Introduction

  • Green software adheres to…

Carbon Efficiency

  • Emit the least amount of carbon possible.

Energy Efficiency

  • Electricity is a proxy for carbon, so building an application that is energy efficient is equivalent to building an application that is carbon efficient.
  • Green software takes responsibility for its electricity consumption and is designed to consume as little as possible.
  • Quantifying the energy consumption of an application is a step in the right direction to start thinking about how an application can operate more efficiently. However, understanding your application’s energy consumption is not the only story. The hardware your software is running on uses some of the electricity for operational overhead. This is called power usage efficiency (PUE) in the cloud space.
  • The concept of energy proportionality adds another layer of complexity since hardware becomes more efficient at turning electricity into useful operations the more it’s used.
  • Understanding this gives green software practitioners a better insight into how their application behaves with respect to energy consumption in the real world.

Carbon Awareness

  • Carbon awareness means understanding that the energy you consume does not always have the same impact in terms of carbon intensity.
  • Carbon intensity varies depending on the time and place it is consumed.
  • The nature of fossil fuels and renewable energy sources means that consuming energy when carbon intensity is low increases the demand for renewable energy sources and increases the percentage of renewable energy in the supply.
  • Demand shifting means moving your energy consumption to different locations or times of days where the carbon intensity is lower.
  • Demand shaping means adapting your energy consumption around carbon intensity variability in order to consume more in periods of low intensity and less in periods of high intensity.

Hardware Efficiency

  • Embodied carbon is the amount of carbon pollution emitted during the creation and disposal of a device.
  • When calculating your total carbon pollution, you must consider both that which is emitted when running the computer as well as the embodied carbon associated with its creation and disposal.
  • Extending the lifetime of a device has the effect of amortizing the carbon emitted so that its CO2eq/year is reduced.

Measurement

  • The GHG protocol is a metric for measuring an organization’s total carbon emissions and is used by organizations all over the world.
  • The GHG protocol puts carbon emissions into three scopes. Scope 3, also known as value chain emissions, refers to the emissions from organizations that supply others in a chain. In this way, one organization’s scope 1 and 2 will sum up into another organization’s scope 3.
  • Calculating software-driven emissions using the GHG protocol is possible but can be difficult for open-source software.
  • The SCI is a metric designed specifically to calculate software emissions and is a rate rather than a total.
  • The functional unit of measurement is not prescribed in the SCI and you should choose something that reflects your application.

Climate Commitments

  • There are a number of methodologies commonly applied to help in the overall fight against climate change. These fall into the general categories of carbon elimination (also known as ‘abatement’), carbon avoidance (a.k.a. ‘compensating’), or carbon removal (a.k.a. ‘neutralizing’).
  • Abatement includes increasing energy efficiency to eliminate some of the emissions associated with energy generation. Abatement is the most effective way to fight climate change although complete carbon elimination is not possible.
  • Compensating includes the adoption of renewable energy sources, sustainable living practices, recycling, planting trees etc.
  • Neutralizations refer to the removal and permanent storage of atmospheric carbon to counterbalance the effect of releasing CO2 into the atmosphere. Neutralizations tend to remove the carbon from the atmosphere in the short and medium-term.
  • An organization can call itself Carbon Neutral when its total emissions are matched by the total of its emissions offsets through carbon reduction projects
  • Net zero aims to eliminate emissions and only offset the residual emissions that you cannot eliminate to reach the 1.5°C target set by the Paris Climate Agreement.
  • The SCI is carefully designed so that eliminating emissions, through energy efficiency, hardware efficiency and carbon awareness is the only way to reduce the score. Together with a separate neutralization strategy, it can form the basis of a net-zero strategy for an organization.
  • When organizations set a target of 100% renewable power, they can either be “matched by” vs. “powered by” renewables, where “powered by” means the energy the device receives only originates from renewable sources. This can be achieved by purchasing RECs as part of a PPA.
  • 24/7 hourly matching is one of the many strategies we need to employ to help accelerate the transition to a 100% renewable-powered grid.