Fossil fuels help us grow food. That’s good for food production but bad for the planet.

You probably know that if you want to help cut greenhouse gas emissions, you shouldn’t eat meat or other animal products – at least not every day. Now, researchers have come up with some numbers that may help stiffen your resolve to change your diet.

Animal husbandry is hugely inefficient. We first produce edible products and then we feed these edible products to animals to get a much smaller fraction of the calories back.

In a new article, researchers from Norway, Austria and Switzerland have calculated just how much energy it takes to put livestock products and other foods on our tables.

It turns out that animal-based products were responsible for almost 60 per cent of the energy footprint of agriculture worldwide in the period from 2015-2019.

That energy is predominately from fossil fuels, said Edgar Hertwich, a professor at NTNU’s Industrial Ecology Programme and senior author of the new paper.As societies are working to moving towards renewable energy, they are often choosing electricity as a green alternative, Hertwich said.

“But what's the solution for agriculture?” he said. “Animal husbandry is hugely inefficient. We first produce edible products and then we feed these edible products to animals to get a much smaller fraction of the calories back.”

As a result, livestock, with their giant energy footprint, provided just 18 per cent of the calories consumed worldwide in 2015-2019, the latest period for which the researchers had data.

Calculated energy return on investment

The researchers, led by Kajwan Rasul, a researcher at NTNU’s Industrial Ecology Programme, calculated how much energy it takes to produce the food the world eats.

And, how much energy – in the form of edible food, measured in calories – does the world get from this investment?

Rasul and his colleagues calculated an “energy return on energy investment” to assess how efficient – or not –  the world’s food system actually is.

In this case, if the energy return on the energy invested is a number less than 1, it takes more energy to grow the food than that food provides in the form of calories.

Rasul used two models for his work. One is called EXIOBASE, which they used to estimate the energy use of different sectors of the economy. The second model, called FABIO, contains information about the production, trade and consumption of food.

“Coupling these two models using novel techniques made it possible to analyse the energy use in the food system in much more detail than previously possible,” Rasul said.

The researchers used 10 food product groups (aggregated from 123 different commodities) and divided the world into 20 regions. They looked at two 5-year periods, 1995-1999 and 2015-2019, to be able to identify trends.

Some trends are positive

Rasul found that the energy efficiency of global food systems overall improved from 1995 to 2019, with the energy return on energy investment shifting from 0.68 in 1995 to 0.91 in 2019.

Although that’s a clear improvement, it still meant that in 2019, “for every human-edible calorie provided to society, 10 per cent more energy was needed to produce it,” Rasul and his colleagues wrote.

Countries with less industrialized food systems, such as East and West Africa and South and Southeast Asia, consistently had energy returns on investments that were higher than one.That’s good because these regions are home to 68 per cent of the world’s population. The top performer, West Africa, had an energy return on energy investment of 2.70.

This improvement was also noticeable for four of the world’s five high-income regions, but Rasul isn’t sure that this trend is truly due to efficiency improvements.

“That the energy efficiency of the food systems that high-income regions rely on has increased in the last couple of decades was a positive surprise,” he said. “However, that could be due to a shift to a more calorie-intense diet or an increased reliance on imports from regions that have better conditions to produce food in a more energy-efficient way.”

Confirming this idea will require additional research, Rasul said.

Food security and energy security

If energy for food production was limitless and without an environmental impact, we wouldn’t necessarily care about inefficiencies in agriculture, Rasul and his colleagues wrote.

In addition to the climate aspects of inefficient food production, however, there’s another aspect the researchers have highlighted: food security. If we depend on fossil fuels to endlessly support our agriculture, we could be in for a big shock.

This is not just theoretical: During the energy crisis of the 1970s, Arab oil exporters imposed an embargo on exports to the United States, with ripple effects in the Western world, causing both food and energy prices to skyrocket.  More recently, the war in Ukraine has had the same result.

Agricultural systems that rely on fossil fuels “turn the question of food security into a question of energy security,” Rasul and his co-authors wrote.

The articlehas been published in PNAS Nexus, a publication of the National Academy of Sciences of the United States.