Simultaneous heatwaves in several breadbasket regions of the world could “fuel multiple harvest failures posing risks to global food security”, according to a study published in the journal “Nature Climate Change” on December 9th. The regions most affected by crop damages could be Western North America, Western Europe, Western Russia and Ukraine. For the study, an international team of scientists analysed large amounts of climate data covering the period 1979 to 2018. They focused on recurrent patterns in the jet stream, a fast-moving river of air that continuously circles the northern hemisphere from west to east. The wind system can develop large meanders, so-called Rossby waves. The researchers looked at two particular wave patterns which produce north-south wobbles in the jet stream: The wave-5 patterns tend to hover over central North America, eastern Europe and eastern Asia, whereas the wave-7 patterns affects mainly central/west North America, western Europe and western Asia. Both wave patterns have the same result: hot air swirls up from the south into the peaks, producing abnormal spikes in temperature that can last for weeks. This in turn reduces rainfall, dries up soils and vegetation, and kills crops in each region. As a consequence, food prices can soar, leading to social unrest, the authors warn.

“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 lead author Kai Kornhuber, a postdoctoral researcher at Columbia University’s Earth Institute. “During these events there actually is a global structure in the otherwise quite chaotic circulation,” said Kornhuber who is also a guest scientist at the Potsdam Institute for Climate Impact Research (PIK). “What makes this particularly relevant: the bell can ring in multiple regions at once,” he added. Those patterns can induce simultaneous heat extremes across several major breadbasket regions which account for up to a quarter of global food production. “Normally, low harvests in one region are expected to be balanced out by good harvests elsewhere,” said study co-author Dim Coumou from Vrije Universiteit Amsterdam and PIK. “These waves can cause reduced harvests in several important breadbaskets simultaneously, creating risks for global food production.”

The scientists showed that in years when amplified waves occurred during two or more summer weeks, crop production was affected negatively. The waves have hit in 1983, 2003, 2006, 2012 and 2018, when many temperature records fell across the United States, Canada, Scandinavia and Siberia. “During years in which two or more summer weeks featured the amplified wave pattern, cereal crop production was reduced by more than 10% in individual regions, and by 4% when averaged across all crop regions affected by the pattern,” said co-author Elisabeth Vogel from Melbourne University. Food-price spikes often followed. The authors warn that heat waves will almost certainly become worse in coming decades, as the world continues to warm. “We will see more and more heatwaves striking different areas at the same time, and they will become even more severe,” said Jonathan Donges, co-author from PIK. “This can impact food availability not only in the regions directly affected. Even remoter regions may see scarcities and price spikes as a result.” According to the authors, a thorough understanding of what drives jet stream behaviour in needed. This could help improve seasonal predictions of agricultural production at the global scale and contribute to better risk assessments of harvest failures across multiple breadbasket regions. (ab)