Reducing carbon emissions from fertilizers

University of Cambridge (WeatherFarm) – Researchers have calculated the carbon footprint for the full life cycle of fertilizers, which are responsible for approximately five per cent of total greenhouse gas emissions. This is the first time such has been accurately quantified and found that carbon emissions could be reduced to one-fifth of current levels by 2050.

The researchers, from the University of Cambridge, discovered that two-thirds of emissions from fertilizers take place after they are spread on fields, with one-third of emissions coming from production processes.

Although nitrogen-based fertilizers are already known to be a major source of greenhouse gas emissions, this is the first time their overall contribution – from production to deployment – has been fully quantified. Their analysis found that manure and synthetic fertilizers emit the equivalent of 2.6 gigatonnes of carbon per year – more than global aviation and shipping combined.

Carbon emissions from fertilizers urgently need to be reduced; however, this must be balanced against the need for global food security. Earlier research has estimated that 48 per cent of the global population are fed with crops grown with synthetic fertilizers, and the world’s population is expected to grow by 20 per cent until 2050.

The Cambridge researchers said a combination of scalable technological and policy solutions are needed to reduce fertilizer emissions while maintaining food security. However, they estimate that if such solutions could be implemented at scale, the emissions from manure and synthetic fertilizers could be reduced by as much as 80 per cent, to one-fifth of current levels, without a loss of productivity. Their results are reported in the journal Nature Food.

“Incredibly, we don’t actually know how many chemicals we produce globally, where they end up, where and how they accumulate, how many emissions they produce, and how much waste they generate,” said co-author Dr André Cabrera Serrenho from Cambridge’s Department of Engineering.

Serrenho and co-author Yunhu Gao undertook a project to accurately measure the total impacts of fertilizers, one of the two main products of the petrochemical industry. Of all the products made by the petrochemical industry, the vast majority – as much as 74 per cent – are either plastics or fertilisers.

“In order to reduce emissions, it’s important for us to identify and prioritise any interventions we can make to make fertilizers less harmful to the environment,” said Serrenho. “But if we’re going to do that, we first need to have a clear picture of the whole lifecycle of these products. It sounds obvious, but we actually know very little about these things.”

The researchers mapped the global flows of manure and synthetic fertilizers and their emissions for 2019, along all stages of the lifecycle, by reconciling the production and consumption of nitrogen fertilisers and regional emission factors across nine world regions.

After completing their analysis, the researchers found that unlike many other products, the majority of emissions for fertilizers occur not during production, but during their use.

“It was surprising that this was the major source of emissions,” said Serrenho. “But only after quantifying all emissions, at every point of the lifecycle, can we then start looking at different mitigation methods to reduce emissions without a loss of productivity.”