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 published Monday 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 (technically known as “Rossby waves,” after the scientist Carl-Gustaf Rossby), extreme heat events become more common in particular parts of the world. These locations include the breadbasket regions of western North America, Western Europe, western Russia, and western Asia, depending on the exact jet stream pattern that develops and locks into place.

A key conclusion of one of the studies 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, regional crop production could see decreases of up to 11 percent or 4 percent 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,” Kai Kornhuber, an atmospheric scientist at Columbia University and at the Potsdam Institute for Climate Impact Research, said in a news release. “During these events there actually is a global structure in the otherwise quite chaotic circulation.”

“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,” Kornhuber said.

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

In an interview, 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 favorable conditions for those patterns to recur,” Kornhuber said.

Kornhuber 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 who has studied climate-change-related shifts in Rossby wave patterns, said the new study is interesting but limited in scope. “It’s an interesting article and the science looks solid to me,” Mann said via email. “It is a useful exercise in understanding the circumstances under which one observes simultaneous extreme weather events and the role of amplified Rossby waves with those extremes.” He noted, though, that the data used in the study are highly variable or “noisy,” which makes the identification of clear trends more difficult.

Mann was not involved in the new research.

The jet stream study could suggest a way forward for early-warning systems to highlight the potential for food supply disruptions before they occur, rather than well after they’ve developed, though much more work would need to be done to get to that point.

Multiple ‘breadbaskets’ could fail at the same time

A second study took a different, more Earthbound route to researching food production failures. By examining how temperature and precipitation extremes have been changing over time from a spatial perspective and comparing that to the location of global food-producing regions, the researchers found that the risks of simultaneous breadbasket failures have already increased.

The study showed that the likelihood of multiple breadbasket failures increased substantially for all crops (wheat, maize and soybean) examined, except rice, between the periods of 1967 to 1990 and 1991 to 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 called climate extremes in Syria one of the contributors to civil unrest and forced migration.

“If there is a crop failure in one single major crop producing region (breadbasket), they can be leveled out by surpluses in other breadbasket regions through trade. However, this is not possible anymore when multiple breadbasket failures happen in the same year, which then poses a real threat to global food security,” said study lead author Franziska Gaupp, a researcher at the International Institute for Applied Systems Analysis in Austria.

“Generally speaking, an important impact of multiple breadbasket failures are price spikes which hit poorer countries (where people spend a higher share of their income on food) the hardest,” Gaupp said.

The study did not investigate how climate change may be altering the characteristics or likelihood of the jet stream patterns, nor did it show how climate change is altering heat waves. However, other studies have addressed these issues. For example, one study published in Science Advances in 2018 projected there may be a nearly 50 percent increase in the incidence of stalled weather patterns that lead to extreme events in a warmer climate.

Another study, published in 2017, found global warming has increased the severity and probability of the hottest month and hottest day for more than 80 percent of the globe that has adequate instrument weather records.

In a major report released in August, the U.N. Intergovernmental Panel on Climate Change also raised alarms about the increasing possibility of food crises developing on multiple continents at once because of climate change, land degradation, desertification and other threats.