Well-documented torrential rains and unusually cold temperatures affected the outcomes of many major battles during World War I from 1914 to 1918. Poet Mary Borden described the cold, muddy landscape of the Western Front as “the liquid grave of our armies” in her poem “The Song of the Mud” about 1916’s Battle of the Somme, during which more than one million soldiers were killed or wounded.

The bad weather also affected migratory patterns of mallard ducks, the main animal host for the H1N1 influenza virus strain responsible for the “Spanish Flu” pandemic that claimed more than 50 million lives from 1917 to 1919.

Scientists recently discovered a once-in-a-century climate anomaly brought the incessant rain and cold to Europe during the war years, increasing mortality during the war and during the flu pandemic in the years that followed.

The findings show how changes in Earth’s climate can exacerbate human conflicts and pandemics. But other research shows the reverse effect: how human pandemics can alter the environment.

A 2017 study found levels of lead pollution in the atmosphere dropped to basically zero during the infamous Black Death pandemic of 1349 to 1353. The findings showed human activity has polluted European air almost uninterruptedly for the last 2,000 years and only a devastating collapse in population and the economy reduced atmospheric pollution to natural levels.

In this episode, climate scientist and historian Alexander More describes the relationship between climate and pandemics in the context of these two seemingly unconnected pieces of research and discusses what humans can learn from pandemics of the past.

This episode was produced by and mixed by Lauren Lipuma.