Carbon Efficiency

Last updated on 2025-05-01 | Edit this page

Overview

Questions

  • What does the term carbon equivalence (CO2e) mean?
  • Can we also have positive emissions impacts from HPC systems?

Objectives

  • Understand what CO2e means.
  • Appreciate positive emissions impacts from HPC systems.

Carbon and CO2e

Carbon is often used as a broad term to refer to the impact of all types of emissions and activities on global warming. CO2e (sometimes: CO2eq/CO2-eq), which stands for carbon equivalence, is a measurement term used to measure this impact. For example, 1 ton of methane has the same warming effect as about 84 tons of CO2 over 20 years, so we normalise it to 84 tons CO2e. We may shorten even further to just carbon, which is a term often used to refer to all GHGs.

Carbon efficiency in HPC system use

In the HPC space, the part we play in the climate solution is using HPC systems in a carbon efficient way. Being carbon efficient is about making sure your use of HPC systems emits the least carbon possible for the work you are doing. Or, for providers of HPC systems, it means procuring and operating the system in such a way as to minimise the carbon emissions. Ideally, you would also be able to quantify the positive carbon impacts from the work (or HPC system itself) to understand the overall net impact on carbon emissions - though doing this is typically quite challenging.

Exercise: Carbon emissions from HPC systems

What do you think the sources of carbon emissions may be from HPC system use? Write down 2-3 ideas of where you think emissions may come from.

You may have come up with sources such as:

  • Emissions from electricity generation to power the HPC system
  • Embodied emissions from manufacturing the HPC system components such as processors, memory and storage
  • Embodied emissions from constructing the data centre and other infrastructure to house the HPC system
  • Emissions associated with the people working to procure, run and support the HPC system

Exercise: Positive emissions impacts

Write down the outcomes or activities that you do as part of your research or work that could be produce positive carbon emissions. Once you have them written down, can you rank them in order of what you think the largest source of emissions will be to the smallest? Can you think of any way in which you might go about quantifying this positive impact so it could be included in a carbon audit of your work?

You may have come up with outcomes such as:

  • The research or work you are engaged in is developing new innovations and technologies to reduce or eliminate emissions
  • The research or work you are engaged in is providing data that is critical to efforts to quantify climate change and/or net zero strategies
  • You are involved in training, education and/or activities raising awareness of carbon emissions and helping others to reduce their emissions
  • You are developing resources and tools that help others to quantify and reduce their emissions

Quantifying positive emissions impacts are often even more difficult than quantifying the emissions we produce through our work but are critical to understanding how we are helping to meet climate commitments (which we will discuss later in this workshop).

For example, attending this workshop may empower you to go away and take some action to reduce the emissions associated with your work. Maybe each person who takes action following this workshop reduces their overall emissions by 2% this year but only 50% of people who come on the workshop manage to have this impact. This means that overall, we would see a 1% reduction in emissions for this year per person attending the workshop. If we assume that the work emissions per person per year are around 6,000 kgCO2e then this workshop would be estimated to save 60 kgCO2e per person attending the workshop.

Positive emissions impacts

As well as reducing emissions from our use of HPC systems there are typically other sources of positive carbon emissions impact associated with HPC

The main source of reduced emissions from HPC system use is in the research that leads to new technology, policies and approaches to reducing emissions. Some examples include:

  • HPC services run the climate models that are used to provide evidence for setting emissions reductions policies and targets across the world. Research and modelling on HPC services leads to development of improved zero emission energy generation by, for example, modelling new wind turbine and wind farm designs.
  • Modelling to support the development of new energy storage technologies such as improved batteries.

The emissions reductions from such activities are extremely difficult to quantify for a number of reasons so, at the moment, these are not factored in to the emissions estimates for HPC systems and research more broadly but you should be aware of them and think about how they might apply to your research in particular.

As well as the research activities on HPC systems leading to reductions in emissions, there are other activities that HPC services can potentially take to have positive emissions impacts, for example:

  • Using the waste heat generated by large scale HPC services as a heat source for homes, businesses or farming. For example, the LUMI HPC system in Finland is connected to the district heat network for the local city of Kaajani and helps heat homes and businesses.
  • Incorporating environmental and biodiversity improvements into the service. For example, for the ACF data centre that hosts ARCHER2 (which is in a rural location) EPCC have been working to improve the site biodiversity and improve habitats.
  • Responsible carbon offset schemes could also potentially be used to reduce emissions if they are undertaken as part of providing an HPC service.

Key Points

  • CO2e is a measurement term used to measure the impact of all greenhouse gases.
  • Some activities we undertake on HPC systems can potentially have positive carbon impacts but these can be very difficult to quantify.
  • Everything we do emits carbon into the atmosphere, and our goal is to emit the least amount of carbon possible. This constitutes the first principle of green HPC system use: carbon efficiency, emitting the least amount of carbon possible per unit of work.