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Sustainable software – how to close the metrics gap

Social Impact & Sustainability

Product & Delivery

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Measuring the environmental impact of your software is a complicated task indeed. In the first of a two-part blog, we look at how best to obtain estimates of software energy use – and how these can provide the basis for improvements in sustainability.

Energy estimates matter

In the quest for more sustainable software, the pursuit of accuracy can often prevent us from making real progress. It's crucial to remember that approximations and estimates are valuable steps toward improvement. By focusing on actionable insights rather than perfect data, software professionals can make meaningful contributions to sustainability.

In the first part of this two-part blog, l look at how obtaining reliable estimates of energy use by your software is the basis on which you can produce reasonable, actionable carbon metrics that can drive sustainability improvements.

A man with grey hair and glasses wearing a black shirt smiles at the camera, a white wall with a window and an orange curtain is in the background

Why measurement is essential

Modern software development relies on a feedback loop of research and data analysis to continually improve and produce high-quality, efficient software. Much like metrics for availability or error rates, we need sustainability metrics to ensure that we’re making our software as sustainable as possible.

Software and hardware have significant environmental footprints, primarily through energy use and embedded carbon. We should also consider water usage, land impact and social effects. As responsible software professionals, we must strive to understand and minimise these impacts, even when they are hidden behind the abstraction of the cloud.

What exactly are we measuring?

For those of us who agonise about the amount of recycling we do, or that flight to Europe, we’re used to thinking about our impact in terms of CO2e per year. So being responsible for 10 tonnes of CO2 output is bad,while less than 1 tonne is great. We think about things in a similar way when working out our corporate carbon reduction plans. How do we do the same for software?

Energy is directly related to carbon. Certainly the more energy you use running your software, the more CO2e you’ll also create, with the amount varying based on the energy mix available to your data centre.

If you can estimate the carbon intensity of the grid at the time you’re running (eg via the electricity maps API) and you know how much energy your software is consuming then you can get a measure of how much CO2e you’ve emitted. Easy, right? Well, it is if your computer is attached to one of these (pictured).

When I first looked into this subject I was amazed how many professionals were advocating running code on a reference computer attached to an energy meter – but it’s actually one of the easiest and most accurate ways to measure the energy use of software (once you’ve calibrated/accounted for the energy use of the rest of the OS/hardware.)

For some teams this will be a decent way of working – try the software on the reference machine and at least you can see when changes result in changes to energy use. However this won’t give you an idea of the real energy use once that software is deployed to the distributed, autoscaled environments most of us are now using.

A photo of a uk plug socket with an energy monitor plugged in and a kettle plugged into that.

Challenges in the cloud

The cloud is essentially a network of physical data centres. Measuring the environmental impact of cloud services is challenging because of the opacity in how data is managed and the varying reporting standards of cloud providers.

Ideally each provider would supply you with easy to consume, highly detailed and accurate carbon use figures that would make it easy for software creators to quickly measure and improve their products, but unfortunately, for a variety of technical and commercial reasons, we are not there yet.

Mostly the hyperscalers’ carbon reporting tools take the form of carbon footprint calculators, using the GHG protocol scopes to give you an after-the-fact idea of how much carbon your service as a whole is consuming.

While some providers give you useful figures, none of them could be said to be comprehensive, timely or even accurate. Instead of relying on this self-reporting, we can also use open source tools such as the Cloud Carbon Footprint tool created by Thoughtworks which can give you more realistic figures but is based on a variety of crowdsourced and unofficial datasets.

Carbon footprint tools are useful in establishing a baseline figure for an existing service, but are less useful for teams who are developing or modifying a service in real time and need to see the impact of the changes they make.

Getting more detailed

Key takeaways

It’s vital that we obtain useful metrics in order to make our software more sustainable

We can get some estimates easily using vendor carbon calculators, though quality is both questionable and data is often incomplete
If we want more real-time estimates of carbon use that can drive software development improvements, we need to use estimation techniques to firstly get figures for energy use and then extrapolate to carbon output.

In the second part of this blog I’ll be looking at how new tools such as a the Impact Framework can make it easier to obtain and automate your carbon metrics, how we also need to include embedded sustainability impacts – and how we can use the same techniques to measure the impact of software on other areas, such as water use.

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Hi Joe, Thanks for letting me know, that sounds great. Completely understand regarding the photos, and it would be great if you’re able to share any approved ones with us for promotional use. Thanks for checking about the LinkedIn posts too — we’d really appreciate being included where possible. Best, Sophie

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