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Flee the melt. Following the Last Glacial Maximum, species seemed to die off en masse in regions experiencing rapid shifts in temperatures (shown in yellow and red), but they held on in many hilly regions like the Andes (inset).

Brody Sandel (map); Dennis Pedersen (photo)

Glacial Melting Put Animals on the Run

Cool-weather animals, put on your running shoes. A new study of historic climate patterns suggests that, as our current world warms, slower-moving critters may go extinct in far greater numbers than their speedier counterparts. The findings highlight the importance of giving animals enough room to move freely in the face of future climate change, researchers say.

Nearly 21,000 years ago, during what scientists call the Last Glacial Maximum, thick ice tracts swaddled much of North America and Europe. Then, over thousands of years, those glaciers began to melt and dribble away. Ancient creatures across the globe from bats to frogs faced a difficult decision: adapt to the hotter conditions or move, usually north or up mountains, to chase the receding cooler breezes.

In a 2009 paper published in Nature, researchers coined the term "climate velocity" to describe the pace of such mass migrations. They weren't just interested in the past—they were concerned about the future. As the world warms, many species will once again be forced to flee, says Scott Loarie, a biogeographer at the Carnegie Institution for Science at Stanford University in Palo Alto, California, who coauthored the 2009 study.

To get an idea of how such a mass migration may decide the fate of the world's diverse fauna, researchers turned the clock back to the Last Glacial Maximum. They drew on estimates of how fast temperatures changed in the thousands of years following that maximum, indentifying regions of rapid climate shifts. In parts of modern-day Canada or Northern Europe—"high velocity" regions—animals likely had to migrate close to 100 meters per year to keep within their ideal environments. These relatively speedy shifts may have driven local animals to extinction, says Brody Sandel, who studies ecoinformatics at Aarhus University in Denmark. Those same areas today host very few endemic mammals, birds, or amphibians—species that stick to one spot and one spot only, he and colleagues report online today in Science.

Scientists had long suspected that some local animals might not be able to outrun climate change, but researchers haven't yet been able to prove the hypothesis, says Loarie, who was not involved in this study: "It's just wonderful to see empirical evidence that backs this up."

The animals' fates may have come down to speed, Sandel adds. For instance, amphibians, the "tortoises" in this tortoise-and-a-hare race against climate change, seemed to die off much more than fast-moving animals, the hares, such as many birds. Flying mammals also survived more on average: "If we split mammals into bats and nonflying mammals, bats behave kind of like the birds."

How fast species need to move may depend on how hilly their homes are, Sandel suggests. He points to Denmark as an example: This uniformly flat region doesn't host a single endemic mammal, bird, or amphibian. That's because temperatures tend to be uniform across uniform landscapes, he says, meaning that animals will have to migrate long distances to reach cooler locales, putting locals at greater risks of extinction during times of change.

The opposite is true for mountainous regions. Take the American pika, which lives along mountains in the western United States: To get to cooler weather, all these squeaky critters need to do is climb a few hundred meters uphill.

Long migrations could have big consequences for conservation in the face of future climate change, Sandel says. If animals can't move freely from one habitat to the next, then rare species could become stuck in sweltering conditions.

But scientists should use caution when applying the fates of animals during the Ice Age to the modern era, says Robert Colwell, a biogeographer at the University of Connecticut, Storrs. To begin with, the climate is warming much faster today than it ever did following the Last Glacial Maximum. The researchers also only included temperatures, not precipitation, in their climate maps, likely because ancient rainfall estimates remain shoddy, he adds. But if rains dry up at the same time that temperatures increase, moisture-loving amphibians would need to move even faster to survive. The team's data may be off, but "the qualitative result is likely going to hold up," Colwell says. The coming marches of many animals will likely dwarf what scientists like Sandel have seen following the waning of the Ice Age.

So, shrews and pikas, lace up those tennis shoes.