The Sustainable Food Trust recently held an event to discuss the question ‘What role for grazing livestock in a world of climate change and diet-related disease?’
We feel this is one of the defining questions of our age because it’s really about what we should eat to stay healthy and how food should be produced in future so that we don’t ruin the planet for ourselves and for future generations. Current food production methods are causing huge problems and are unsustainable. We are over-using finite resources, polluting the atmosphere and the environment, destroying wildlife, including pollinators on which much food production actually depends and we are harming our health in the process.
We invited 50 scientists, policy-makers, campaigners and industry representatives to discuss these issues, but also filmed the presentations, which you can watch below, to make them widely available. We also plan to publish further details of the discussions and conclusions in due course.
Increasingly these days we are told to eat less meat, and less red meat in particular because cattle, sheep and other grazing animals emit the potent greenhouse gas methane and because red meat has been linked to a number of health problems including coronary heart disease, cancer and type-2 diabetes. In addition, population growth is predicted to increase demand for meat, while over-grazing (keeping more animals than grassland can comfortably feed) is a major cause of soil degradation – one of the most serious problems faced by humankind. Most of these issues are set out by Professor Pete Smith, who gave the opening presentation.
Open and closed case? Well not quite. Methane isn’t the only greenhouse gas associated with food production and there are also big questions about whether the negative health issues are associated with all red meat, only processed red meat, or only red meat from animals kept intensively and fed on grain. Let’s look at one of many issues explored during the day.
Chickens produce white meat, believed to be healthy, and they emit very little methane. But chickens require large amounts of grain and this puts them in direct competition for food with humans, while cattle and sheep can thrive eating nothing but grass, which we can’t eat.
Plants emit no methane, but they all need nitrogen to grow and almost all food is grown these days with nitrogen fertiliser, produced on an industrial scale from natural gas, which is mostly methane. But as Professor Bob Rees explains in his presentation, the production of nitrogen fertiliser on its own puts greenhouse gases into the atmosphere equivalent to about 8 tonnes of carbon dioxide for every tonne of nitrogen produced, and globally more than 100 million tonnes is used every year to produce food.
Nitrogen in food systems also leads to high emissions of the atmospheric pollutant ammonia and high levels of the greenhouse gas nitrous oxide, which in addition to its contribution to global warming is currently also the major cause of the hole in the ozone layer – a significant cause of skin cancer. Natural gas is also a finite resource and global reserves will only last for about another 50 years. This means that sooner or later we will have to find an alternative.
The only truly sustainable alternative is legumes – plants which naturally produce their own source of nitrogen, by turning nitrogen in the air into nitrate which plant roots can take up. But while peas and beans, which we can eat, ‘fix’ some nitrogen in this way, only a small proportion of land is suitable for their production. We couldn’t live on peas and beans alone, and only forage legumes like clover and lucerne (alfalfa) fix enough enough nitrogen to maintain current high crop yields. But forage legumes can only be utilised by grazing animals, and the nitrogen fertiliser used in crop production is killing off bacteria in the soil, which take methane out of the atmosphere.
In addition, while over-grazing causes soil degradation, which makes land unproductive, continuous crop production does so too and in fact of all farm crops only grass has the ability to take carbon out of the atmosphere and makes soils more resilient to climate change by increasing organic matter. All this shows there is no simple answer, but the detail in the various presentations below helps us begin the see a way forward to produce food more sustainably and more benignly in future.
Agricultural greenhouse gas emissions and sinks
Professor Pete Smith, University of Aberdeen – Reducing global meat consumption would improve the climate, food security and human health, so why is it not a no-brainer?
Dr Tom Misselbrook, Rothamsted Research – Ammonia and greenhouse gas emissions – who emits more?
Dr Ute Skiba, CEH Edinburgh – The role of nitrous oxide in the agricultural greenhouse gas budget, with focus on managed grasslands
Professor David Powlson, Rothamsted Research – Potential soil organic matter benefits from mixed farming: evidence from long-term experiments
Professor Richard Evershed, University of Bristol – The impact of agriculture on the soil methane sink
Richard Young – A Sustainable Food Trust perspective
Legumes, nitrogen and feed efficiency
Agri-environment schemes – are they fit for purpose? Rapporteur Dr Claire Horrocks
Carbon sequestration – can sequestration under grass be considered a valid offset for ruminant GHG emissions and could deep-rooting grasses, herbs and legumes sequester more? Rapporteur Ian Wilkinson
Mixed farming – would the reintroduction of mixed farming increase or lessen agriculture’s negative externalities? Rapporteurs – Professor Keith Golding and Robert Orr
Eat less meat – Which meats and why? Environment and human health. Rapporteur – Sue Dibb
Eat less meat – Which meats and why? Finite resources (including antibiotics) and human wellbeing. Rapporteurs – Richard Young and Amy Thomas
Meat and milk
Professor Ian Givens, University of Reading – Milk and dairy products: dietary partners for life?
Dr Michael Lee, University of Bristol and Rothamsted Research – Benefits of forage systems on product quality
Professor Kevin Shingfield, University of Aberystwyth – Benefits of forage systems on product quality: mechanisms and implications
Professor Mark Eisler, University of Bristol – Spilt milk worth crying over
Jerry Tallowin, Rothamsted Research – The biodiversity value of grassland – actual and potential
Dr Abi Burns, Royal Society for the Protection of Birds – Livestock: a perspective from RSPB
Dr Matt Reed, University of Gloucester – The silence of the barns: understanding the social and cultural importance of grazing animals to society
All of the presentations can be viewed through SlideShare.
Photograph: Steph French
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