Speaking at the First International Conference on Global Food Security held last month in the Netherlands, David Tilman, Regents Professor and McKnight Presidential Chair in Ecology at the University of Minnesota and professor at University of California, Santa Barbara‘s Bren School of Environmental Science & Management, presented his views on how we can achieve global food security and environmental sustainability.
Food insecurity and unsustainable use of the environment are two of the greatest challenges we as a society face. And they are linked: how we tackle one problem will affect the other. Prof. Tilman laid out the main barriers we face to achieving food security and environmental sustainability:
1) Increased demand driven by population and income growth
2) Dietary shifts and health including under and over nutrition
3) Environmental issues which include greenhouse gas emissions, nutrient pollution, ecosystem destruction and biodiversity loss.
Speaking to the second barrier in his list, Prof.Tilman explained that as income increases so does the demand for calories and animal protein. He pointed to the need for changes in dietary behaviour, without which it is unlikely we will address the world’s problems.
By 2050 global demand for crop protein will have increased by 110%, for crop calories by 100%. 30% of these increases will be a product of population growth, 70% from higher incomes, which are increasing most rapidly in poorer nations.
Changing our diets will not only address some of this growth in demand but it could also make us healthier. Recent evidence points to a 50 to 60% lower incidence of diabetes in lower meat diets. A pesco-vegetarian diet can add up to 10 years of life to a human adult, although there are multiple confounding factors that could bias this result. There is also a huge disparity in terms of access to meat, with half the global population having access to less animal protein than recommended under a low meat diet. So some people eat too much meat, some not enough.
Health benefits aside, a lower meat diet, for those with excessive meat consumption, also has environmental impacts in terms of agricultural production and how it expands. For example shifting towards greater production of fruits and vegetables, for which the whole world is underachieving in terms of eating the recommended amounts, less livestock and increased aquaculture.
Looking to the environmental sustainability challenge, Prof. Tilman explained that annual greenhouse gas emissions from fossil fuel combustion equate to almost 9 gigatonnes (Gt) of carbon equivalent, an amount that is hard to reduce given the world’s energy needs. If everybody drove a hybrid car, for example, this total amount would be reduced only by about one twentieth. At the moment it is hard to see how we will even reduce the rate at which emissions are growing each year. Greenhouse gas emissions from agriculture (not including fossil fuels which make up about 10% of agricultural emissions) are just under 4Gt of carbon equivalent per year, most of which comes from land clearing, livestock production and nitrogen fertilisation. If diets continue to change and yields continue on their past growth trajectories, by 2050 agricultural emissions will have increased by an additional 4Gt per year.
Looking at greenhouse gas emissions per kg of protein, we can see that outputs are far lower from plant sources as well as aquaculture and poultry than for such sources as beef, mutton, goat and trawling. Healthier diets could, therefore, reduce global agricultural emissions. Prof. Tilman explained that compared with an income-dependent diet, or business as usual, a low meat diet would result in no net increase in agricultural GHG emissions.
To date we have largely increased agricultural production through expanding agricultural lands and through greater fertilisation. Food production was doubled in the Green Revolution but use of nitrogen fertiliser increased by a factor of 7 and phosphorus fertiliser by a factor of 3. And these nutrients don’t always stay on the farm. They can leach into water supplies causing major health issues in the provisioning of clean water. One solution to the environmental impacts of fertiliser is precision agriculture, which involves:
1) The lowest effective N, P, pesticide and water uses at correct times; and
2) Use of crops that optimise nutrition per unit input and per hectare.
And there have been clear examples where reductions in inputs have been achieved largely through government regulation, such as the EU nitrate directive and the halting of fertiliser subsidies in Mexico. In some European countries and in Mexico, fertiliser use declined without a reduction in yield, sometimes maintaining the same yield growth trajectory.
Another aspect of environmental sustainability that needs to be addressed urgently is biodiversity loss. Biodiversity appears to be the single most important factor of sustaining ecosystem function. In the past 40 years we have cleared 600 million hectares of land for agriculture yet habitat loss is the biggest driver of biodiversity loss. If we continue on our current agricultural trajectory we will need to clear 800 million hectares of land or more by 2050. To put this in perspective, the US is about 900 million hectares in area. The majority of land clearing is expected to occur in the poorest countries where incomes and populations are growing and yet yields remain low. It is these same areas that hold the greatest potential to increase yields but their ability to do so is limited by a lack of capital, knowledge, inputs and infrastructure.
In a recent paper, Prof. Tilman and colleagues found that with moderate and efficient intensification in low yielding nations, only 150 million hectares would need to be cleared and agricultural emissions would reduce by some 2Gt carbon equivalent, mainly through land sparing.
There are many different trajectories to meet food demands but fewer trajectories which would leave the world with a sustainable and liveable environment. We need to use already cleared lands more efficiently and choose healthier and more environmentally friendly sources of protein. The current trajectories of food demand and agricultural production are a path to massive environmental damage, food inequity and less healthy diets. Strategic intensification of under-yielding cropland would provide more food in the nations where most malnourished people live and reduce greenhouse gas emissions and biodiversity loss.
Changing dietary behaviour would have massive beneficial impacts on health and the environment. But while we have the ability and technologies to intensify we do not yet understand how to change behaviour. Going vegetarian may not be for everyone, and it is not the only answer, but for most of us in the developed world, lowering our meat consumption seems to be a win-win.
Presentations from the First International Conference on Global Food Security are available here.
One Billion Hungry: Can We Feed the World? 
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