Fertilisers hike your loaf’s carbon emissions Chris Ratcliffe/Bloomberg via Getty

Giving you your daily bread is costly for the climate. The equivalent of half a kilogram of carbon dioxide goes into the atmosphere for every loaf of bread produced in the UK, according to the best study on the subject yet.

That suggests making the bread eaten in the UK results in massive greenhouse emissions: equal to an astonishing half a per cent of all the UK’s greenhouse emissions. The finding highlights the urgent need to tackle global emissions from farming, which produces a third of all greenhouse gases.

In the case of a loaf of bread, the main source of these emissions is the nitrogen fertiliser used to grow the wheat. Its production and use creates 40 per cent of the emissions.


“The 40 per cent figure was quite a shock to us,” says Liam Goucher of Sheffield University in the UK, whose team worked with farmers and an industrial bakery to directly measure what goes into producing a wholemeal loaf.

While several other teams have calculated the emissions associated with bread-making, these studies relied more heavily on estimates than direct measurements.

Two-thirds of fertiliser emissions come from its manufacture, a high-temperature process that usually relies on natural gas.

Needs more dough

It can be made by using renewable energy to produce hydrogen from water instead – the very first industrial fertiliser was created this way. But as it is currently much more expensive to make fertiliser using this method, there is no financial incentive to switch to it.

The other third of fertiliser emissions are due to nitrous oxide. A little of the nitrogen in fertiliser gets converted into this highly potent greenhouse gas and released into the air after it is applied to soil.

Nitrous oxide emissions could be reduced by up to 30 per cent by measures such as applying fertilisers more efficiently, says Roger Sylvester-Bradley of agricultural research company ADAS, who studies such emissions. But again, some of these measures, such as adding emissions-reducing inhibitors to fertilisers, are more expensive.

Even switching to organic farming might not help. For instance, if farmers grow nitrogen-capturing legumes and spread them on fields as a “green fertiliser”, nitrous oxide is still released, says Sylvester-Bradley.

Ploughing soils that are rich in organic matter also releases lots of carbon, he says. Other studies have found that growing organic wheat results in similar amounts of greenhouse gas emissions to conventional wheat farming, or even slightly more.

Organic farms also use far more land per loaf produced: land that could instead be set aside for wildlife or used for biomass energy.

Journal reference: Nature Plants, DOI: 10.1038/nplants.2017.12

Read more: Britons may have imported wheat long before farming it