Is extreme heat changing where people live and work in the U.S.?

While the country is in the middle of yet another heat wave, “Marketplace Morning Report” is taking a closer look at how climate influences long-term patterns of where people live and work in the United States.

Among the mass migrations in U.S. history: after the Second World War, people left cold Snow Belt states in the Northeast and Midwest for the warmth of the southern half of the country. Americans are still moving south in large numbers, but new research documents some growing appreciation of colder parts of the country due to climate change.

Marketplace’s senior economics contributor Chris Farrell has been looking into this. He spoke with “Marketplace Morning Report” host David Brancaccio. The following is an edited transcript of their conversation.

David Brancaccio: All right, just remind us, 1950s and ’60s in particular — it was from the Snow Belt to the Sun Belt.

Chris Farrell: That’s right, there were a combination of factors. Millions of retirees, they were just fed up with the cold. They went for the warmth and recreational activities of the Sun Belt. Defense companies rose alongside military bases in the region. Established northern industries looking for cheap, nonunion labor shifted operations south. Agricultural businesses boomed, thanks to new farming techniques. So if you take a step back, David, newcomers were attracted by the region’s low cost of housing, the growth in job opportunities, low taxes and warm weather. And the widespread adoption of new technologies like air conditioning made the hot climate bearable.

Brancaccio: To be clear, people are still going to warmer places. But what is it that is making researchers wonder if that trend endures?

Farrell: Climate change. Global climate change. Think of the heat waves and heat domes that have driven temperatures to unsafe levels this summer in the Sun Belt. Americans are starting — and this is what two economists from the Federal Reserve Bank of San Francisco write — to “migrate away from areas increasingly exposed to extreme heat days toward historically colder areas, which are becoming more attractive as extreme cold days become increasingly rare.” And they reasonably speculate that climate change could even lead to a reverse mass migration pattern in coming decades.

Brancaccio: What are they using for data to get to that hypothesis?

Farrell: Their study, which to their knowledge is the first to document the shift in migration patterns, starts in 1951 but largely focuses on the period 1970 to 2020. And they match detailed county-level temperature data with county-level population and net migration data. Now, two definitions: “extreme heat” is defined as a day where the 24-hour average temperature is above 80 degrees. “Extreme cold” is when the average 24-hour temperature falls below 20 degrees or lower. Historically cold counties in the Snow Belt are becoming less cold over time, and hot Sun Belt counties are having more extreme heat episodes than before.

Brancaccio: So even with HVAC, and even if you don’t live anywhere near rising ocean levels, people are responding to climate change.

Farrell: That’s right. There was this really strong correlation between weather and internal migration in the U.S., but it’s weakened in recent decades. By the 2010 to 2020 period, the economists say there is little correlation between heat and migration. Maybe hot weather just isn’t as attractive these days to people living in cooler climates. And in some cases, we’ve even seen a reversal in the direction of migration. Hotter rural counties lost population over the last decade of data relative to colder rural counties. Also, hotter counties have recently witnessed declines among people with a four-year college degree.