Ukraine brings in the harvest, now at risk from the jet stream. Image: By Voice of America (public domain), via Wikimedia Commons

Food shortages and civil disturbances may result from changes in the jet stream winds which circle the Earth, scientists say.

LONDON, 10 December, 2019 − Patterns in the winds of the jet stream that circles the Earth can bring simultaneous heatwaves to breadbasket regions which provide up to a quarter of global crops, scientists have found.

Extreme weather on this scale can significantly harm food production, making prices soar and fuelling social unrest. Western North America, western Europe, western Russia, Ukraine and the Caspian Sea region are especially susceptible.

In a study published in the journal Nature Climate Change the researchers, from Germany, Australia and the US, explain how specific wave patterns in the jet stream strongly increase the chance of heatwaves occurring at the same time in different parts of the globe.

The jet stream is a fast-moving river of air that continuously circles the northern hemisphere from west to east. It generally confines itself to a relatively narrow band, but can meander north or south, due to a feature scientists call Rossby waves.

Among other effects, these atmospheric wobbles may pull frigid air masses from the polar regions, or hot ones from the subtropics, into the populous mid-latitudes.

“We will see more and more heatwaves striking different areas at the same time, and they will become even more severe”

The wobbles strongly influence daily weather. When they grow particularly large they can bring prolonged heatwaves, droughts or floods in summer, or in colder seasons abnormal cold spells.

The waves have hit in 1983, 2003, 2006, 2012 and 2018, when many temperature records fell across the US, Canada, Scandinavia and Siberia. As well as killing crops, the waves have killed thousands of people, especially in Europe and Russia, where air conditioning is far less common than in North America.

The research shows that there has been a significant increase in the probability of multiple global breadbasket failures, particularly for wheat, maize, and soybeans. For soybeans the implications of crop failure in all major breadbaskets associated with climate risk would be at least 12.55 million tons of crop losses, far more than the 7.2 million tons lost in 1988–1989, one of the largest soybean production shocks.

Kai Kornhuber, a doctoral candidate from the Potsdam Institute for Climate Impact Research (PIK) in Germany and the Lamont-Doherty Earth Institute, US, and colleagues found that it is these simultaneous heatwaves that can significantly reduce crop production and create the risk of multiple harvest failures and other far-reaching consequences.

Twentyfold increase

“We found an under-explored 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 Kornhuber. “During these events there actually is a global structure in the otherwise quite chaotic circulation.”

The atmospheric patterns the team researched mean that heat and drought become locked into one place simultaneously, where they then affect crops’ production yields.

“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.

“Normally low harvests in one region are expected to be balanced out by good harvests elsewhere. But these waves can cause reduced harvests in several important breadbaskets simultaneously, creating risks for global food production”, said co-author Dr Dim Coumou from the Institute for Environmental Studies at VU Amsterdam and PIK.

Remote effects

“We will see more and more heatwaves striking different areas at the same time, and they will become even more severe”, added Dr Jonathan Donges, another co-author at 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.”

“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 Elisabeth Vogel, from Melbourne University.

Ted Shepherd, professor of climate science at the University of Reading, UK, who was not involved in the study, said: “We have strong observational evidence of this wave pattern. What is open for discussion is how it might respond to climate change.”

Professor Shepherd said many consensus scientific statements, including those from the Intergovernmental Panel on Climate Change, had proved to be under-estimates of how fast and far the effects of global warming might move. − Climate News Network