Since Russia’s full-scale invasion of Ukraine on 24 February 2022, the world’s food systems have been shaken in ways few could have predicted. As two of the largest exporters of staple grains, Russia and Ukraine together once supplied nearly one‐third of global wheat and almost one‐fifth of maize to the world market.

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When conflict disrupted these flows, grain prices surged, leaving food‐importing countries scrambling for supplies. At the same time, higher prices encouraged farmers in other regions to convert forests, grasslands, and wetlands into new cropland—releasing large amounts of carbon dioxide into the atmosphere and undermining global climate‐change goals.

Background and Study Design

Before diving into the results, it helps to understand why Russia and Ukraine matter so much to global food security, and how the researchers structured their analysis. First, Russia and Ukraine are powerhouse grain exporters. In 2021, Ukraine alone accounted for about 12 percent of global wheat exports and 15 percent of sunflower-oil shipments, while Russia added another 19 percent of world wheat exports and 14 percent of maize.

Consequently, any major interruption in their exports sends prices soaring on international markets. Low-income, food-importing countries are particularly vulnerable, since they spend a larger share of their national budgets on food.

Second, higher grain prices do not only affect consumers. They also send signals to producers worldwide, who respond by planting more. In many cases, farmers expand into natural ecosystems—whether converted pasture, grassland, peatland, or forest—because they can charge higher prices for their crops.

Such land-use change releases carbon stored in soils and vegetation, adding to global greenhouse-gas emissions and working at cross-purposes with climate-change mitigation efforts.

To capture these complex dynamics, the study coupled a well‐known global agricultural partial-equilibrium trade model with a carbon-accounting framework that estimates emissions from land conversion.

The trade model projects how farmers adjust planting decisions over one full growing cycle (roughly one year) in response to price changes, while the carbon model applies average emissions factors—measured in tonnes of CO₂ per hectare—to quantify greenhouse gases released when new cropland replaces natural land.

Importantly, the analysis focuses on responses in every country except Russia and Ukraine, since reliable production data for those two nations are scarce amid war. The researchers considered a baseline scenario of normal trade patterns and four disruption scenarios, each reflecting different degrees and types of export bans or production cuts.

Commodity Price Changes

One of the clearest and most immediate effects of disrupted grain flows is on international commodity prices. When Ukraine’s exports drop to zero for one year, the model forecasts that global wheat prices climb by about 3.6 percent and maize by 3.9 percent relative to the baseline. These are sizeable jumps that strain food budgets, especially in countries that rely heavily on imports for their staple grains.

Moreover, when the study adds a 50 percent cut in Russian grain exports on top of Ukraine’s ban, wheat prices surge by 7.2 percent and maize by 4.6 percent. This larger spike in wheat reflects Russia’s especially heavy role as a wheat supplier. At the same time, prices for other crops vary: for example, sunflower-oil prices leap by over 60 percent when exports from both countries are restricted, because Ukraine dominates that market.

However, cutting biofuel mandates in the European Union and the United States by half offers a partial respite for some crops. Since maize is a key input for U.S. ethanol and rapeseed for EU biodiesel, reducing biofuel demand eases pressure on those markets.

In fact, under that scenario, global maize prices fall by 0.8 percent and rapeseed prices drop by 5.4 percent compared to the baseline. Yet wheat prices remain elevated—about 3.5 percent above baseline—because ethanol policy changes do not address the shortage of wheat that would have come from Ukraine.

Finally, the model examines a scenario in which Ukrainian production itself falls by half, for instance due to damaged infrastructure, but without a formal export ban. In that case, wheat prices rise by a more moderate 2.9 percent and maize by 2.8 percent. This scenario underscores how much greater the market disruption is when exports are entirely halted rather than merely constrained by lower production.

Production and Trade Responses

Higher prices naturally prompt farmers and traders worldwide to adjust their behaviors. When Ukrainian exports vanish, key wheat producers outside Russia and Ukraine ramp up output substantially. For instance,

India increases its wheat exports by over 70 percent,
the European Union by around 36 percent,
and the United States by roughly 24 percent.

Argentina, Australia, and Canada also boost shipments, though to a lesser degree. Correspondingly, for maize, Brazil and the United States raise exports by about 14 percent and 16 percent, respectively.

That said, when biofuel mandates are slashed, U.S. maize exports rise less than under export-ban scenarios, and Brazil’s maize shipments actually dip slightly. Essentially, freeing up corn from ethanol shifts production incentives regionally, demonstrating that policy levers can influence how and where farmers respond to price signals.

Cropland Expansion

Crucially, production increases outside Russia and Ukraine require more land. In the scenario with only a Ukrainian export ban, other countries convert roughly 11.1 million hectares of natural land into cropland—an area about the size of Cuba. When both Russia and Ukraine face export cuts, total cropland conversion swells to about 18.2 million hectares.

Conversely, halving EU and U.S. biofuels limits land expansion to around 6.6 million hectares, since farmers lose some incentive to grow maize and rapeseed for fuel. Under the scenario of a 50 percent production drop in Ukraine (but no export ban), cropland elsewhere rises by approximately 8.3 million hectares, striking a middle ground.

Carbon-Emissions from Land Conversion

Turning biodiverse ecosystems into farmland releases enormous quantities of stored carbon. By applying standard emissions factors to newly converted cropland, the study estimates that a Ukrainian export ban alone generates about 1,011.2 million tonnes of CO₂ equivalent (MtCO₂e) from land-use change—more than the annual emissions of many industrialized countries. When Russian exports also fall, land-use emissions exceed that figure, though the precise number is not detailed in the paper.

In contrast, cutting biofuel mandates in the EU and U.S. cuts land-use emissions roughly in half, to about 527.2 MtCO₂e, because the demand shock for maize and rapeseed is smaller. To put these numbers in perspective, reducing biofuels by 30 percent in the United States and the EU can lower land-use emissions by 188.8 to 468.1 MtCO₂e—depending on the carbon-stock assumptions.

In other words, the agricultural shifts induced by the Russia–Ukraine conflict rival or even exceed the climate impact of significant biofuel policy changes. Such findings highlight the stark trade-off: while expanding cropland helps fill supply gaps and stabilizes prices to some extent, it locks in substantial carbon emissions that counteract efforts to mitigate climate change.

Food Security Implications

Higher grain prices have direct human consequences, particularly in low-income, food-importing countries where households spend a large share of their income on staples. Even modest price increases translate into meaningful drops in caloric intake.

According to the model’s results, per-capita consumption changes across cereals range from a decline of 1.2 percent to a slight increase of 0.1 percent when only Ukraine’s exports are halted. When both Russia and Ukraine curtail exports, consumption falls by up to 2.0 percent in some regions, though a few areas see marginal gains if they benefit from reconfigured trade flows.

Reducing biofuel use mitigates some of these declines—limiting consumption drops to about 1.0 percent at most—since more maize becomes available for food rather than fuel. Finally, a production cut in Ukraine of 50 percent yields consumption changes within roughly 0.8 percent of baseline.

Yet even these seemingly small percentage declines can aggravate undernourishment among already vulnerable populations. After all, a 1–2 percent drop in daily calories can push millions more into food insecurity. Moreover, unequal price increases mean that poorer households—who have less room in their budgets—bear the brunt of the shock.

Consequently, governments and international agencies must recognize that commodity-price stabilization alone does not ensure food security. Unless measures are taken to protect the most vulnerable—through targeted subsidies, cash transfers, or direct food aid—the human toll could be severe.

Policy Recommendations

Given the intertwined challenges of food security and climate change, the study suggests a suite of complementary policy actions.

First, temporarily reducing biofuel mandates in the United States and the European Union can free up significant quantities of grains for food and feed markets, dampening price spikes for maize and rapeseed. However, biofuel cuts alone cannot fully compensate for wheat lost from Ukraine, so they must be part of a broader strategy rather than a standalone fix.

Second, keeping trade channels open is vital. Even if Ukrainian ports face security risks, every shipment that can safely depart reduces global shortages. Likewise, avoiding export bans from Russia—or lifting them if they are already in place—allows surplus grain to flow where it is needed most, helping contain price increases and reducing the need for environmentally damaging land expansion elsewhere.

Third, providing targeted food assistance to low-income, import-dependent countries can protect vulnerable households from acute price shocks. Mechanisms such as vouchers, subsidies, and in-kind aid—coordinated through international bodies like the World Food Programme—can help ensure that higher world prices do not translate into hunger on the ground.

Fourth, investing in sustainable intensification offers a longer-term solution. By improving crop varieties, adopting precision-farming techniques, and optimizing fertilizer use, farmers can raise yields on existing farmland, reducing the incentive to clear new land for cultivation. International cooperation to share best practices and technologies can accelerate these yield gains in developing countries.

Fifth, diversifying supply sources and building strategic reserves can enhance resilience. Countries that rely heavily on a single exporter or a handful of crops should explore alternative suppliers and maintain buffer stocks to cushion against future disruptions—whether caused by conflict, climate extremes, or other shocks.

Finally, strengthening agricultural infrastructure and market access in low-income regions can reduce post-harvest losses and lower transaction costs, helping more of the harvested crop reach markets and consumers. Improved storage facilities, better roads, and efficient port operations can all play roles in stabilizing local food systems.

Conclusion

The war in Ukraine has underscored how intertwined global food security and climate objectives have become. Disruptions to Russian and Ukrainian grain exports sent shockwaves through agricultural markets, driving up prices, reducing food consumption among the world’s poorest, and spurring cropland expansion that released over one billion tonnes of CO₂ equivalent in the most severe scenario.

While other producers can partially fill the void—especially when policy tools like biofuel-mandate adjustments are deployed—the environmental cost is steep. Consequently, policymakers face a complex balancing act: they must secure affordable food supplies for vulnerable populations today without sacrificing the planet’s capacity to mitigate climate change tomorrow. A coordinated, multi-pronged approach is essential.

Power Terms

Global agricultural trade model: A global agricultural trade model is a computer-based tool that simulates how countries buy and sell farm products like grains, oilseeds, and livestock feed. It uses data on production, consumption, prices, and trade costs to predict how markets adjust when conditions change—for example, when a major exporter stops selling wheat. This model is important because it helps policymakers and analysts foresee shortages, price spikes, or surpluses before they happen. In practice, analysts input a shock—such as an export ban—and observe the model’s output on production changes, price shifts, and trade flows. For instance, if maize exports from Ukraine drop to zero, the model might show how much extra maize Brazil would need to export to fill the gap.

Carbon-accounting framework: A carbon-accounting framework is a systematic method for measuring greenhouse-gas emissions, especially carbon dioxide released by human activities. It assigns “emissions factors” (for example, tonnes of CO₂ per hectare of forest cleared) and multiplies them by the area or activity level to estimate total emissions. This framework is vital for understanding the climate impact of land-use changes—such as converting grassland to cropland—and for tracking progress toward emissions targets. A simple formula is:

For example, if a region converts 1 million hectares of peatland (with an emission factor of 100 tCO₂e/ha), the resulting emissions would be 100 million tonnes of CO₂ equivalent.

Partial-equilibrium model: A partial-equilibrium model focuses on a single sector—like agriculture—ignoring interactions with other parts of the economy. By contrast, a general-equilibrium model covers all sectors simultaneously. The partial-equilibrium approach is useful because it requires fewer data and less computation, yet still captures key supply-and-demand dynamics within farming, trade, and food markets. For example, when global wheat prices rise, a partial-equilibrium model shows how wheat planting areas expand and how wheat exports shift among major producers, without modeling unrelated sectors such as manufacturing or services.

Land-use change: Land-use change refers to the conversion of natural landscapes—forests, grasslands, wetlands—into agricultural or urban areas. This process is significant because it often releases large amounts of carbon stored in plant biomass and soils, making it a major contributor to climate change. Moreover, land-use change can reduce biodiversity, affect water cycles, and lead to soil erosion. An example is clearing the Amazon rainforest to plant soybeans: while this expansion boosts soybean supply and may lower prices, it emits carbon and destroys wildlife habitat.

Biofuel mandate: A biofuel mandate is a government rule requiring that a certain percentage of vehicle fuel come from biological sources, such as ethanol made from corn or biodiesel made from rapeseed. Mandates aim to reduce reliance on fossil fuels, support farm incomes, and cut carbon emissions. However, they can also divert crops from food and feed markets, raising prices for consumers. For instance, a 10 percent ethanol mandate means that 10 percent of all gasoline sold must be blended with ethanol. Reducing such mandates can free up crops for food use, easing supply pressures during a grain shortage.

Export ban: An export ban is a government policy that prohibits the shipment of certain goods—such as wheat or maize—outside the country. Nations sometimes impose bans to keep domestic prices low or to ensure local food security during times of scarcity. While effective in stabilizing internal markets, export bans can exacerbate global shortages and drive up international prices. For example, if Country A bans wheat exports, importing nations must turn to other suppliers, often at higher cost, which can trigger worldwide price spikes.

Baseline scenario: A baseline scenario represents “normal” or expected market conditions without any shocks or policy changes. It serves as the reference point against which all disruption scenarios—such as export bans or production cuts—are compared. By maintaining constant production, consumption, and trade flows, the baseline helps analysts isolate the effects of specific events. For instance, in the study, the baseline assumes no changes in Russian or Ukrainian exports; all percentage price changes in other scenarios are measured relative to that baseline.

Production cut: A production cut is a reduction in the volume of goods a country or region produces. In agriculture, a production cut might occur because of severe weather, infrastructure damage, or pest outbreaks. A 50 percent production cut in Ukraine, for example, means farmers harvest only half the usual amount of wheat and maize. This cut can push up global prices, even if exports are not officially banned, because the overall supply available to world markets shrinks.

Price signal: A price signal is information conveyed by market prices that tells producers and consumers how to adjust behavior. When prices rise, farmers receive a positive signal to plant more, while consumers may buy less or switch to substitutes. Conversely, falling prices discourage production and encourage consumption. Price signals thus coordinate market responses without direct government intervention. For example, a 7 percent jump in wheat prices signals farmers worldwide that growing wheat has become more profitable, prompting them to expand acreage.

Cropland expansion: Cropland expansion is the process of increasing farmland area by converting other land types into agricultural use. It is driven by the need to produce more crops when prices rise or demand grows. Although it helps meet short-term food needs, cropland expansion often leads to habitat loss, reduced biodiversity, and carbon emissions. The study estimates that, under certain conflict-driven export cuts, global cropland could expand by up to 18 million hectares—roughly the size of Syria.

Greenhouse-gas emissions: Greenhouse-gas (GHG) emissions are gases—such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O)—that trap heat in the Earth’s atmosphere, leading to global warming. In agriculture, GHG emissions arise from land-use change, fertilizer use, livestock digestion, and machinery fuel. Measuring and reducing these emissions is critical for climate-change mitigation. The study quantifies land-use-change emissions in CO₂ equivalent, highlighting how agricultural shifts contribute substantially to global GHG totals.

CO₂ equivalent (CO₂e): CO₂ equivalent is a standard unit for measuring the combined impact of different greenhouse gases based on their global-warming potential (GWP). It expresses the warming effect of a gas—like methane or nitrous oxide—as if it were an equivalent amount of CO₂. The formula is:

For example, methane has a GWP of about 28 over 100 years, so 1 tonne of CH₄ equals 28 tonnes CO₂e. Using CO₂e allows policymakers to compare and add emissions across gases.

Per-capita consumption: Per-capita consumption measures the average amount of a good—such as calories or kilograms of grain—consumed per person within a population. It’s calculated by dividing total consumption by population size. Per-capita metrics help track nutritional intake and food security. For instance, if a country consumes 10 million tonnes of maize and has 20 million people, per-capita maize consumption is 0.5 tonnes per person.

Import-dependent country: An import-dependent country is one that relies on foreign suppliers for a significant share of its food or other essential goods. Such reliance makes these nations vulnerable to external shocks—like export bans or transport disruptions. For example, a small island state importing 80 percent of its wheat faces high risk if major exporters halt shipments; its food security depends on diversified supply chains or strategic reserves.

Food security: Food security exists when all people have physical, social, and economic access to sufficient, safe, and nutritious food that meets their dietary needs. It encompasses availability (enough food), access (affordable and reachable), utilization (nutritious and safe), and stability (consistent supply over time). Conflict-driven price spikes and export cuts threaten food security by reducing availability and affordability, especially for poor households.

Sustainable intensification: Sustainable intensification means producing more food from existing farmland while minimizing environmental impact. It involves practices such as precision agriculture, improved seed varieties, efficient irrigation, and integrated pest management. By boosting yields without expanding land area, sustainable intensification helps achieve food security and climate goals together. For example, drip irrigation can increase crop output by delivering water directly to roots, reducing water usage and runoff.

Crop diversification: Crop diversification is the strategy of growing a variety of crops rather than relying on a single staple. This practice spreads risk—pests, diseases, and market fluctuations affecting one crop are less likely to ruin an entire harvest. Diversification can also improve soil health and nutrition security. For instance, rotating maize with legumes like beans can naturally replenish soil nitrogen, reducing fertilizer needs and enhancing yield stability.

Strategic grain reserves: Strategic grain reserves are stocks of key cereals—such as wheat, rice, or maize—held by governments or international organizations to cushion against supply shocks and stabilize prices. Reserves can be released to domestic markets or exported to alleviate global shortages. The management formula often balances storage costs against the insurance value:

Well-managed reserves can prevent hunger during conflicts, natural disasters, or price spikes.

Yield gap: The yield gap is the difference between actual crop yields achieved by farmers and the maximum potential yields under optimal conditions. Closing this gap through better seeds, fertilizers, and farming methods can boost food production without expanding farmland. For example, if maize yields average 5 tonnes per hectare but could reach 10 tonnes under best practices, the yield gap is 5 tonnes per hectare.

Price elasticity of demand: Price elasticity of demand quantifies how much the quantity demanded of a good changes in response to a price change. It is calculated as:

A value greater than 1 indicates high sensitivity (elastic demand), while less than 1 means low sensitivity (inelastic). In the context of staple grains, demand is often inelastic—people need basic calories—so even large price hikes cause only small reductions in consumption, increasing the risk of hardship for poor households.

Trade resilience: Trade resilience refers to the ability of global and regional markets to absorb shocks—such as export bans, conflicts, or natural disasters—without severe disruptions to supply and prices. Building trade resilience involves diversifying import sources, maintaining transparent trade policies, and investing in logistics infrastructure. For example, when one exporter falters, resilient systems quickly shift to alternative suppliers, minimizing price spikes and shortages.

Land-conversion emissions factor: The land-conversion emissions factor is a value that estimates how much CO₂ (or CO₂e) is released when a specific land type—like forest, grassland, or peatland—is converted to cropland. It is expressed in tonnes of CO₂e per hectare. For instance, a tropical peatland converted to agriculture might emit 100–200 tCO₂e/ha, whereas a temperate grassland might release 30 tCO₂e/ha. These factors are crucial inputs for carbon-accounting frameworks.

Ethanol: Ethanol is an alcohol-based biofuel typically made by fermenting sugars from crops like corn, sugarcane, or wheat. It’s blended with gasoline—often at 10–15 percent—to reduce fossil-fuel use and greenhouse-gas emissions. Ethanol’s importance lies in its renewable nature, yet it competes with food markets; diverting corn to ethanol can tighten supplies and raise food prices. A common blend in the United States is E10, containing 10 percent ethanol and 90 percent gasoline.

Biodiesel: Biodiesel is a renewable fuel produced by chemically reacting vegetable oils or animal fats with an alcohol (usually methanol) to create fatty acid methyl esters. It can be used in diesel engines with little or no modification. Biodiesel reduces certain emissions but, like ethanol, competes with food crops—such as rapeseed or soybean oil—potentially affecting food-oil prices. Common blends include B5 (5 percent biodiesel) and B20 (20 percent).

Agricultural intensification: Agricultural intensification means increasing the output of food per unit of land, labor, or inputs. It can involve higher fertilizer use, more irrigation, mechanization, or adopting high-yield crop varieties. While intensification raises productivity and can spare land from conversion, it also carries risks—such as nutrient runoff, water depletion, and increased greenhouse-gas emissions if not managed sustainably. For example, precision fertilizer application can achieve intensification while limiting environmental harm.

Reference:

Carriquiry, M., Dumortier, J. & Elobeid, A. Trade scenarios compensating for halted wheat and maize exports from Russia and Ukraine increase carbon emissions without easing food insecurity. Nat Food 3, 847–850 (2022). https://doi.org/10.1038/s43016-022-00600-0

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