Technology underpins virtually every aspect of business operations. The environmental impact of our software systems is becoming impossible to overlook. With IT contributing approximately 4% of global greenhouse gas emissions—a figure set to rise dramatically in the coming years—the sustainability of our digital infrastructure deserves urgent attention. How can we slow - and reverse the pace of energy and resource consumption required by our digital infrastructure, hard and software?
To explore this critical intersection of technology and sustainability, we sat down with Carsten Windler, Plan A’s Director of Platform, and expert in sustainable software engineering. In this conversation, we look at how companies can reduce their digital carbon footprint while potentially improving performance and reducing costs, with real solutions that can be implemented today.
Carsten Windler is the Director of Platform at Plan A, Europe’s leading corporate carbon accounting, decarbonisation, and CSRD reporting software provider. The native German holds a Diploma in Business Administration and Management and has more than 17 years of experience in IT consulting and software development. Prior to Plan A, he worked as CTO and Head of Engineering in various prominent German tech companies.
Understanding green IT and its business benefits
"Green IT aims to reduce the carbon footprint and electronic waste through carbon-efficient software and sustainable resource management," explains Carsten. While sustainable IT encompasses hardware lifecycle management, including using refurbished products, extending product lifespans, and prioritising energy-efficient equipment, Carsten's focus is specifically on making software more carbon-efficient.
But why should businesses care? According to Carsten, the benefits extend well beyond environmental impact:
"Software built with sustainability in mind will reduce carbon emissions and lead to considerable cost savings. This is particularly true if your software is operated in the cloud, where resource consumption is precisely tracked and billed."
Performance improvements represent another significant advantage. "A lightweight website ranks better in SEO, and fast-loading websites are known to have better conversion rates," Carsten notes, highlighting how sustainability initiatives can directly impact business outcomes.
Measuring software emissions: a critical first step
Before implementing sustainability improvements, establishing a measurement baseline is essential: "Before you start optimising the software's efficiency, you should be able to measure its carbon footprint first. Otherwise, you can't evaluate the impact of your efforts appropriately."
For local systems, direct measurement using watt-hour meters provides accurate readings, although this approach requires controlling for background processes. More sophisticated options include software solutions such as Green Metrics Tools or GreenFrame for containerised applications.
Cloud-based applications present a different challenge. "We obviously can't use power monitors for applications operating in the cloud. We need to rely on the data that the cloud provider gathers," says Carsten. While major providers like AWS, Google Cloud, and Microsoft Azure offer carbon footprint reports, these often come with limitations:
- Non-standardised reporting formats
- Focus on market-based rather than location-based emissions
- Delays of up to three months in data availability
- Excessive use of proxy data which leads to too great inaccuracy.
Carsten recommends the Cloud Carbon Footprint tool (CCF) as a solution: "It uses the cloud usage data it receives via APIs to generate accurate emission estimates. This way, the tool can provide nearly real-time data about your AWS, Google Cloud, or Microsoft Azure account emissions, making it the perfect tool to start your optimisation journey."
The sustainable software engineering framework: a five-level approach
Carsten outlines a five-level framework for reducing software emissions, beginning with the most accessible, high-impact changes and progressing to more complex transformations.
Level 1: Infrastructure optimisation
The first level focuses on infrastructure adjustments that deliver significant emissions reductions with minimal code changes.
"Before optimising your code, you must ensure your infrastructure is not wasting resources," Carsten advises.
Carsten points to possible opportunites to start fast and limit dead ends.
Remove unnecessary resources
"Over time, systems tend to become cluttered, services get replaced but not immediately deleted and eventually forgotten, or recurring jobs are no longer required but continue to run unnoticed" Carsten continues.
These "zombie" servers—inactive but still consuming energy—represent an easy win for emissions reduction.
Rightsize your infrastructure
Cloud environments make overprovisioning common, but Carsten points out that "finding an instance size that leads to high utilisation without reaching its boundaries" is crucial due to energy proportionality—the principle that servers consume significant power even at low utilisation levels.
For variable workloads, Carsten recommends either "burstable instances" for brief usage spikes or implementing autoscaling for more significant fluctuations.
Collect your garbage
"Data at rest is another emission source worth considering," Carsten explains. "Cloud storage is exceptionally cheap, so it is tempting just to save data there and forget about it. However, the data must still be stored on physical drives, which must be produced, shipped and hosted in data centres."
Implementing retention policies that automatically delete unnecessary data after specified periods can substantially reduce this footprint
Level 2: Architecture improvements
The second level explores how software components interact, requiring moderate code changes to achieve significant emissions reductions.
Microservice architecture
"A small service is easier to scale than a monolithic application," Carsten notes. By breaking applications into smaller, independently scalable services, companies can optimise resource allocation for each component rather than scaling entire applications to meet peak demands."
"A small service is easier to scale than a monolithic application"
"The most efficient computational operation is the one that can be avoided," Carsten explains, highlighting caching as a powerful optimisation technique. While implementation can be complex, proper caching significantly reduces resource consumption while improving user experience through faster response times.
Data transfer reduction
"Data networks consume a lot of energy," says Carsten, "so it is crucial to reduce the amount of data in transit as much as possible." Strategies include optimising data formats, implementing compression, and avoiding unnecessary API calls.
Level 3: Code-level optimisation
The third level delves into application code itself, where significant efficiency gains can be achieved through careful optimisation.
Algorithm efficiency
Carsten emphasises the importance of selecting appropriate algorithms: "The 'Big O Notation' describes how an algorithm's runtime or space requirements grow as the input data size increases. This enables developers to choose the most efficient algorithm for a specific use case."
Database optimisation
"There often lies a vast potential for performance improvements on the code level," Carsten notes, particularly regarding database interactions. He recommends:
- Logging and analysing slow queries
- Using the EXPLAIN statement to optimise query execution
- Implementing appropriate table indexes
- Being cautious with abstraction layers like ORMs that can hide inefficiencies
Code profiling and clean-up
"Profiling will help you identify long-running functions within your code," Carsten explains. Regular code clean-up is equally important: "Legacy code should be removed as soon as it becomes outdated. Less code means better performance in general, but you also save time in the CI/CD pipeline due to fewer tests and faster code quality checks."
Level 4: Carbon awareness
Carbon awareness emerges as a pivotal concept.
"The concept of 'Carbon-Aware Computing' is still very young and rapidly evolving."
Carbon awareness targets the variability in electricity carbon intensity—the emissions generated per unit of electricity—which fluctuates based on the energy sources supplying the grid at any given moment. "The basic idea of 'Carbon Awareness' is to use green energy when available and reduce the demand when the carbon intensity is high," Carsten explains. He outlines several approaches:
Temporal shifting
Postponing non-urgent workloads to times when electricity is generated from cleaner sources, using forecasting services that predict carbon intensity up to 12 hours in advance.
Spatial shifting
Running computationally intensive workloads in regions with cleaner electricity grids, though Carsten cautions this approach comes with tradeoffs: "If everyone ran their software in the greenest region, it would soon overshoot the capacities there, so it is no holistic solution."
Demand shaping
Modifying application behaviour based on current carbon intensity: "Companies that stream data, like video or audio, could, for example, reduce the default quality with which the content is delivered when the carbon intensity is high."
Level 5: Product design
The final level transcends pure technology to embrace sustainable product and user experience design.
"We can't hope to fight climate change through the use of technology alone. It is necessary to change how we use products, too," Carsten points out.
Key principles include:
User awareness and choice
"Measures like reducing the video streaming bitrate should not be taken without informing the users," Carsten advises. He recommends not only informing users about sustainability features but actively engaging them: "Your customers should be able to actively opt-in (or opt-out) to carbon-saving measures."
Sustainable design patterns
Reconsidering fundamental assumptions about how products should function can yield significant sustainability benefits. "Does the data dashboard always need to be up to date and require constant database queries? Or would the user be okay with data that can be a couple of minutes old but allows the backend to cache requests and thus save resources?" Carsten asks.
Implementing a sustainable software strategy
Implementing green IT principles requires a structured approach. Carsten stresses that organising jobs to be done is essential to keep the strategy together.:
- Secure management buy-in for sustainability initiatives
- Analyse emissions and cost data to identify high-impact areas
- Formulate specific goals with measurable outcomes
- Develop a project plan with clear KPIs
- Track progress using metrics like weekly carbon emissions and infrastructure costs
- Calculate ROI to demonstrate business value
Most importantly, IT sustainability is an ongoing journey, not a one-time project: "Once the first carbon savings have been achieved, it is crucial not to stop but to keep the momentum going. As the typical IT landscape is ever-changing, constant monitoring and analysis are required."
Carsten's comprehensive five-level framework helps organisations transform their IT operations from emissions contributors to sustainability assets. Starting with infrastructure optimisation and progressing through increasingly sophisticated interventions, companies can achieve significant emissions reductions while potentially improving performance and reducing costs.
"Green IT is no one-off project but a shift in mindset and operations," Carsten concludes. This mindset shift represents perhaps the most crucial aspect of sustainable software engineering—recognising that technical decisions have environmental consequences and that those consequences can be systematically reduced through thoughtful design and implementation.
For companies looking to begin their IT decarbonisation journey, Plan A offers a comprehensive carbon management platform that can help measure and reduce emissions across your entire operation, including digital infrastructure. With expertise in carbon accounting, target setting, and decarbonisation strategies, Plan A's sustainability experts can help you develop a tailored approach to greening your IT operations.
Book a demo today to learn how Plan A can support your company's sustainability journey.
