Back in 1374, Spain, Italy, and France were hit with famine due to the North Atlantic jet stream. The North Atlantic jet stream is a river of fast-moving air that flows from North America to Europe and during that time, it had moved north. The jet stream is what carries moisture-laden storm clouds and without them, southern Europe became dry, leaving crops to die. Hence, the famine.
Earlier this week, research was published in the Proceedings of the National Academy of Sciences restoring the history of the jet stream’s path in the North Atlantic from 700s AD to 2000. The conclusions suggest that high emissions could push Europe into a world similar to what happened in 1374 even if climate change has not changed the location of the crucial climate system yet.
Over the previous year, wiggles in the jet stream have been linked to extreme weather: from the floods in Europe that happened this spring to the heatwave that hit the Pacific Northwest. Amidst these extreme weather changes, the climate’s role in these movements is still undetermined.
“The jet stream is this wavy, buckling band of wind, but the mean position changes over longer time scales,” says the lead author of the study Matthew Osman and a climatologist at the University of Arizona.
The jet stream is in place held by polar air to the north and wind from the tropics to the south. It moves surface-level storms in its direction, or storm track, reforming rainfall all over huge regions.
“When the jet stream or storm track is situated further south, the already semi-arid regions of southern Europe receive a lot of moisture and mild temperatures,” says Osman. “But as the jet stream moves away towards the north, it takes away the storm track and precipitation and brings it to northern Europe.”
Osman also said that the move is not a huge deal when we think of it on daily or weekly periods but if we think about the forecasts of where deserts might be in the future, the moving moisture from dry regions to wet regions is a problem.
Getting sample cores from the Greenland ice sheet – which revealed records of rainfall and temperature dating back hundreds of years ago – researchers were able to reconstruct a record of the storm tracks all over the North Atlantic.
Researchers’ discovery found a remarkable amount of variability. “Observations have suggested that over the last few decades, the jet stream has started to migrate north,” said Osman. But the jet stream has moved north and south far and wide over the last 1,200 years that “it seems that the jet stream hasn’t emerged from what we might expect from natural variation alone.”
Even so, climate models imply that the jet stream will move northward and will move outside the historical zone by the year 2060 in the highest emissions circumstances, according to this research.
This only means that although we are now experiencing extraordinary smoke, rains, and fires during the summer, there are still many unknowns on the horizon that might come as more climatic systems push into unfamiliar territory.
The research did not indicate a similar historical context regarding the waviness of the stream which could potentially help solve the role of climate change in advancing extreme weather. Still, the research could determine a connection between some historical disasters and the jet stream.
“1728, 1740, these were years that winds blew at almost half their normal intensity…We know from historical documents that these were years that were really cold, where there was a really strong lack of precipitation.”
Back in 1740, the dreary weather caused a huge famine in Ireland which killed millions of people more than it killed during the Irish Potato Famine in the 1840s and 50s.
Jennifer Francis, acting deputy director at the Woodwell Climate Research Center, said it is a great test to find out if the models can realistically reproduce the conditions that we observe from the previous periods when it comes to human civilization.
“Anything that moves the jets closer to the pole is going to leave central Europe high and dry, which is going to favor drought conditions, and is associated with famines.”
Although not part of the study, she also gave two warnings. First is that according to her, climate models may be off in a few important ways that result in overestimating the tendency of the jet stream to move north. “There’s a lot of things to wonder about in terms of what the models project for the future latitude of the jet stream.”
Secondly, she said that the historical data ends in 2000 while the most visible effects of warming on the jet stream would have emerged within the last two decades.
“That would leave only a few years of, say, the Arctic starting to warm up, and that’s just not enough to see any impact on the jet stream.”
According to Osman, he believes that the climate has not yet reached the emergence of a new sort of climate regime and stresses that this means that humans can still head off movements to the jet stream since the system only evaded the historical norm in a high emissions situation. “That doesn’t have to be truth. It’s just a model.”