Planetary health

Environmental sustainability assessment

In Life Cycle Assessment (LCA) we have a robust and standardised way of measuring environmental impact. However, this is not the same as sustainability. A comparative LCA assessment can tell you in what regards one product has less impact than another. It does not mean either product is sustainable, just one is superior to the other in a relative sense. To address this limitation, recent research has begun to develop tools to assess environmental sustainability in an absolute sense, meaning a definitive, numerical value describing an impact as sustainable or not. This has become known as 'absolute environmental sustainability analysis'. Just like LCA, it can be applied to individual products, organisations, or activities across entire regions. Unlike LCA, the indicator values are percentages. Values below 100% are considered sustainable, values above 100% are unsustainable.

Absolute sustainability

The format of an absolute sustainability indicator for a product is shown below in comparison to the usual LCA mid-point indicator. Both variables, impact and the functional unit, are normalised by additional terms (Sherwood, 2022). To do so, a portion of the global Safe Operating Space (SOS) has to be reserved for the production, use, and disposal of the product. Also, demand for the product is accounted for to normalise the functional unit. All the units cancel out and so absolute sustainability indicators are unitless. As with LCA, consistency is important so all the variables must relate to one another in scope. Unlike LCA, absolute sustainability is a reasonably new discipline and so different approaches are being used concurrently without a definitive consensus (Ryberg et al., 2020).

Paracetamol case study

We can apply absolute sustainability to pharmaceuticals by slightly adapting LCA studies. To take the example of paracetamol (acetaminophen), the reported climate change impact of 1 g of Active Pharmaceutical ingredient (API) is about 48 g CO2-eq. per gram once formulated and packaged (Piffoux et al., 2024). If the functional unit of an LCA study was 1 g of API, this could be a mid-point indicator for climate change. However, more context and comparability is gained by using a medicinal rather than a mass functional unit, namely defined daily dose (DDD). The DDD is 3 g for paracetamol (NIPH, 2024). Thus the impact is better described as 145 g CO2-eq. per DDD. The study by Piffoux et al. (2024)  is based in France in 2022 and so the calculated impact is relevant to this region (as it includes transport distances and specific energy mixes etc.). Therefore we shall downscale the climate change SOS to represent the provision of analgesics in France. Accordingly, the demand category shall apply to French analgesics. The climate change Planetary Boundary is 350 ppm of CO2 but we need units of mass per year to match to the impact data. There is a lot of conjecture over how much carbon dioxide emissions constitute an atmospheric concentration of 350 ppm. It depends on various factors described by the carbon cycle and it changes depending on the extent of carbon capture (natural and artificial). Here, we have used a value of 52 gigatonnes per year (Heide et al., 2023). This is downscaled to a value for France based on its population (0.85% of the global population), and again to match its analgesic market (0.02% of France's GDP). This leaves a value of 106 million kg CO2-eq. as the target emissions attributed to French analgesics. The downscaling methodology is somewhat contentious and different approaches have been developed (Ryberg et al., 2020). Finally, demand is 0.093 DDD per person per day in France (Hider-Mlynarz et al., 2018), which equates to 2.3 billion DDD per year. Once the variables are used in the absolute sustainability equation, the result is 317%.

The calculated absolute climate change sustainability of paracetamol, at 317%, is unsustainable, over triple the impact needed to be sustainable (which is 100%). But now we have a quantitative value, actions to reduce carbon emissions can be evaluated with a strong sustainability context. To reach a sustainable carbon footprint of 42 g CO2-eq. per DDD is challenging and will need a combination of efforts, be it targeted at the optimisation of paracetamol production, or alternative lower impact APIs. It is also clear from the absolute sustainability calculation that other interventions can help us reach an environmentally sustainable outcome. For example, if demand for medicine is decreased by a healthier population, or the share of the SOS is increased by reallocating from less important sectors, the indicator value will decrease. However, current practice is actually attributing more of the SOS to agriculture and food production (Springmann et al., 2018; Goss and Sherwood, 2024), and less to other sectors, even healthcare.

Limitations and outlook

Although the term 'absolute sustainability' could imply it is objective and infallible, there are many unresolved issues that must be appreciated during the interpretation of results. Firstly, despite the name, it remains subjective. The process of downscaling the Planetary Boundaries has several options leading to different results. Then the scope is not always 'cradle-to-grave'. This example is actually 'cradle-to-gate'. There is also the issue that the monetary value of products is usually the basis of allocating a share of the SOS. This is biased to more expensive articles, and depending on how the assessment is conducted, could favour branded products over generic medicines. It is also important to remember that only environmental sustainability is being explicitly described (although the demand variable does touch on social needs) and only impacts with a corresponding planetary boundary are applicable.

Despite absolute sustainability being a new and emerging methodology, it has been readily adopted in various formats and applied to many types of products and processes. Before it can be accepted on a par with LCA, or even supersede LCA, it will need to undergo a process of standardisation which will take several years. But assuming that can be achieved, a richer understanding of sustainability and sustainable actions becomes possible.