July 18, 2013 — andyextance

If the world’s poorer countries progress faster towards farming like richer ones the improved food availability could help fight climate change. That’s according to Austrian and Australian scientists who say that they have looked at climate change’s links to both animal and crop farming in the most depth yet.

Hugo Valin from the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria, and his colleagues studied cutting the gaps between farming output in rich and poor countries. They say halving this ‘yield gap’ for crops, and reducing it by a quarter for animals, could halve the increase in worldwide greenhouse gas emissions from farming between 2000 and 2050. But they have also found that improved farming methods could raise how much food people eat, meaning that emission reductions aren’t as much as they would be otherwise.

“The widespread idea is that intensifying crop farming is beneficial to the environment because it spares land,” Hugo told me. “We show that it is more complex than this. Intensification also stimulates consumption because it allows farmers to supply more food at affordable prices.”

Farming produces about a third of all ‘man-made’ greenhouse gas emissions, though a lot of them are actually from farm animals’ belches and farts and manure. The rest come from chemical reactions of fertiliser used on crops in soil, and also gases released from soil, plants and trees when forests are converted into farmland. Four-fifths of these emissions happen in developing countries. The world’s population is set to grow from around 7 billion people today to between 8.3 and 10.9 billion by 2050. We need more food for those extra people, which will add to the greenhouse gases farming puts into the air each year.

Growing yields

Thankfully, the amount of food farmers can get from a given area of land has been growing. Scientists have already shown that this has slowed the increase in greenhouse gas emissions from farming crops. That’s even after considering the emissions from making fertilisers and their later chemical breakdown. But no-one has looked at both crops and animals in this kind of research yet, or how improved farming’s effect on demand influences greenhouse gas release.

Therefore, Hugo’s team brought together their knowledge of crop and animal farming, and environmental economics to tackle these questions. To do that, they combined records of how farming has improved from 1970-2010 in the world’s different regions with moderate estimates of world population and economic growth. By putting this information into a computer model that brings together economics and plant growth across the world, they could project food supply and emissions in several different scenarios. Hugo stressed that this model, run by team member Petr Havlik, was critical to the team’s study. “This work has been possible only through the use of an integrated assessment tool that requires much effort in development and maintenance,” he said.

The scientists’ starting point assumed that farming will continue to improve as rapidly as it has in the past. Farmers would do this by using extra fertilisers, pesticides, irrigation, and machinery in crop farming, and better management of and greater investment in animal herds. They calculate that by 2050 meat production would still need to nearly double from 2000, and cereal farming increase by 72%, to supply enough food for the world. That would increase emissions from the equivalent of 3.5 billion tonnes of CO2 to 4.5 billion tonnes in this period, largely from changing forests into farmland.

What price more food?

In their study, which has just been published in Environmental Research Letters, Hugo’s team then added extra scenarios. In one, farming in developing countries and ‘economies in transition’ improved more slowly, half as quickly as they did in the past. In the other three farming in these countries improved faster. In one the crop farming yield gap fell by half. In another the animal farming yield gap fell by a quarter, and in the last one both these improvements happened together. They also looked at two other pathways to the final scenarios, one where crop farmers don’t use more fertiliser and one where technology saves farmers from any extra costs.

The slowest scenario added the equivalent of 0.34 billion tonnes of CO2 emissions, while improving both crop and animal farming cut 0.46 billion tonnes. The scientists found improving crop farming had a much greater impact on the food available than improving animal farming. However most emissions reductions came from animal farming, which cut 0.37 billion tonnes, while improved crop yields alone cut the equivalent of just 0.07 billion tonnes of CO2 emissions.

The small impact of crop improvements comes partly because they require more fertiliser, which adds extra emissions. However, half as much extra emissions again comes because more abundant feed makes meat cheaper, meaning that it’s eaten and farmed more widely. But halving the crop yield gap without using fertilisers would see the CO2 emission cuts increase to the equivalent of 0.24 billion tonnes. Meanwhile, the pathway that reduced farmer costs raises food output but limits climate benefits.

Hugo’s team now wants to go on and model the impact of other demands on farming, such as for crops as energy sources. He also wants to figure out the economic and physical reasons why yield gaps exist at all. But he’s already confident that at least some of these gaps can be narrowed. “There is evidence that agricultural practices can be much improved in many developing countries,” he said. “The question is how to unlock these improvements. Regions such as Asia or Latin America have had some success. This implies removing many economic constraints. Farmers need access to credit to invest in capital and technology and to markets to obtain inputs and sell products. And the countries need to develop the capacity to resist extreme events, as well as improving health, education, and their institutions.”

Journal reference:

H Valin, P Havlík, A Mosnier, M Herrero, E Schmid and M Obersteiner (2013). Agricultural productivity and greenhouse gas emissions: trade-offs or synergies between mitigation and food security? Environmental Research Letters DOI: 10.1088/1748-9326/8/3/035019