What is carbon intensity?

Why it matters

A kWh from a grid running mostly on coal or gas carries far more emissions than one from a grid running mostly on wind, hydro or nuclear. The generation mix changes through the day and differs between areas, so carbon intensity varies by region and by hour. The same workload can have a very different footprint depending on where and when it runs.

For cloud users, that makes region and timing two of the main levers on emissions. Moving flexible work to a cleaner region or hour can reduce location-based emissions with no change to the code. Savings worked out this way are average-basis figures, because the factors describe the average mix and not the plants that respond to a change in demand.

An example

In the US, Greenpixie resolves each cloud region to the county or counties it occupies and weights the balancing authorities serving them, a narrower basis than a state or national average. In the UK, cloud regions in London, Cardiff and the North West of England each carry their own hourly figure, because each draws on a different distribution region's generation mix.

How Greenpixie measures it

GPX Grid produces hourly carbon intensity for 269 cloud regions across AWS, Azure and Google Cloud, built from 91 grid areas. Each total is the sum of three parts:

• combustion at the power station, which a location-based reporter counts as Scope 2
• upstream and downstream emissions from the rest of the fuel life cycle, counted as Scope 3
• transmission and distribution losses, counted as Scope 3 Category 3

For each grid area, Greenpixie multiplies each fuel's share of the hour's generation by that fuel's emission factor and adds the results. Each cloud region then takes the weighted average of the grid areas that supply it.