Climate Anomaly Affected Mortality in WWI and the Spanish Flu Pandemic

EMBARGO DATE: Thursday, September 24th, 2020, 9AM EST
Media contact: Dr. Alexander More,
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New interdisciplinary research shows that a once-in-a-century climate anomaly that brought torrential rain and cold air over Europe for six years also affected the casualties of World War I battles and the Spanish Flu Pandemic, the largest such pandemic in modern times, and the most widespread even in comparison to COVID-19. The new data addresses why the Spanish Flu killed people in the months it did, in a lethal second wave during a wet autumn.

The findings have been published today in a new article in the journal GeoHealth with the American Geophysical Union. The study is based on evidence from this period that combines for the first time epidemiological, historical, and new climate records from an ice core in the European Alps.

figure 4 modified from More et al 2020

The ice-core data was produced by using next-generation laser technology available only at the Climate Change Institute at the University of Maine, where climate scientists analyzed one of the most detailed climate records in existence. Historians and public health experts at the Initiative for the Science of the Human Past at Harvard and at the University of Nottingham collected and analyzed the mortality and other records detailing the impact of the climate anomaly.

The Spanish Flu Pandemic caused an estimated 50 million casualties and infected 500 million people, one third of the world’s population a century ago. It emerged at the end of World War I, in the spring of 1918. In the fall of 1918, a very severe second wave of the pandemic caused millions of deaths worldwide.

The new evidence shows that extremely high precipitation in the fall of 1918 matched the pattern of the pandemic’s mortality. The increased precipitation was part of a longer, six-year climate anomaly that brought rain and cold air from the North Atlantic over Europe, in a sustained Icelandic low pressure system. The cold, rainy conditions affected several infamous battles of World War I, including the Somme and Ypres III-Passchendaele, where torrential rain caused trenches to flood and turned battlefields into lakes of mud, as recorded by eyewitnesses. Famines and the disruption of migratory patterns of wildlife—particularly the mallard duck, one of the main reservoirs and vectors of the H1N1 influenza—also likely contributed to weakening the population and increasing mortality.

“It’s interesting to think that very heavy rainfall may have accelerated the spread of the virus,” said Philip Landrigan to AGU. Dr. Landrigan is director of the Global Public Health Program at Boston College and was not connected to the new study. “One of the things we’ve learned in the COVID pandemic is that viruses seem to stay viable for longer in humid air than in dry air. So it makes sense that if the air in Europe was full of humidity during those years of World War I, that the transmission of the virus might have been accelerated.”

Figure 3
Figure 3, from the new article, showing a double peak in precipitation and mortality of the
Spanish Flu pandemic, and a similar pattern during WWI battles.

The research is the result of a collaboration of the Initiative for the Science of the Human Past at Harvard and the Climate Change Institute at the University of Maine, with ongoing contributions from researchers at from the University of Nottingham, in the U.K. The Historical Ice Core Project is funded by Arcadia, a charitable fund of Lisbet Rausing and Peter Baldwin.

Arcadia fund logo