Diet shifts could reduce nitrogen pollution

Halving the consumption of meat, egg and dairy products only reduces protein intake by ten per cent. Photo: Lisa/ Flickr.com/cc by-nc-nd

Halving the consumption of meat, dairy and eggs in Europe could reduce ammonia and other nitrogen emissions by 40 per cent.

It is a long-known fact that animal husbandry causes emissions of nitrogen and greenhouse gases. Additionally the growing of feed for animals occupies vast land areas – land that has other potential uses. Another common piece of knowledge is that the average European eats far more meat and cheese than is recommended on health grounds. In particular, this leads to a high intake of saturated fats that cause cardiovascular diseases.

If EU citizens could halve their consumption of products from land animals, several targets could be achieved with one shot. Using a biophysical model, a new study has for the first time quantified the effects this would have for nitrogen, greenhouse gases, land use and health.

As meat consumption varies between member states, the reductions were made proportionally greater in member states with higher consumption than others.  Goat and sheep meat were kept at the same levels as today, since they have an important role in the management of biodiverse grasslands. Fish consumption was also maintained at present levels.

It was assumed that the reduced consumption would have a proportional effect on the number of livestock, which in turn affects the demand for feed. Another assumption made was that permanent grasslands and fodder by-products from the food industry would be used to the same extent as today. On the other hand, soymeal imports would be reduced by 75 per cent, forage grown on arable land would go down by 90 per cent and the use of cereal feed would drop by 52 per cent.  In areas this would mean that

9.2 million hectares of intensively managed grassland and 14.5 million hectares of arable land in the EU would be free for other use. In total, this is an area roughly the same size as Romania.

It is difficult to assess what would be the most likely alternative land use. In this study two rather schematic scenarios are investigated. In the first, cereals are grown on the entire area for export, assuming a high global demand. In the other, perennial energy crops are grown on the part that is arable land today.

Under the energy crop scenario, the use of mineral nitrogen fertilisers would be reduced by 30 per cent.  Emissions of nitrogen into the water, as nitrate (NO3-), and into the atmosphere, as ammonia (NH3), would drop by 40 per cent, reducing the area where critical loads for nitrogen in ecosystems are exceeded (figure). The reductions would be greatest in areas with the most intensive livestock systems.

Figure: Annual exceedance of the critical load for N deposition in N ha⁻¹ for natural ecosystems, under the reference scenario and the 50% less meat and dairy alternative diet under the high prices land-use scenario.

The level of nitrogen use efficiency¹ in the European food system would rise from today’s 22 per cent to 41 per cent under the energy crop scenario and to 47 per cent under the cereal scenario.

Greenhouse gas emissions from agriculture would meanwhile drop by 42 per cent under the energy crop scenario. The biomass produced is estimated to represent 3 per cent of the EU’s current energy intake and if all new biomass replaces fossil fuels it would mean even further reductions of greenhouse gases.

Under the cereal scenario, greenhouse gas emissions would fall by only 19 per cent. Nitrous oxide emissions would be reduced to a lesser extent and some grasslands would be tilled, which would reduce the carbon stock and lead to CO₂ emissions. 

Increasing the volumes of cereals on the world market as well as reducing the consumption of imported soya would most likely also lead to global net emission reductions. These are however not quantified in the study.

What effects would this have on health? Halving the intake of animal foods and replacing them with plant foods does not cause acute protein deficiency. It turns out that the protein intake at most is reduced by 10 per cent. In contrast the intake of saturated fats is reduced by 40 per cent, bringing average levels to slightly below the WHO recommendations of a maximum intake of 25.5 g per day. It would most certainly lead to a reduction in cardiovascular diseases and stroke, to which 40 per cent of all deaths in the region can be attributed today.  In addition there are several possible indirect health benefits through improved water quality (less nitrate), reduced levels of air pollution (less formation of PM from ammonia) and lower use of antibiotics.

The model used is a biophysical one. It does not take into account possible changes in trade that might occur if consumption patterns In Europe were to change rapidly. If European farmers maintained their production and exported the surplus to other continents, regional environmental improvements would be lost. The authors argue that this is not very likely since productions costs for most livestock products are lower in many non-EU countries, such as US, Brazil, China and Thailand.

However one should not overlook the obvious fact that halving the consumption of animal products would have severe consequences for the livestock sector. This would not be compensated for by an increase in incomes from plant products for direct human consumption. One possibility is that consumers might be more willing to buy animal products with a higher added value, e.g. produced under better animal welfare conditions.

One crucial question to ask is how to implement such a massive dietary shift.  The authors don’t provide a silver bullet, but identify the potential for encouraging new food habits through campaigns, active public procurement and taxation of animal products.

Higher world market prices could also reduce consumption in Europe, however without decreasing production, because exports would become more lucrative.

Kajsa Lindqvist

¹ Nitrogen use efficiency equals nitrogen outputs (in this case nitrogen in the food we eat) divided by nitrogen inputs (in this case nitrogen in imported feeds and mineral fertilisers).

Source: Food choices, health and environment: Effects of cutting Europe’s meat and dairy intake, published in Global Environmental Change (26 March 2014).