German immigration to the United States in the 19th century was partly due to climate

In 1874, Germans immigrated to the United States on the Hamburg ship. (?Everett Historical/Shutterstock) “KDSP” Today, Germany is the top immigration destination after the United States. But in the 19th century, Germans fled their homeland in large numbers in search of better overseas prospects.

In that era, more than 5 million Germans immigrated to North America, including Donald Trump and the Heinz family ancestors. And now, new research suggests climate is a major factor in this migration pattern.

"To this day, the migration from Europe to North America is the largest migration in history," said Rüdiger Glaser, professor of geography at the University of Freiburg in Germany. Glaser said most literature on immigration in Germany usually blames the phenomenon on political and social issues. [Refugee Crisis: Why there is no science for resettlement]

The 19th century was indeed a period of major political and social upheaval in Germany, from the wars of the Napoleonic era, to the bourgeois revolution of 1848, to the industrial revolution , and then to the establishment of the German Empire in 1871. But Glaser and his colleagues wanted to test the hypothesis that climate may be an important factor in causing such large-scale migration movements, using statistical modeling to focus their study on areas around their university. The region, now the state of Baden-Württemberg in southwestern Germany, has detailed records of immigration, population, weather, harvests and grain prices in the 19th century. (This region was not the Germany we know today; in 1815, the beginning of the study time frame, it was cobbled together from the Grand Duchy of Baden, the Kingdom of Württemberg, and the Kingdom of Prussia.)

They used a complex statistical model to try to quantify the impact of climate on migration. Overall, Glaser said, about 30 percent of the immigrants who moved from that corner of Germany between 1815 and 1886 can be explained by a series of events that started with climate: harsh climatic conditions led to low crop yields, This causes grain prices to rise, which causes people to want to pick up and leave in search of better opportunities. "10 surprising ways weather has changed history," Glaser said. "It's clear." The knock-on effects are compelling.

"This is not surprising when you consider that the majority of the population in southern Germany at the time was rural and household livelihoods and incomes were closely tied to agricultural productivity," Wilfrid Laurier University said Associate Professor Robert McLeman of Canada, who was not involved in the study.

McLeman said people tend to associate environmental migration with environmental refugees, or the sudden displacement of large numbers of people from their homes by storms, floods and single major events. "While events like this do occur periodically, we often overlook the longer-term, more subtle effects of climate and environment on migration patterns," McLeman told Live Science. He added that the report shows "how climate affects migration indirectly, by affecting market prices for commodities and damaging household livelihoods."

Glaser and his colleagues found that some surges in migration were associated with particularly severe climate related to the incident. For example, the massive eruption of Mount Tambora in Indonesia in 1815 sent enough ash into the atmosphere to cause global chaos. 1816 is known as "The Year Without a Summer" because farmers in the Northern Hemisphere experienced poor harvests due to rising grain prices.

Other migration flows have more obvious geopolitical implications. The researchers found that the surge in immigration between 1850 and 1855 occurred during the Crimean War, when France banned food exports, squeezing Germany's grain market.

The Baden authorities tried to get rid of the poor during this time by subsidizing their immigration (partly in the hope of preventing riots)