It is convenient to blame agriculture for emissions that occur when land is converted for agriculture. Over the 12,000 years since we figured out how to rear livestock and grow crops, agricultural practices produced around a third of cumulative emissions from human activity. Most of this is from land clearing.
Emissions from land clearing happen because land without native trees, shrubs, grasses and herbs supports less biomass with a more rapid turnover of the biomass it does have compared to natural vegetation. Greenhouse gases are also released from soil when exposed to the elements as rates of soil organic matter (SOM) decomposition tend to increase without the protection of vegetation cover.
Agricultural practices themselves are also emission sources.
Fossil fuels drive tractors and a dizzying array of farm machinery.
Industrial processes use energy and fossil fuel as raw materials to make inorganic fertilisers.
Crop residue burning also releases carbon. For example, about 2 million farmers in northwest India burn an estimated 23 million tons of rice residues annually. In the cities of northwest India, particulate air pollution can exceed the safe daily threshold limit by more than five times, demonstrating in real time that this is an emission problem.
Then there is methane, a greenhouse gas with a GWP (global warming potential) 27 times greater than CO2, that is emitted from flooded soils under rice cultivation, enteric fermentation in the digestive systems of livestock, and the decomposition of manure and crop residues under wet conditions.
Nitrous oxide (GWP 23 times that of CO2) is released from soils fertilised with nitrogen, manure, and compost that release inorganic nitrogen into the soil.
According to the FAO, the league table for the most significant emissions from agricultural practices is
- enteric fermentation (40%),
- manure left on pasture (16%),
- synthetic fertilizer (16%),
- paddy rice (10%),
- manure management (7%)
- burning of savannahs (5%)
Here is a summary of the volume of these emissions relative to the total in 2014 from a recent global research review using IPCC data.
Source: Jat, M. L., Chakraborty, D., Ladha, J. K., Parihar, C. M., Datta, A., Mandal, B., … & Gerard, B. (2022). Carbon Sequestration Potential, Challenges, and Strategies towards Climate Action in Smallholder Agricultural Systems of South Asia. Crop and Environment.
Even without the fossil fuel burning that powers the farm machinery, the land clearing, and the industries that produce the inputs, agriculture accounts for over 20% of global emissions from human activities thanks to methane and nitrous oxide, upwards of 10 Gt CO2e per year.
South Asia is home to just shy of 2 billion people, one-quarter of all the people on the planet. Population growth and climate effects are expected to increase food demand in the region by 40% by 2050.
There are two massive challenges to meeting this demand.
First, 94% of the land suitable for farming is already under production. This means there is very little scope for agricultural expansion by area.
The second challenge is that 58% of agricultural areas are already under stress from water shortage, extreme heat stress, and poor soil health. The production area is not in great shape. Conventional cultivation practices with exhaustive tillage and removal of crop residues by burning or for other uses result in nutrient and C losses and the air pollution problem.
The imperative to grow enough food that requires net production to increase at over 1% per annum for the next 30 years forces inputs. Such a system must rely on fossil fuel inputs to keep up with demand.
Only this cannot happen, either. Cost of inputs, availability and the emission consequences of inputs in production systems that produce methane and nitrous oxide will combine to make industrial production challenging. Farmers will be under immense pressure to make ends meet.
Perhaps only small-scale production that use the soil’s natural capacity to renew and circulate nutrients on the farm will be viable.
Why are agricultural emissions about ecology?
Emissions of greenhouse gases from fossil fuels are a human construct. We found the fuel and burnt it in our machines. And we use those machines in agriculture and the industrial processes that generate agricultural inputs.
Then we use energy to transport, store, process, retail and cook food. The food supply chain is a massive energy sink.
And we could stop there.
Many industrial countries did just that and kept agriculture from any emissions targets they set to combat climate change.
Greenhouse gas emissions are a consequence of agricultural practices and the food system that comes after the food is grown. And those practices that produce crops and livestock products are about changing the way ecology works. Agriculture alters nature to channel as much biomass production from the land as possible into the parts of plants and animals that humans like to eat.
Modern agriculture is subsidiesed by external energy sources to augment production, to make the ecology faster and more efficient for the products we desire, but it doesn’t have to be.
There is enough capacity and capability in nature to produce enough food without the inputs but not without huge changes to consumer expectations, consumption, behaviours and to farming practices.
What sustainably fed suggests
Agriculture is responsible for a third of historic and ongoing greenhouse gas emissions. We could lay blame or ignore this truth when attempting to set emissions reduction targets, as many countries have done.
But as we always say, the 22 trillion calories a day challenge to feed people has to be met somehow or risk the ugly consequences of failure.
We suggest a reset.
Let’s look again at agriculture as an ecological process and retrofit or replace the current food production systems with ones closer to nature.
This will mean many people will eat less and differently. It will mean more farmers and much shorter supply chains. It will mean farms that recycle nutrients and do more with fewer inputs.
And it will be a wild ride.
Jat, M. L., Chakraborty, D., Ladha, J. K., Parihar, C. M., Datta, A., Mandal, B., … & Gerard, B. (2022). Carbon Sequestration Potential, Challenges, and Strategies towards Climate Action in Smallholder Agricultural Systems of South Asia. Crop and Environment.
Hero image from photo by José Guimarães on Unsplash