Global warming already causing crop losses of over $20 billion a year

Heatwaves and drought, driven by global warming, are already reducing maize, wheat, and soybean yields by $20 billion annually, according to a study. If emissions are not reduced, this loss could multiply eightfold to exceed $160 billion by 2100.

Major producers like the US will bear the largest financial losses, but the greatest impact will be on the poorest countries where most people work in agriculture, explains Yi Ling Hwong from the International Institute for Applied Systems Analysis (IIASA) in Austria. In Africa’s least-developed nations, the consequences will be more severe, potentially leading to social unrest and increased migration, she warns.

There is significant uncertainty surrounding these predictions due to the variable nature of farmers’ responses and adaptations to climate change, such as switching crops or implementing irrigation where feasible. The study aims to raise awareness and encourage adaptation to make these projections overestimates, says Kai Kornhuber, also from IIASA. “The mission of climate scientists is to present scenarios for people to react, ensuring our projections are proven wrong.”

The research team collected data on maize, wheat, and soybean yields per country from the UN Food and Agriculture Organization (FAO). They then analyzed historical climate data to assess drought levels using a standard method that calculates soil moisture from rainfall and evaporation.

By comparing past heat extremes and drought levels with yields from 1974 to 2004, the team estimated the impact of these factors on crop yields. They used these correlations to assess crop losses from 2007 to 2019, finding that increased heat and drought have led to a 3.5% reduction in yields compared to the 1974-2004 baseline. “While 3% may not seem significant, it can have a major impact on the global food market, potentially triggering a severe crisis in some regions,” says Kornhuber.

The study also calculated economic losses based on FAO data, which reflect what farmers could have earned for their produce at the time. The researchers then projected future losses under various emissions scenarios, assuming some adaptation occurs.

In a high-emissions scenario, referred to as SSP3-7.0, global yields could decline by around 35% by 2100, with annual losses exceeding $161 billion. “Production losses from heat and drought amount to about 855 million tonnes a year,” says Hwong, who presented these findings at a European Geosciences Union meeting in Vienna. “This is roughly equivalent to what 2 billion people consume annually.”

This analysis might underestimate the full impact of climate change, as it considers only three crops and excludes flood, storm, or rain damage, as well as potential price hikes for other crops like coffee and cacao.

Jonas Jägermeyr from Columbia University in New York cautions that relying on statistical relationships between yield losses and extreme heat and drought could exaggerate the impacts by 2100. “Statistical yield models are useful for understanding current and recent trends, but they are unreliable when extended to drastically different environmental conditions, such as high-emission scenarios at the century’s end.” He suggests computer models that simulate plant responses to rising CO2 and temperatures are more reliable for long-term projections.

Karine Chenu from the University of Queensland, Australia, agrees, stating that models are better suited for such extrapolations. Her team recently published a study, not yet peer-reviewed, indicating that two common wheat models make large errors and perform poorly in predicting the combined effects of extreme heat and drought.

However, Kornhuber defends the use of statistical methods, stating, “Models are powerful tools, but some validation studies suggest they may not respond well to extremes. Our project focused on extremes, so we chose to establish these relationships through statistics.”