The story of wheat as a cultivated crop is nearly as old as that of human civilisation itself. Few plants have played a bigger role in our history than the tall grass with its iconic amber kernels and wisps, which has fed cities, cultures and countries for some 10,000 years since it was first domesticated in the Middle East’s Fertile Crescent. Today, it has been bred, crossbred and modified thousands of times to fit any number of climates and locations worldwide.

It’s a hardy plant, capable of withstanding frost and other extreme temperatures. Partly because of that, wheat is now the most widely planted crop on the planet by land mass, with 217 million hectares (536 million acres) – an area the size of Greenland – devoted to growing it.

Milled, pounded, baked and boiled, wheat is a staple of cuisines across the world, from East Asia’s noodles and dumpling wraps to the iconic French baguette. The 1.2 billion metric tonnes of it that are grown every year now supply around a fifth of the total calories and protein consumed by human beings, in a global market that’s projected to be worth more than $200 billion by 2028.

Since the 1960s, the per-hectare yield of wheat has tripled — an incredible accomplishment, thanks in part to the development of more efficient and resilient strains of the plant, but also due to the heavy application of synthetic fertilizers in its cultivation. In the US, for example, 10% of all commercial fertilizer use goes to wheat; in China, a recent study showed that wheat had the highest fertiliser overuse rate of any cereal produced there.

But dumping all that synthetic fertiliser into the soil to make our pizza, pasta and udon noodles isn’t great news for the planet and wildlife. The two nutrients that give those fertilisers their growing power, nitrogen and phosphorous, have a nasty habit of leaking into the environment. In fact, most studies show that somewhere between 65% and 80% of the nitrogen in fertilisers either evaporates or washes into waterways after being applied to cropland.

That’s led to a massive, global ecological crisis directly tied to the way we produce food, including grains like wheat, as the amount of nutrients flowing around the planet’s biosphere has crossed a “planetary boundary” – a threshold that we need to stay behind in order to protect life as we know it.

Across the world, freshwater lakes, rivers and estuaries are experiencing toxic algae blooms, as the foul-smelling microorganisms feed on an all-you-can-eat buffet of nutrients lost to the environment from synthetic fertiliser, gunking up the water with green ooze and causing red tides. In coastal areas where rivers carry agricultural runoff into the ocean, these algae can use up all the oxygen and cause “dead zones” where no sea life can survive.

Wheat isn’t the only culprit in this problem. Corn and soybeans, often grown for animal feed, are a major cause of the Gulf of Mexico’s annual hypoxic dead zone, for example. But as the biggest occupier of agricultural land, wheat plays a big role.

Synthetic fertilisers are also a big contributor to the climate crisis. Most manufacturing methods require natural gas to be burned in order to produce them, and when they’re applied to fields they’re a major source of planet-heating emissions. Overall, 5% of total greenhouse gas emissions globally come from fertilisers, with one-third released during production and the rest through organic processes after they’re spread onto farmlands. As much as half of the carbon emissions produced by wheat come from this type of fertilizer evaporation.

In 2017, researchers set out to calculate the environmental cost of the average loaf of bread. They found that the biggest impact came from growing the wheat used to bake it, with around 40% of the damage they measured coming from the runoff of synthetic fertilisers into the environment.

Intensive wheat production also often involves heavy application of pesticides that can be harmful to biodiversity, killing insect populations that are necessary for healthy ecosystems elsewhere. Growing the amount of wheat that the world consumes takes a lot of water – in fact, it sucks up the second-highest quantity of any crop grown on Earth, after rice.

Compared to beef and other meat, though, wheat is a relatively minor contributor to climate change; in the US, it only accounts for about 1% of emissions. But climate change is almost certainly going to change what wheat production looks like worldwide in unpredictable ways. Surprisingly, some studies show that wheat yields could rise in some countries, as parts of the world become more temperate. But others show that it has a high vulnerability to extreme weather events like drought, which are set to become more common in the coming years.

That should raise alarm bells for some of the world’s major producer countries, including the US and India, both of which struggled with low-yield harvests in 2022 due to scorching heat and drought. Also, as production shifts toward higher and lower latitudes in a warming world, consumers in hotter, less wealthy countries could wind up in a tough spot, relying more on increasingly expensive imports as crops in their own countries fail.

To prepare for climate change, scientists are experimenting with the development of new, heat-resistant varieties. Many food systems experts are urging policymakers to move toward agricultural systems that approach fertiliser use differently. Studies have shown that planting nitrogen-fixing “cover crops” like legumes in rotation with wheat can reduce the need for fertilisers, for example, as could other farming practices associated with “circular” and “nature-inclusive” agriculture.

For more, here’s Mongabay’s look at the environmental impact of wheat for our “Consumed” series: