Extreme weather patterns associated with heat waves and droughts are raising the risks of simultaneous harvest failures of vital crops worldwide, such as wheat, maize, and soybeans, two studies found. This is pushing the world closer to the edge of potential food price spikes, associated social unrest, and food shortages.

The studies, published in the journal Nature Climate Change, found that in an increasingly interconnected world, there’s a greater chance that extreme weather events can have ripple effects in more than one region at once.

In particular, when the jet stream — the high altitude air current that steers storms and separates air masses, takes on more undulating and persistent wavy shapes, extreme heat events become more common in particular parts of the world. These locations include the breadbasket region of western North America as well as western Europe, western Russia, and west Asia, depending on the jet stream pattern that develops and locks into place.

A key conclusion of the study is that simultaneous heat extremes, and resulting decreases in food production, are possible in locations separated by thousands of miles. When particular weather patterns, known as “wave number 5” and “wave number 7” for the number of jet stream peaks, or ridges, as well as dips, or troughs, are present, the probability of simultaneous heat extremes in these regions increases by a factor of up to 20 for the most severe heat events, the study found. This is the case when either of these two extreme weather patterns dominate the atmosphere.

According to the study, if two or more weeks of a summer are spent locked into one of these weather patterns, then regional crop production could see decreases of up to 11%, or 4% when averaged across all of the affected areas.

“We found an underexplored vulnerability in the food system: when these global scale wind patterns are in place, we see a twenty-fold increase in the risk of simultaneous heatwaves in major crop producing regions,” said Kai Kornhuber, an atmospheric scientist at Columbia University and at the Potsdam Institute for Climate Impact Research. “What makes this particularly relevant: the bell can ring in multiple regions at once and the impacts of those specific interconnections were not quantified previously.”

Low harvests in one location tend to be balanced out through trade by plentiful harvests elsewhere, but the new studies show that there’s a real possibility that extreme weather patterns can cut the productivity of several of the world’s so-called “breadbasket” regions simultaneously.

Kornhuber said it’s well-known that heat waves will become more intense, and therefore more damaging, if emissions of planet-warming greenhouse gases are not reduced regardless of any changes in these jet stream patterns. “In general, extremes will become stronger and the likelihood that extremes will occur simultaneously will also increase,” Kornhuber said.

In addition, some studies have shown that global warming may be making the jet stream wavier, and more likely to get locked into persistent patterns.

“Global warming can also affect the circulation and potentially make these wave patterns more persistent or provide favorably conditions for those patterns to recur,” Kornhuber said.

He said the study’s results enable researchers to use climate models that would analyze the risks of multiple harvest failures in different warming scenarios.

Michael Mann, a climate scientist at Penn State, said the study is interesting but limited in scope. “It’s an interesting article and the science looks solid to me,” he said. He noted, though, that the data used in the study are highly variable, or “noisy,” which makes the identification of clear trends more difficult.

The jet stream study could suggest a way forward for early warning systems to highlight the potential for food supply disruptions before they occur.

A second study examined how temperature and precipitation extremes have been changing from a spatial perspective, and compared that to the location of global food producing regions. Researchers found that the risk of simultaneous breadbasket failures have increased.

The study showed that the likelihood of multiple breadbasket failures increased substantially for all crops (wheat, maize, and soybean) examined except rice between 1967-1990 and 1991-2012.

The study notes that food price spikes in recent years have led to social unrest, including the pronounced spike during 2007-2008, which preceded the Arab Spring. Studies have also tied climate extremes in Syria as one of the contributors to civil unrest and forced migration.