Climate change is making rollercoaster harvests the new normal

(Press-News.org) From corn chips to tofu, climate change is messing with the menu.

A new global study led by the University of British Columbia shows that hotter and drier conditions are making food production more volatile, with crop yields swinging more sharply from year to year. For some, it may mean pricier burgers; for others, it can bring financial strain and hunger.

Published today in Science Advances, the study is the first to show at a global scale how climate change is affecting yield swings of three of the world’s most important food crops: corn, soybean and sorghum. For every degree of warming, year-to-year variability in yields rises by seven per cent for corn, 19 per cent for soybeans and 10 per cent for sorghum.

While previous research has focused on climate-driven declines in average yields, this study highlights a compounding danger: instability.

For many farmers, those swings aren’t abstract. They’re the difference between getting by and going under.

“Farmers and the societies they feed don’t live off of averages—they generally live off of what they harvest each year,” said Dr. Jonathan Proctor, an assistant professor at UBC’s faculty of land and food systems and the study’s lead author. “A big shock in one bad year can mean real hardship, especially in places without sufficient access to crop insurance or food storage.”

Boom, bust, repeat

While average yields may not plummet overnight, as year-to-year swings grow, so does the chance of “once-in-a-century” crop failures, or very poor harvests.

At just two degrees of warming above the present climate, crop disasters could become more frequent. Soybean crop failures that once struck once every 100 years would happen every 25 years. Corn failures would go from once a century to every 49 years, and sorghum failures to every 54 years.

If emissions continue to grow , soybean failures could hit as often as every eight years by 2100.

Some of the regions most at risk are also the least equipped to cope, including parts of Sub-Saharan Africa, Central America and South Asia, where many farms rely heavily on rainfall and have limited financial safety nets.

The consequences won’t be limited to lower-income regions. In 2012, for example, a drought and heatwave in the U.S. Midwest caused corn and soybean yields to drop by a fifth, costing the U.S. billions and sparking concern in markets around the world. Within months, global food prices jumped nearly 10 per cent.

Double trouble

To understand how these overlapping stresses affect crops at a global scale, the researchers combined global harvest records with high-resolution measures of temperature and soil moisture from stations, satellites and climate models.

“A key driver of these wild swings? A double whammy of heat and dryness, increasingly arriving together,” said Dr. Proctor. 

Hot weather dries out the soil. Dry soil, in turn, makes heatwaves worse by allowing temperatures to rise more quickly. And climate change intensifies these processes.

“If you’re hydrated and go for a run your body will sweat to cool down, but if you’re dehydrated you can get heatstroke,” said Dr. Proctor. “The same processes make dry farms hotter than wet ones.” 

Even brief spells can slash yields in these conditions—disrupting pollination, shortening growing seasons and stressing plants beyond recovery.

For soybeans and sorghum in particular, the growing overlap between heat and moisture explains a large portion of the increase in volatility.

Irrigation can help—if water is available

Irrigation can effectively reduce yield instability, the study shows, where irrigation water is available. Many of the most at-risk regions, however, already face water shortages or lack irrigation infrastructure.

To build resilience, the authors call for urgent investment in heat- and drought-resistant crop varieties, improved weather forecasting, better soil management and stronger safety nets, including crop insurance. But the most reliable solution is to cut emissions driving global warming.

“Not everyone grows food, but everyone needs to eat,” said Dr. Proctor. “When harvests become more unstable, everyone will feel it.”

The study, “Climate change increases the interannual variance of summer crop yields globally through changes in temperature and water supply,” was co-authored with Lucas Vargas Zeppetello (University of California, Berkeley), Duo Chan (University of Southampton), and Peter Huybers (Harvard University).

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