According to research led by climate scientist and historian Alexander More from Harvard University and published in the journal GeoHealth, unusual bad weather occurring from 1914 to 1919 worsened the effects of World War I, lasting from July 1914 until November 1918, and the 1918-19 pandemic.
During World War I along the Western Front in Europe, stretching from the English Channel to the Alps, soldiers struggled not only against each other, but also through the torrential rains and unusually cold weather. The shell holes and the trenches were filled with cold, stagnant water, resulting in the feared trench foot, a medical condition caused by prolonged exposure of the feet to damp, unsanitary, and cold conditions. The incessant rain mixed with soil and debris formed a sticky mud on the battlefield, reducing the mobility of soldiers and horses and making it near impossible to move heavy equipment like artillery. In the mountains, the cold weather claimed more lives than the actual combat operations. Alone in the winter of 1916 more than 10,000 soldiers died in the Alps crushed to death by avalanches.
In late spring 1918, a deadly virus appeared without warning, claiming victims among the combatants as civilians. At first, few deaths were reported. Victims recovered after a few days. When the disease surfaced again that fall, it was far more severe. Some victims died within hours of their first symptoms. Others succumbed after a few days; their lungs filled with fluid and they suffocated to death. Within months, the 1918 flu pandemic had killed an estimated 50 million people – more people than any other illness in recorded history.
Studying an ice core from the European Alps, the research reconstructed the climate conditions from 1914 to 1919 over Central Europe. Unusually strong influxes of cold marine air from the North Atlantic, primarily between 1915 and 1919, resulted in unusually strong precipitation events, forming a recognizable peak of chloride- and sodium-rich dust in some layers of the studied ice core. The occurrence of the layers was then compared to mortality rates experienced in Europe during the same time period, as well as historical weather records from the front. The researchers found correlations between peak periods of mortality and periods of cold temperatures and heavy precipitations in the Alps and along the front lines, especially during the winters of 1915, 1916, and 1918.
The authors of the study also cautionarily consider that the bad weather helped to spread the virus responsible for the 1918 flu pandemic.
The bad weather over central Europe didn’t affect not only humans, but also animals. Especially migratory birds were forced to alter the migratory patterns. Instead of migrating to Asia or Africa at the end of summer, many species remained in Europe and near the cities during the wet and cold autumns. It is possible that some migratory bird species, like mallard ducks, known to be carriers of the avian influenza virus, helped to spread the flu. Through their fecal droppings, these birds could have contaminated bodies of water sourced by humans and other animals.