When discussing Embodied Carbon, amortisation refers to dividing the total embodied carbon of a device by its expected lifespan. This gives a way of accounting for the emissions of a device on a yearly basis. For example: a 2023 Apple 16” Macbook Pro has an embodied carbon of 290kg CO2e so with a life cycle of four years, that gives an amortisation of:

$$ Amortisation = \frac{290\ kg\ CO2e}{4\ years} = 72.5\ kg\ CO2e/year $$

Extending the life of a device, i.e. using it beyond its expected life cycle, can have a significant impact on the amortised emissions. If that Macbook’s life cycle was extended to 6 years before being scrapped (and ideally recycled), the amortisation can be re-calculated as:

$$ Amortisation = \frac{290\ kg\ CO2e}{6\ years} = 48.3\ kg\ CO2e/year $$

Therefore, a saving of over 24kg CO2e per year is possible by extending the life of the MacBook to six years.

Carbon Awareness

An emerging sustainable design principle for software. Because carbon intensity fluctuates with time and region you can design software that measures and/or predicts when and where the electricity grid is cleanest and can schedule time-insensitive tasks to run during these periods. Think of overnight backups, batch sending of newsletters or training of ML models. These can be delayed a few hours and not harm or delay the delivery or promotion of new products.

Carbon Dioxide Equivalent (CO2e)

As a way of quantifying the effect of all GHG emissions emitted CO2 is used as the baseline. Some GHGs are more potent and others are less. For example R-410A, one of the most common refrigerants used in AC units, is 2,088 more potent than CO2 therefore a leak of 1 kg of R22 is the same as a 2 tonne leak of CO2.

Carbon Intensity

The amount of carbon emitted per unit of electrical energy of a country/region’s grid. This varies not only with geographical location but also with time as it depends on the proportion of renewable energy sources which have highly variable output depending on the wind/waves/sun/rainfall at any point in time. There are two methodologies for calculating this:

Location Based

This method only considers the carbon intensity of the local grid and ignores the electricity mix purchased from suppliers. These figures can be obtained from Ember Data Explorer; some examples are shown below:

Region Carbon Intensity (gCO2e/kWh)
Global 490
Europe 328
Asia 591
France 56
Germany 381
UK 238
USA 410
China 586

Figures for France, Germany, and the UK are based on 2023 data. Other locations are based on 2022 data. Source: Ember Data Explorer

There are other sources of credible data including government and government-affiliated sources (energy ministries, statistical bureaus) and utility companies that generate or manage power directly. For example, the IEA (International Energy Agency) providers emissions factors products. There are also online platforms such as Electricity Maps which provide visualisations of carbon intensity data parsed from reputable data sources.

Market Based

This method considers the electricity you have purchased from your suppliers which could be green energy tariffs that leverage Renewable Energy Certificates (RECs) and Guarantees of Origin (REGO) allowing benefits in reporting for companies that source their electricity more sustainably.

Carbon Neutral

Negating the carbon emissions of your direct and indirect emissions. This is done by either reducing or offsetting your current carbon emissions. Reducing should be the first action you take and then any sources of emissions that are unavoidable can be offset using schemes that absorb CO2. These schemes include reforestation and solar energy installations.

Carbon Offsetting

Carbon offsetting aims to counterbalance carbon emissions to achieve neutrality, but does not eliminate the original emissions. It is a controversial approach but widely used by those looking to reduce their climate impact.

Climate Change

The long term change in average weather patterns which is part of the natural life cycle of the Earth and is being accelerated by human related activities like burning fossil fuels.

Data Center infrastructure Efficiency (DCiE)

It is really just the reciprocal of the PUE that can give the value as a percentage (if multiplied by 100), it can be used to simplify equations for determining the total energy used by your software.

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Embodied Carbon

The emissions associated with the manufacture, transportation, installation, maintenance, and end-of-life of a device or product.

Embodied carbon emissions often contribute a larger portion of the total emissions in the technology industry compared to other sectors. These emissions are more challenging to quantify as they are indirect and typically require businesses to interact with suppliers and retrieve emissions data for the purchased products, such as Product Carbon Footprint (PCF) data. Although the availability of such data is becoming more widespread, there is currently no standardised way to access this information for all products.

Read more about embodied carbon emissions.

Energy Efficiency

The efficiency of software with respect to how much energy it consumes, the higher the energy efficiency, the less electricity consumed. If the system is run on fossil fuel derived electricity then the higher the efficiency, the less emissions emitted by the software. It can be seen as the operational efficiency of software.

Fossil Fuel

A natural fuel that is formed by the remains of animals or plants that lived in the past. This fuel is not quickly produced, much slower than the rate of extraction, and the burning of them results in the re-emission of carbon that was stored within the remains of the organisms leading to GHG accumulation in the atmosphere. These two points make this type of fuel non-renewable and unsustainable. Examples include coal, oil and gas.

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Greenhouse Effect

The warming effect due to greenhouse gases. This happens because incoming shortwave radiation from the Sun passes through GHGs but the longwave radiation that is emitted by the heated Earth is absorbed by GHGs insulating the Earth from heat loss to space. The net effect is the slow warming of the atmosphere as the concentration of GHGs increases.

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Greenhouse Gas (GHG) Protocols

Greenhouse Gas protocols set the standard to measure and manage emissions.

Scope 1

Includes all direct emissions that are generated from sources that are directly owned or controlled by an organisation. For a software company there is a very small list of sources but it is not empty. It can include any emissions from fossil fueled hire cars used to visit customers and emissions from refrigerant leaks found in A/C & fuel burnt in heating systems within offices.

Scope 2

Includes all indirect emissions from the generation of the electricity purchased and used by an organisation at local or international sites. This is a much larger list for a software company. The most prominent is the electricity produced to run computers, office lights and office A/C and heating systems.

Scope 3

Includes all indirect emissions that occur in an organisation’s value chain. The largest and hardest to quantify because it relies on suppliers to provide detailed breakdowns of a product’s carbon footprint. This scope includes areas like emissions from cloud infrastructure and the embodied carbon of computer hardware.

GHG Protocols

Green Energy

A source of energy that does not harm the environment during it’s operation. However, the production, transport and end of life process will typically emit carbon emissions and cause other harmful effects. Examples inlcude solar, wind, and nuclear energy.

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Green Software

This term can have two meanings. The first and most used is for software that is designed to help the environment. So an app that is aimed at reducing food waste would be classed as green software. There is also another meaning that can be derived from the definition of ‘Green Energy’ which is a piece of software that has not harmed the environment during its development and operation.

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Greenhouse Gases (GHGs)

These are gases that amplify the greenhouse effect, the effect caused by trapping energy from the sun within the Earth’s atmosphere. Examples are the well known Carbon Dioxide (CO2) emitted from electricity generation and other lesser known gases like Methane (CH4) sourced from office catering production and disposal and hydrochlorofluorocarbons (HCFCs) used in office cooling systems.

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Is the act of marketing or presenting an organisation as beneficial to the environment, however, actually hiding the truth. This can be done by making unsubstantiated environmental claims, hiding or downplaying the most heinous environmental acts or even just overselling the environmental gains to aid in consumer buy-in.

Hardware Efficiency

The efficiency of software with respect to how much hardware is required for it to be operational. The higher the hardware efficiency, the less emissions emitted to manufacture and transport the required hardware. It can be seen as the embodied efficiency of software.

Kilowatt Hour (kWh)

A standardised unit of measurement for energy that many cloud service providers and carbon emission calculating tools use. It equates to a 1kW device running for 1 hour, which is the equivalent to 3,600,000 Joules.

Life Cycle Assessment (LCA)

A method used to evaluate the environmental impacts of a product or system by looking at its entire product life cycle, considering a variety of environmental impacts such as climate change, water consumption, land use, and health factors.

An LCA considers a broad range of environmental impacts of a product. This is different to Product Carbon Footprint (PCF) which assesses only the climate impact (environmental impacts due to GHG emissions).

Read more about life cycle emissions data.

Marginal Carbon Intensity

The carbon intensity of the extra electricity that was produced to meet the change in demand due to the load of a piece of software. It is a way of analysing the optimal time and location of carbon aware applications. Within a grid’s energy sources, there is a base load of fossil fuel or nuclear energy and a mix of fluctuating renewable sources. It is widely seen that to meet an increase in demand there are two methods, pausing the curtailment of sustainable energy sources or increasing the base load of a fossil fuel source.

Net Zero

A standard designed by The Science Based Targets initiative (SBTi) which takes carbon neutrality to the next level by ensuring businesses reduce their emission by 90% by only allowing them to offset a maximum of 10% of their emissions. It can be applied to CO2 only or to all GHGs.

Paris Agreement

A legally binding international treaty on climate change with the goal of preventing “the increase in the global average temperature to well below 2°C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels”.

Power Profiling

Power profiling is the process of measuring and recording the power use of a device, or specifically compute processing.

For more information about power profiling, with an emphasis on Intel processors used in desktop and laptop machines; read more

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Power Purchase Agreements (PPA)

A long-term contract for the sale of electricity generated from renewable energy sources like solar, wind, or hydropower. PPAs provide the developer with a guaranteed revenue stream to finance projects, and allow the purchaser to secure renewable energy at a fixed price for many years. This also provides the purchaser with RECs that cover the energy purchased.

PPAs are critical for financing new renewable energy projects and encourage additionality in terms of increasing the renewable energy provided to the grid. The purchaser will likely still receive power from the grid or at least rely on it during periods where renewable sources are limited.

Power Usage Effectiveness (PUE)

A factor that describes how efficient a data centre is, it is the electrical energy fed into the computer hardware over the total energy drawn from the grid. Sources of inefficiencies can come from lighting, cooling and even the kettle in the staff kitchen.

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Product Carbon Footprint (PCF)

A method used to assess the climate impact of a product through the measurement of the greenhouse gases (GHGs) emitted throughout its product life cycle. GHGs are translated into carbon equivalents (CO2e) for comparison purposes.

The evaluation of a product’s carbon footprint typically involves conducting a Life Cycle Assessment (LCA) to assess the environmental impacts associated with all stages of the product’s life. The difference is that a full LCA looks at wider environmental impacts (such as land use, water consumption) whereas PCF focuses on the environmental impacts due to GHG emissions.

Read more about life cycle emissions data.

Product Life Cycle

Refers to all of the aspects that contribute to the environmental impact of a device. This includes:

Aspects like usage will need to take into account the expected life span of the device, its typical use patterns, and the carbon intensity of the energy used to power the device.

The environmental impacts of a product or device throughout its product life cycle can be assessed by considering its Life Cycle Assessment (LCA) or Product Carbon Footprint (PCF).

Read more about life cycle emissions data.

Running Average Power Limit (RAPL)

Intel (Sandy Bridge and later) processors that implement the RAPL (Running Average Power Limit) interface provides model-specific registers (MSRs) containing energy consumption estimates for up to four power planes or domains of a machine.

For more information on RAPL tools; read more

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Renewable Energy

A source of energy derived from natural sources whose reserves are replenished at a higher rate than its consumption. Examples of renewable energy are wind, solar and geothermal. This does not mean that they are sustainable, if we extracted oil at a slower rate than their reserves were replenished it would count as a renewable energy source even if the CO2 emissions are accelerating climate change.

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Renewable Energy Certificates (RECs)

A tradeable certificate representing the environmental benefits of 1 megawatt-hour of renewable electricity generation. RECs are sold separately from the underlying electricity, which is still provided by the grid. RECs provide a revenue stream for renewable energy projects and allow organizations to meet their renewable energy targets.

Software Carbon Intensity (SCI)

A methodology developed by the Green Software Foundation to help calculate and track the impact of software, it is designed to be widely applicable and calculatable with a bias towards actions that eliminate carbon emissions. It considers both usage and embodied carbon and has a scaling factor (R) that allows for a value that is independent of the size of the system which could be for example per transaction or per user. The inclusion of embodied carbon ensures that this value can never reach zero but gives a value that can be tracked to validate improvements over time.

Sustainable Energy

A source of energy that can be relied upon for an extended period of time. To ensure an energy source is sustainable many different factors must be taken into account, from possible negative impacts on the natural world (biodiversity loss due to forest clearing for biomass production) to negative health impacts on humans (air pollution from burning fossil fuels).

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Sustainable Software

Software that can continue operating for a prolonged period of time without harmful effects on the environment and society. Possible sources of harm for software are air quality, biodiversity, human poverty and equality.

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Typical Energy Consumption (TEC)

A method of comparing the energy performance of devices. TEC refers to the typical or average amount of energy consumed by a device while performing a typical workload over a certain time period (i.e. the energy consumption associated with standard household usage). It is expressed in units of kWh per year. Amongst similar devices, a lower TEC usually indicates more efficient energy usage. It is based on standard assumptions about the time spent in different usage modes (off, idle, max) and gives a more real-world metric compared to peak power ratings.

TEC is often used in Energy Star specifications and efficiency standards for servers, storage devices, networking equipment, and other data centre hardware. Manufacturers may be required to publicly disclose TEC ratings to sell certain products.

Usage Carbon

Carbon emissions from the usage stage of the product life cycle. This refers to the greenhouse gas (GHG) emissions associated with the operation and use of a device or product throughout its entire life cycle, including the energy required to keep servers and devices running, and to transfer data from servers to the devices.

Factors influencing usage carbon include the device’s energy efficiency, usage patterns, life span, and the carbon intensity of the energy grid powering it.

Read more about usage carbon emissions.

Waste Electrical and Electronic Equipment (WEEE)

Waste Electrical and Electronic Equipment (WEEE) refers to discarded electronic devices that have reached end-of-life (EOL). This includes used electronics destined for reuse, resale, recycling, or disposal.

The proliferation of electronic goods and short innovation cycles has led to a global e-waste problem. Electronic scrap components, such as CPUs, contain potentially harmful materials such as lead, cadmium, beryllium, or brominated flame retardants. Improper handling during recycling and disposal carries environmental and human health risks.

Rapid technological advancement and consumption continues to fuel rising e-waste volumes globally. The EU WEEE Directive is a policy effort aimed at regulating and mitigating this electronic waste stream through treatment, recovery, and responsible disposal requirements for certain electronic goods.