July 7, 2012 — andyextance

If people like me in the developed world eat less steak, it could free up room for plants to reduce CO2 levels in the air driving climate change. That’s one forecast that has come from Tom Powell and Tim Lenton at the University of Exeter, who have studied how much space we’ll need for food in the future. “The impact on the environment of trying to produce the food demanded by the world’s population in the future could be disastrous, unless we make the production system much more efficient,” Tom told Simple Climate. “By far the easiest way to do this would be to cut meat eating, especially beef. Meat is likely to get more expensive as the resources needed to produce it become limited, and its environmental impact grows. Small changes to our diets and the ways we produce food have the potential to make what is currently a very environmentally damaging system a much more positive one.”

When we’re buying food, its climate impact may not be immediately obvious. But plants use the sun’s energy to take CO2 out of the atmosphere as they grow, storing that energy and CO2 in their bodies for a comparatively short time. “We can’t escape the links between our energy use, whether it’s for diet, industry or transport, and the carbon cycle,” Tom underlined. “Unfortunately, the carbon cycle also controls a sort of global thermostat, with the amount in the atmosphere as CO2 or methane influencing the climate.”

Tim and Tom noted that as the number of us on the planet grows, and we get wealthier, we are demanding more energy, both as food and fuel. “This is having damaging effects on ecosystems, and even on the world’s climate as the population grows toward 9.5 billion people all aspiring to a western lifestyle,” Tom underlined. As people get richer they also eat more meat – but meat production is hugely inefficient. Only about three or four parts in 100 of the feed energy livestock eat becomes food, with the rest lost as manure, heat, methane and slaughter by-products. Today, meat consumption provides one-sixth of the energy people across the world get from their food on average. However, people in rich countries eat much more meat, getting almost one third of their energy from it.

Plant power

Amid these worrying changes, the Exeter researchers wondered if there were ways that plants could be used for longer-term carbon storage, reducing the amount of CO2 in the atmosphere. “We wanted to see whether there was potential to reduce our destabilizing effect on the global carbon cycle through making some adjustments to the food and energy production systems we use at the moment,” Tom said.

One long-term storage method could be to decompose waste straw, manure and food wastes into charcoal at high temperatures without releasing CO2. This emerging process also produces some energy that could displace carbon emissions from generating electricity by burning fossil fuels. Such “biochar” can be mixed into farm soils to alter how acidic they are and how well they retain nutrients, while also storing carbon. Another longer-term storage option could be to burn biofuels made from plant or animal products and capture the CO2 they produce, though the technology to do this does not yet exist.

To consider these methods’ potential Tom and Tim looked at how the total mass of plants and animals both in farming and nature changes over time. They used UN Food and Agriculture Organization data for farming biomass, while for natural biomass they started from data on net primary productivity (NPP). This measures the amount of the sun’s energy fixed as carbon molecules by plants in a year using satellite pictures of plant growth and computer models.

These techniques show that human farming and forestry currently exploits about a quarter of this “plant power” available on land from about two-fifths of the surface. Using predictions of population growth and increasing wealth in developing countries, Tom forecasted food needs for 2050 and in turn how much NPP that would take, finding that a scaled-up version of today’s agricultural system would be a “catastrophe”. Almost three quarters of the Earth’s land surface had to be used as farmland, and the need to convert forests to extra farms would release large amounts of carbon into the atmosphere.

High steaks

In their paper, published in the journal Energy and Environmental Science last month, Tom and Tim therefore considered how food production and consumption could change. While they also looked at reducing and recycling more biomass waste, they found the amount of land needed to satisfy meat demand was most important. “As a result we slightly reduced the amount of meat in the average person’s diet or adjusted the types of meat people eat,” Tom explained. “A cow needs about 10 times as much food to produce the same amount of meat as a pig.”

These changes had a massive effect, meaning that after 2025 the amount of land needed to feed the world decreased. That freed up more land to produce more biochar, and is the only scenario where it makes sense to grow plants for biofuels. If that biofuel were used with carbon capture technology then that could reduce atmospheric CO2 levels, they predict. Currently, the atmospheric CO2 concentration is 396 parts of per million (ppm). The land use changes arising from continuing with our current ‘high-meat, low-efficiency’ approach could increase CO2 levels by 55 ppm, the Exeter researchers said. ‘Low-meat, high-efficiency’ agriculture could remove 25 ppm.

Tom added that we are already starting to eat more pork and chicken than beef. He also noted that achieving the “low-meat” scenario actually only needs us to get one part in 100 less energy from our food as meat on average. But keeping that average while the growing populations of developing countries eat more meat would require big changes for westerners. He also noted that while we might be eating less meat per person, this won’t necessarily be negative for livestock farmers. “There will always be a market for good quality grass fed meat,” Tom said. “Even in our scenarios where average meat consumption is reduced, the growing population still means that we need more animals overall. What we need to avoid are the large-scale factory farms that cause massive pollution, and the accompanying deforestation and environmental degradation to produce fodder for the animals they breed.”

Disclaimer: I’m friends with several people who work at the University of Exeter, though not the researchers in this study.