Researchers calculate environmental impact of a loaf of bread

Researchers have calculated that ammonium nitrate fertiliser accounts for 43% of the greenhouse gas emissions
Researchers have calculated that ammonium nitrate fertiliser accounts for 43% of the greenhouse gas emissions

Researchers have now calculated the environmental impact of a loaf of bread and which part of its production contributes the most greenhouse gas.

With an estimated 12 million loaves sold in the UK every day, bread remains a staple of the British diet.

Looking at the emissions associated with the wheat-to-bread supply chain and reporting their findings in the journal Nature, University of Sheffield researchers assessed “primary data for all the processes involved in the farming, production and transport systems that lead to the manufacture of a particular brand of 800g loaf.”

The study shows ammonium nitrate fertiliser used in wheat cultivation contributes almost half (43 per cent) of the greenhouse gas emissions – dwarfing all other processes in the supply chain.

They found that more than half of the emissions associated with industrial bread production occur at the wheat growing stage, highlighting the “Dependency of bread production on the unsustainable use of fertiliser.”

It is estimated that up to 60 per cent of agricultural crops are now grown with the use of fertilisers.

Although they can dramatically boast the growth of plants and vegetables – assisting the growing demand of food yields – fertilisers consist of substances and chemicals such as methane, carbon dioxide, ammonia and nitrogen.

Scientists say the emissions from these substances in synthetic fertilisers contribute to greenhouse gases.

'Consumers unaware'

Dr Liam Goucher, who carried out the study, said consumers are 'usually unaware' of the environmental impacts embodied in the products they purchase.

“Particularly in the case of food, where the main concerns are usually over health or animal welfare,” Dr Goucher explained.

“There is perhaps awareness of pollution caused by plastic packaging, but many people will be surprised at the wider environmental impacts revealed in this study.

“We found in every loaf there is embodied global warming resulting from the fertiliser applied to farmers’ fields to increase their wheat harvest. This arises from the large amount of energy needed to make the fertilizer and from nitrous oxide gas released when it is degraded in the soil.”

Professor Lenny Koh, a co-author on the report, said: “The findings raise a very important issue – whose responsibility is it to bring about the implementation of these interventions: the fertiliser manufacturer, the farmer, the retailer or the consumer?

“There is a growing recognition for a range of industrial processes of the notion of extended producer responsibility – the producer being responsible for downstream impact, expanded to the idea of shared producer and consumer responsibility.

“The consumer is key, whether being persuaded to pay more for a greener product or by applying pressure for a change in practice.”