For many years, the recycling rate has been seen as the most important gauge of environmental performance when it comes to waste management, and it is the recycling league table that councils aspire to top. As a metric, recycling has advantages: it’s easy to understand, easy to calculate and relies on known data.

However, there are problems using just this measure. For starters, it does not capture the relative value of collecting different materials. Recycling a tonne of paper brings significant environmental benefits, but recycling a tonne of aluminium is many times more beneficial.

Focusing on recycling rates also overlooks the benefits of working at the top of the waste hierarchy on prevention activities, and fails to say anything about the relative environmental impact of different approaches to residual waste treatment (more about these later.)

Scotland has taken an important step in moving beyond recycling rates by adopting the more informative ‘carbon metric’. Using this approach, Scottish councils now report not just on the weight of the recyclate that they collect, but also on the positive environmental impacts of the services they provide in terms of avoided carbon (or carbon equivalents). Although the approach hasn’t been perfect – Zero Waste Scotland is now on its fourth definition of a ‘carbon metric’ – it is ambitious and to be credited for leading the way.

For some time, there has been a need to develop and apply a more sophisticated metric, which looks at the whole carbon impact of local authorities’ waste and collection services in other parts of the UK. Eunomia’s new Local Authority Recycling Carbon Index is our first attempt. Based on WasteDataFlow reporting, this simply quantifies the carbon benefit of the recycling that an authority does.

The tables on the page opposite show how both waste disposal and unitary authorities did in 2011/12 (more detailed findings and analysis can be found in the full report). To help put perspective on the difference between the top and bottom performers in the index, if every local authority in the UK were to match the best, North Somerset, then the carbon saved through recycling would be the equivalent of taking 2.2 million cars off the road. Conversely, if all councils matched the worst performers, then it would only be the equivalent of taking 400,000 cars off the road (compared to not recycling at all).

While we caution against drawing too many conclusions on the back of the first table of this kind, there are some characteristics that help an authority achieve a good score on this metric. These include: separately collecting food waste and sending it for anaerobic digestion; sending source-segregated dry recyclables to closed-loop recycling; squeezing residual to make recycling the default; achieving high levels of separation at household waste recycling centres; and focusing on key materials such as metals, textiles and plastic.

This analysis is just a starting point, and inevitably there are limitations, but a journey of a thousand low-carbon miles begins with the first step. Here, the benefit identified encompasses the reduced need to extract and process raw materials into finished products – also known as the embodied carbon of each material.

In the future, our plan is to account for the carbon savings of waste prevention and carbon intensity of residual waste treatment.

However, the ultimate goal has to be a metric that captures the environmental value of avoided waste, which accounts for the carbon impacts of a product through its whole lifecycle. This approach is fraught with difficulty, as it requires compositional data for the waste stream of each local authority – something not openly available. A blanket approach using national compositional data fails to account for geo-demographic variation. For instance, inner cities do well because the lack of gardens means less garden waste.

On this occasion, because of difficulties with the data, we’ve kept it simple. We hope that it provides some value to authorities thinking about the environmental performance of their recycling services and how they can improve these.

Simon Hann is a Life Cycle Assessment Specialist at Eunomia.

Read Eunomia's 'Recycling Carbon Index'.