From 1914 – 1919, during which time World War I was being fought, an unusual weather pattern settled in over Northern Europe due to what’s called the North Atlantic Oscillation (NAO). This is a natural fluctuation that occurs in atmospheric pressure over the North Atlantic Ocean and has a strong effect on winter weather in Europe. It’s called an oscillation because changes in atmospheric pressure switch between a “positive” and “negative” mode in certain locations in the North Atlantic Ocean: it’s “positive” when there’s a strong subtropical high-pressure system over the Azores Islands and, over Iceland, there’s a strong low-pressure system; it’s “negative” when weaker high and low pressure systems are found over the same locations. During the World War I years, there was a lingering of the Icelandic low. Lows bring bad weather. It is well-documented that troops in the trenches during World War I suffered from abnormally cold, wet and muddy conditions, leading to hypothermia, pneumonia and other infections.
About a decade ago, up high in the Swiss Alps, scientists drilled an ice core, 73 meters long, that ending up spanning a more than 2000-year timeframe (this is found by counting layers and by looking for big identifiable “events” in the ice core, like a historic volcanic eruption, for which we know the date). Thus, clues in the ice – like ash deposits from volcanic eruptions, dust deposits from deserts, and constituents of sea salt from the ocean – can be used to infer past climate conditions. In this case, when the Icelandic low in the NAO dominates, winds come from the northwest, bringing more salty constituents to settle on snow/ice. When the Azores high dominates, winds come from the southeast, depositing dust from places like the Sahara Desert. In a nutshell, scientists working with this ice core found consistently high levels of sodium, chlorine and other constituents of sea salt during the war years – with peaks in the winters of 1915, 1916 and 1918 showing that, indeed, there was an extreme climate anomaly over Europe, where cold marine air from the North Atlantic settled in over the continent. It is thought that perhaps dust and chemicals produced by the war could have even impacted the weather patterns, prolonging them, as particulate matter obscured the sky and blocked the sun (leading to cold), while also acting as nuclei for clouds to seed upon and produce more rain.
The infamous Spanish Flu of 1918 killed tens of millions of people globally. While it did not come about due to the weather, weather may have played a role in turning it into a pandemic. How? The Spanish Flu first appeared in 1917 among American soldiers. It is widely thought that the flu originated as an avian flu – and it was found to particularly affect mallard ducks (with infection rates as high as 60%). Normally, European mallards migrate back and forth in northern Europe, passing through France and Germany in the process. Mallards are very sensitive to climate anomalies in their migration patterns, so it’s possible they didn’t follow their normal patterns, staying put in France and perhaps coming into close proximity with soldiers as they rotated in and out of the trenches, where the virus could have easily spread via polluted water. As the authors state in their paper, they’re “not saying that this was the cause of the pandemic but it certainly was an exacerbating factor” (Alexander More).
To get the full story on WWI, climate, disease and what lessons there are to be learned about the spread of disease, given what we’re dealing with currently with our own pandemic, COVID-19, check out this well-written article titled “Weather, Disease, and Lessons From Our Past”: https://www.tandfonline.com/…/10…/00431672.2021.1872986