What impact does wheat have on the climate and environment?
The emissions caused by growing wheat differ from country to country and are heavily influenced by growing environments and inputs used. For example, in the US, one study estimated that each kilo of wheat grown in the US in 2010 caused 1.1kg of CO2e emissions. For China, this was estimated at 0.75kg of CO2e per kilo in 2013.
The use of fertilisers, pesticides, diesel-fed heavy machinery and subsidised electricity from fossil fuels for irrigation all play a part in wheat’s environmental footprint. Then, there are emissions from direct and indirect land-use change from growing wheat for food or biofuels, which are not always easy to estimate.
Most significant among these is wheat’s reliance on nitrogen (N) fertilisers, produced by the highly energy-intensive Haber–Bosch process that depends on fossil fuels, as does its transport from production centres.
Nearly a fifth of the world’s nitrogen-based fertiliser is deployed to grow wheat. However, wheat is the least efficient major crop for nitrogen use, taking up less than half of the nitrogen applied. The rest finds its way into ecosystems and the atmosphere via a “nitrogen cascade”, harming the biosphere, soil fertility, water systems and contributing to climate change.
Nitrogen can leach as nitrate into water sources, resulting in algal blooms and aquatic “dead zones”. A notable example is the New Jersey-sized dead zone in the Gulf of Mexico, downstream from the grain fields of the US midwest. Microbes in the soil also convert nitrogen to nitrous oxide, a greenhouse gas with 300 times the heat-trapping capacity of CO2.
Compared to other commodities, such as soy, coffee, beef and corn, wheat has smaller deforestation and biodiversity impacts, but they vary from country to country. However, large-scale wheat production does have significant land-use impacts, depleting soil carbon while also contributing to the reduction in native crop and diet diversity.
For example, in the US, 53m acres of the Great Plains grasslands were converted to cropland every year between 2009 and 2015. Ploughing of this land resulted in CO2 emissions equivalent to 670m extra cars on the road, according to a report produced by WWF, along with reductions in biodiversity and soil fertility. Wheat accounted for 21% of new land conversion in the northern Great Plains, said a 2021 report.
Pesticides used on wheat crops around the world also have myriad impacts on society. On the one hand, farmers need to manage pests to avoid substantial yield and economic losses, especially in food-insecure wheat-growing countries, but also in countries where new farmland is not available.
On the other hand, their prolonged use has long-term impacts on human health, climate, biodiversity and ecosystem services. Overreliance has other consequences: Australia’s wheat farmers have been facing their worst weed crises ever, stemming in part from herbicide use. In Punjab’s wheat belt, hundreds board a Cancer Train every day to seek treatment in the neighbouring state of Rajasthan, their illness widely blamed on pesticide use and pollution.
Wheat can also contribute to water stress. It takes an average of 1,500 litres of water to produce one kilogram of grain. Wheat production can, therefore, be a major competing demand for water.
For example, 47% of the “groundwater footprint” of global wheat production lies in the Indus and Ganga river basins which are densely-populated regions. Punjab’s groundwater resources board estimates that the water table up to 300 metres could be “completely exhausted” within 20 years.
For countries that typically import wheat, this impact is outsourced. For example, Italy consumes twice the global average of wheat per person. But close to half its total wheat water footprint lies abroad, especially in the US and France, which are both experiencing droughts that are harming wheat harvests.
