Hit & Run

As Planet Heats Up Critters Are Moving Poleward and Uphill

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This pika is moving on up.

A new study published in the current issue of Science reviewed the data from 54 scentific papers that mapped the habitat ranges of more than 2,000 species. As ScienceNow reports

On average, the team finds, creatures move both up mountains and farther away from the equator at a speed that keeps pace with the rate of climate change and at a pace that is far faster than previously predicted. …

The new study has plenty of limitations, [Chris] Thomas Chris [of the University of York in the United Kingdom] acknowledges. The scarcity of papers meant that most of those included targeted only Europe and North America, few were from the Southern Hemisphere, and no marine species were included. "We're prisoners of the data," he says. But by analyzing 54 papers that met their criteria, the researchers found that, on average, organisms move up hills at 12.2 meters per decade, twice the rate previously described in the literature. And they move away from the equator at 17.6 kilometers per decade, which is three times the rate previously described.

The researchers also calculated how far a species would have to move in a given region of the world to stay at the same temperature. The actual migration rates, on average, closely follow the rate of warming year by year in that region—strong evidence, the researchers say in their paper published in Science today, of a direct link to climate change.

Thomas was surprised that the species moved so fast over ground, where they have to move 50 to 60 kilometers on average to find a habitat 0.5°C cooler. "That's quite a long distance across human-dominated landscapes," he points out. In addition, he had assumed that the uphill rate would be faster, where species need to move less than 100 meters to drop 0.5°C, but the uphill migration rate was slower, a finding the researchers can't explain. Either species are now stuck on tops of mountains, Thomas speculates, or those in the Northern Hemisphere might be moving around mountains laterally to the colder north face.

Sifting through the data, the authors were also surprised to find there was no difference between taxonomic groups: plants move at the same rate as insects, and birds are no faster than mammals. But when they looked at individual species, they found that within these taxonomic groups, some species move much faster than others, such as the comma butterfly, which moved northward 220 kilometers in 2 decades. And 22% of species, including the Cirl bunting, even move in the opposite direction toward warmer temperatures, suggesting that they are more flexible to changing climates than others, Thomas says.

This is not the first time the movement of species has been cited as evidence for climate change. For example, back in 1974, Time magazine in its article "Another Ice Age?" cited reports that armadillos were retreating toward the south as evidence for global cooling. There had actually been a bit of cooling between the 1940s and 1970s, so it's no wonder armadillos headed south. 

This new study adds to the balance of the evidence that the planet has been warming in recent decades. If, as some skeptics assert, greenhouse gases are not significantly implicated in the recent warming, then they must convincingly supply other mechanisms for producing the increasing temperatures. As much as I would rather it not be the case, in my judgement, the skeptics have not yet done so. But the good news is that empirical data could well settle the question of whether or not climate computer model projections are accurate.