories, and why it’s actually a little more complicated than they first appear.1
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1. Flights of fancy
Let’s start with a story that the Guardian ran last month, which was originally headlined “Proposed London datacentre will have annual carbon footprint of 27,000 flights to New York”.
The piece focuses on the proposed East Havering Data Centre Campus (EHDCC) in North Ockenden, on the outer edges of London, and it claims that:
The 1.2m tonnes of CO₂e the EHDCC expects to emit would amount to 26,795 long-haul flights from London Heathrow to New York’s John F Kennedy international airport, according to the UN’s International Civil Aviation Organization’s carbon calculator.
Unfortunately though, it appears that someone screwed up the calculation – as the story was later revised and it instead puts the estimated emission at the equivalent to 8,480 flights instead, which the Guardian notes in a correction.
However, this isn’t actually my problem with this story. Flight emission calculations are always going to be shaky, as calculators necessarily make a bunch of assumptions that can steer numbers in wildly different directions. For example, the UN calculator linked in the excerpt clearly does a distance calculation, as it asks for departure and arrival airport – but it isn’t concerned about the type of aircraft that actually flies the route, even though that too can make a significant difference.2
But anyway, none of this matters, because what I’m more bothered by is the claim that sits behind that: the idea that the new data centre campus will lead to an additional 1.2m tonnes of CO2 emissions every year, because once you dig into how it was calculated, things start to get extremely weird.
So where did the 1.2m come from? Surprisingly this wasn’t (or doesn’t appear to have been) provided to the Guardian by an anti-data centre activist group, but it’s a number taken from the actual planning documents provided by the actual developer.
So, case closed, right? Well, I don’t think so – and to explain why, we need to do some maths.
Summing up the problem
In total, the completed EHDCC is expected to be a 600MW campus in total. Data centres are measured in terms of energy usage rather than, say, processing power, as ultimately that is what matters more. The chips will be replaced every few years with something a little faster, so what really matters is how much energy is used by the site, which is more fixed.
To start then, if you look at Technical Appendix 14.1 of the planning documents, you’ll discover that the developers started by taking the technical characteristics of a representative 50MW data centre and basically scaled it up. So all of the sums were done for 50MW to start with.
Then we reach the first choice the modellers have made. There’s basically an implicit assumption throughout the calculation that the data centre will be working at 100% capacity 24/7 throughout its lifetime. This is something the government has disputed in response to criticisms of other data centre projects, but I think this assumption is fair enough to make, at least when modelling energy usage. If AI is as transformative as it appears to be, the demand for inference is going to be almost limitless.
So we start with 50MW of usage – but in reality a ‘50MW’ data centre will actually use more than 50MW of energy, as the headline figure refers only to the energy used by the computers crunching the data, and not the supporting infrastructure like air conditioning, lights on the ceiling, or the microwave in the canteen.
So to account for this, in the modelling the 50MW figure has been multiplied by 1.326 – what is known as the “Power Usage Effectiveness” ratio. This multiplier just comes from the reference figures for an equivalent data centre. So really, according to the reference data, a 50MW data centre should expect to use 66.3MW of electricity.
And then we have to multiply it again to turn that into a prediction of annual energy usage. So we multiply 66.3MW by 24 hours a day and 365 days a year, which gives us approximately 581GWh of electricity usage in any given year. Phew!
But we’re not done yet – now we have to work out how all of the energy usage translates to emissions.
The technical appendix says that to work this out, the developers have used a figure of 0.14kg of carbon emissions per kWh, from the government’s Standard Assessment Procedure (SAP 10.2), which is, well, a standard used across the construction industry for estimating emissions.
So next we have to do a bunch more multiplication, to come up with an emissions estimate:3
581GWh/year of energy usage in a 50MW data centre
multiplied by the expected design life of 60 years
multiplied by 12 data centres on the campus
multiplied by 0.14kg of carbon per kWh
= an estimated 58,564,800 tonnes of carbon emissions over its lifetime
= or an estimated 976,080 tonnes of carbon emissions per year
Now, mathematicians reading will note that the final figure – roughly 1m tonnes when rounded up – is still less than the scary-sounding 1.2m tonnes figure. So what about that last little bit?
Unfortunately there isn’t a clean calculation page in the planning documents, but the developers do say that an “uncertainty factor of 15% has been applied to the carbon intensities”, which would bring us to around 1.12m tonnes per year if this is what has been done here.
Then finally, on top of this there are a few extra components added on to the calculation. The developer’s model also takes into account ‘embodied’ emissions from construction, but on the flip side it also negates some emissions by taking into account the fact the build-out of the campus will be phased and that the full site won’t be up and running until 2043.4
And that’s what gets us to approximately the average figure of 1.2m tonnes per year figure published by the Guardian. Phew.
Insane assumptions
Now, this sounds super comprehensive, right? I’ve described an incredibly detailed model of the emissions, running to dozens and dozens of pages in the planning documents. It certainly has the appearance of being thorough and thoughtful.
But did you spot the deeply strange assumption that has been baked into this calculation?
That’s right, it’s that 0.14kg of carbon dioxide per kWh. For the sake of the calculation it is treated as immutable, even though it really shouldn’t be.
And the technical appendix inadvertently makes it clear why this, in my view, is a massive flaw in the maths. It says that:
“Future Energy Scenarios which predict future decarbonisation of the electricity grid have not been applied.”
In other words, this entire carbon calculation is based on the idea that over the next six decades Britain will not decarbonise any further than it has now. Which would obviously be an absolutely mental assumption to make.
If the 0.14kg stays constant, it assumes that Britain will not reduce the carbon load on the grid by building any more wind farms or solar panels. It also assumes that two major nuclear plants, Hinkley Point C – and Sizewell C – will not come online, even though the former is half complete. It seems to assume that we will not increase the proportion of renewable energy on the grid from now until I am 99 years old in the year 2086.5
In other words, what’s happened is that for some reason the developers have deliberately modelled what they call in the documents a “reasonable worst-case scenario”, and the Guardian has run with it, without mentioning this worst-case caveat, even though the odds of it actually happening are basically zero.
So what will EHDCC’s emissions be instead? It depends on how aggressively we decarbonise the grid – but I’m very confident that it will be significantly less than the worst case scenario, especially if the government continues to achieve its decarbonisation goals and (more importantly) the costs of solar and battery storage continue to dramatically fall.6
Now, I don’t blame the developers for doing the calculation in this way. Presumably they had no choice7 – otherwise you’d expect developers to pick the most optimistic numbers possible.
But once you step back and take the time to think about it, as the Guardian probably should have, it strains credulity. And to pretend otherwise is not going to help readers form an accurate picture of the world.
2. Water use
Now let’s turn to a story the Guardian published in July, titled “Not enough water for UK’s datacentre plans, trade body says”.
Water UK, the trade body that represents water companies in Britain and Northern Ireland, said in a publicly available written briefing to MPs that the government’s water forecasts were “fatally flawed” and “explicitly exclude” datacentres.
It wrote that the government “makes not a single mention of water” in its policy for delivering AI growth zones, its AI for science strategy or its AI opportunities action plan.
There are plenty of legitimate reasons to be sceptical or even mad about the AI buildout. The implications of the technology are uncertain, and despite the nonsense in the first section, it is true that AI data centres use a non-trivial amount of electricity in their operations, which we need to plan for.
But there’s also a lot of bullshit too. Water usage for cooling data centres is one such example – a fear that has been consistently debunked by people like Andy Masley.
So that’s what makes this story so interesting – it’s the water industry itself seemingly, er, wading in, with its concerns about building more data centres. Perhaps it suggests there is something to worry about after all?
However, I think what is missing here is some pretty vital context, which should change our perception of just how big a problem this is.
But before we get to that, what do we know about AI water usage specifically? As Water UK notes in the briefing for MPs linked above, there are two factors that can dramatically change how much water a data centre uses.
First, whether or not the building uses an ‘open-loop’ or ‘closed-loop’ cooling system matters. An open-loop system ingests water, cools the servers and then the heated water evaporates in a cooling tower back into the atmosphere. This means it requires a constant supply of new, fresh water to operate.
Closed-loop systems, however, recycle the water they use. The water is heated by the computer equipment, but it is retained and cooled so that the same water can be used over and over again. This is obviously a much better way of doing it, as fresh water is only occasionally used to top up the system. The data isn’t great, but it appears that most UK data centres are thought to use this sort of cooling system – or have no water cooling system at all.
Then we get to the second reality of data centres in the UK, which Water UK also notes in its briefing. Water usage is highly dependent on climate. A data centre built in a desert will require far more water cooling than a data centre built in a rainy and grey Scotland. And in fact, this means that in Britain, water cooling systems simply won’t be switched on for much of the year anyway. According to TechUK, 64% of surveyed data centres use less than 10,000m³ every year, which the organisation says is less than a typical leisure centre.
Though to be clear, this doesn’t mean there isn’t a small, legitimate challenge here. According to Water UK, the problem is that even if demand for water cooling only kicks in on hot days, that’s exactly the same time when demand peaks more broadly, as everyone wants to keep cool by consuming water at the same time. So more data centres will conceivably exacerbate the peaks.
So what’s missing? Why am I complaining? Doesn’t this all seem pretty reasonable to report? On one level, perhaps – but it also has a severe lack of context.
I really recommend reading this excellent piece by Rowland Manthorpe,8 who has been investigating water usage in British data centres for some time.
In his piece, he looks at two scary-sounding stats on water usage – one of a Scottish data centre that reportedly uses 27m litres per year, and an estimate published by The Times that data centres in the Thames Water region use 10bn litres per year. That sounds dramatic, but it works out as just 0.005% and 0.2% of the water supply respectively.
So even if we multiplied the number of data centres and the water they were using many times over, it would still be a microscopic proportion of overall water usage.
And this is ultimately the problem with the Guardian piece too: it doesn’t mention the denominator. To go back to Water UK’s briefing, it says there are 14 billion litres of water supplied every day and data centres currently account for 6.6 million of those litres – so around 0.047% of Britain’s daily water usage. So this is all to say that ultimately, compared to everything else, data centre water usage is basically a drop in the ocean.9
3. What the FOI?
The final story I want to look at is the most recent – as it’s very, very silly.
“UK government does not know what datacentres are being used for, FoI request shows”, reads the Guardian headline, and the story sounds pretty damning:
When asked in a freedom of information (FoI) request who was using the largest sites and what for, the Department for Science, Innovation and Technology said it did “not hold the requested information”.
Sounds bad, right? But the reality is that this appears to be hilariously tenuous.
The story begins over a year ago, on the 25th August 2025, when Oliver Hayes from a charity called Global Action Plan submitted the following FOI request to the Department of Science, Innovation and Technology (DSIT):
Dear Department for Science, Innovation and Technology,
Please confirm whether you hold information on the companies, organisations or bodies currently using the UK’s largest (more than 15MW of rated IT capacity) data centres and the purposes for which they are used.
If this information is held, please provide a list of these businesses and purposes. If it is not possible to provide details on individual companies, please try to provide a breakdown of the types of companies, organisations or bodies accessing the UK’s data centres and the proportion of the UK’s data centre capacity that these types of industry currently utilise.
Thank you in advance for providing this information,
Oliver Hayes on behalf of Global Action Plan
The department then responded on the 12th September last year, confirming that it does not hold the requested information.
And what you might not realise unless you’re the sort of weirdo who sends FOIs regularly is that this is actually a pretty narrow response.
The way the Freedom of Information Act works is that anyone can request information from a public body or government department – but only if a document containing that information already exists.
In other words, all this response is really saying is that there is no document that exists in the department which contains a list of data centres in a table alongside the businesses that use them and for what purpose.
So it’s less of a damning response, and arguably more Hayes encountering a deliberate friction hidden within the law. Yes, information is free, but you have to know what you’re looking for first.10
And as much as it pains me to say, as someone who regularly sends FOI requests, this makes a lot of sense. If any random member of the public could write in and essentially task civil servants with a homework assignment to put together a new document for them, the business of government would quickly become unworkable.
But anyway, let’s be more generous and assume that DSIT doesn’t actually hold the information at all, in any form. My next question is… so what? I can’t quite work out what response Hayes was expecting it to reveal or why it would be particularly useful for the government to know that, say, Netflix is using capacity in one of Amazon’s data centres, or OpenAI is using capacity in one of Microsoft’s.
So I think what this story really is more than anything is just a spectacular PR success on the part of Global Action Plan. With an extremely thin justification – an FOI with a boilerplate non-response, sent over a year ago – they’ve managed to get their talking points published as a big story in a major news outlet, on the strength of basically nothing. Bravo!
Facts x Importance = News
So there are three stories about data centres and why they make me mad. Like I say above, none of them are false, exactly. But in each case, scary-sounding numbers and facts become significantly less scary once you add a little context – and the reason I’ve spent several thousand words banging on about this is because I think this really matters.
As has become clear from the coverage, data centres are a new, salient dividing line in politics, and are fuel for the next round of the culture wars. If we’re going to navigate the build-out successfully, we’re going to need to be working from a common set of facts about the world – and we should want news coverage to clearly explain the real trade-offs involved in both building and not building.
And I should probably spend less time on Facebook getting mad.
Phew, another long one this week. If you enjoyed reading this then make sure you subscribe (for free) to get more like this in your inbox. Or take out a paid subscription if you really value my work. And if you’re from the Guardian, please don’t break my legs.
Something annoying when writing about data centres is that there isn’t yet a society-wide consensus on whether it is “data centre” or “datacentre”. I’m wildly inconsistent on this myself, but I’ve tried to go with “data centre” unless it’s quoting someone else.
I’m not an expert, but LHR to JFK is flown by a tonne of different aircraft, and a modern plane like JetBlue’s A321neo is apparently more efficient on a per passenger basis than, say, an old British Airways 777-200.
Please, Substack, let me add tables into posts!
It also negates some of the emissions from the final total because the plan is to recycle the heat generated by the data centre as district heating to heat a nearby horticulture building, which won’t need to use gas boilers because of it.
I guess it even implicitly assumes that in 2042 the diggers and generators on the construction site will still be using diesel and won’t have gone electric too.
I also think the premise of the story is a bit weird, given that unlike other controversial data centres, this won’t be powered on site by gas. It won’t even have gas backup generators, as the plan is to use hydrotreated vegetable oil instead (which will release carbon, but not carbon that was first sequestered millions of years ago). It will just plug into the national grid, and use whatever energy is available on there. So it’s really getting mad at something that isn’t directly the developer’s fault anyway.
The developers say they did the calculation per guidance from the Royal Institute of Chartered Surveyors, so this is basically the professional standard.
If I were more conspiracy-minded, I’d definitely point out how convenient it is for the water industry to have a boogeyman in the form of data centres, that might draw some attention away from just how much water is lost every day from leaks on the water network.
For example, when I wrote my exposé of TfL’s trial use of AI cameras a few years ago, I sent in an FOI pretty confident there would have been some sort of report evaluating what they could do, because it was publicly announced that there would be a trial.
But if TfL hadn’t written up a report, and had just used the cameras, or had only talked about how effective they were during an in-person meeting, if I’d sent in an FOI request asking the same thing, they could have quite legitimately given me the same response that DSIT gave Global Action Plan.