Study: Animals feel heat of climate change

Researchers braving Greenland's frigid temperatures and tempestuous snowstorms have collected the first direct evidence that a change in the wind can alter identically the fate of diverse animal species living vast distances apart.

They observed the powerful influence of shifting climate on herds of caribou and musk oxen, separated by an impenetrable 600-mile glacial sheet that splits the world's largest island. The locale's special natural features made it an ideal setting for the unique study.

The survey of the massive mammals -- living relics from the last Ice Age long adapted to breeding in sub-zero harshness -- illustrates how Arctic species sensitive to the effects of changes in Earth's weather patterns can serve as an early warning signal for the rest of the planet, the investigators said.

"Here we have a very simple system with a very clear signal: two species on opposite sides of a continent that never mix, never compete for food and have no common predators, yet their population dynamics are synchronized," said Eric Post, assistant professor of biology at The Pennsylvania State University in University Park.

"The only thing they have in common is the large-scale climate system that influences weather throughout the Northern Hemisphere."

Fluctuations in that system and the ups and downs of the animal populations occur in sync, Post found with his co-author, Mads Forchhammer, associate professor of population ecology at the University of Copenhagen in Denmark. Their report will be published in the Nov. 14 issue of the British journal Nature.

"It's been a fairly big question why many Northern Hemisphere mammals follow the same cycles in population abundance across vast areas," said John Stachowicz, assistant professor of evolution and ecology at the University of California, Davis.

"Why they should all cycle synchronously is a much bigger question," he added.

"It's tempting to say climate, but others have pointed out that dispersal, a common resource base, wide-ranging predators, et cetera, could all produce the same synchrony," Stachowicz told United Press International. "This study does a fantastic job ... of really showing that the only possible connection between these populations is via climate."

The investigators compared long-term data on a major weather system called North Atlantic Oscillation with records of the rise and fall in the number of caribou and musk oxen roaming their home turf over a 21-year period.

"Focusing on the long-term population dynamics of caribou and musk-oxen data we had collected from various hunting and observational statistics," Forchhammer told UPI, "we found that both species' dynamics were influenced by one of the most prominent large-scale climate system in the Northern Hemisphere, the North Atlantic Oscillation."

The system -- a smaller, less-known Nordic cousin of El Nino -- causes atmospheric pressure to seesaw between regions, affecting winter weather in Greenland and much of the Northern Hemisphere.

"The North Atlantic Oscillation can be pictured as a fluctuating pressure corridor that squeezes and channels the westerly winds between North America and northern Europe, influencing the direction and speed of the winds and affecting temperature and precipitation on both sides of the North Atlantic Ocean," Post explained.

To gauge the large-scale system's influence on local conditions, the researchers compared Greenland weather reports with the so-called NAO index, a measure of the North Atlantic Oscillation dating back to 1864. Then, they looked at the population picture for each herd over the same period.

"We found that whenever the NAO had an approximately equal effect on the population dynamics of two herds, these fluctuations were more synchronized, even though the herds were on opposite sides of the subcontinent of Greenland," Post said.

Likewise, whenever the NAO exerted opposite effects on them, the two species fell out of sync so that when one was thriving, the other was thinning.

"Because the work shows how pervasive are the responses of populations to climate, it underscores the importance of reducing the rate of emission of climate-altering carbon dioxide and other contributors to global warming," John Harte, professor of energy and resources at the University of California, Berkeley, told UPI.

The team is conducting field work to find out exactly how climate drives the animal populations.

"Remember, these are two of the few large mammals that survived the last period of rapid warming in the Northern Hemisphere, at the end of the Pleistocene (about 10,000 years ago)," Post told UPI.

"They're relics, adapted to much colder and drier conditions than are predicted to develop in the far north over the next century. Will they make it? Maybe, but the chances of all of these populations persisting is greatly reduced by their tendency to be synchronized by large-scale climate."

About 125,000 musk oxen inhabit Canada, Greenland, the polar regions, Alaska and Norway. The primitive animal -- which derives its name from the musk scent that its facial gland emits during breeding season -- resembles a small bison. Its enormous shaggy head is crowned by pigtail-shaped horns. Its coat is trimmed with hair that can grow to 6 feet in length, a record for a non-human animal.

The world's 5 million caribou dwell in the Arctic tundra, mountain tundra and northern forests of North America, Russia and Scandinavia. The species comes in five varieties, including the familiar domesticated European kind known as reindeer. The bulls sport immense, velvety, multi-pronged antlers that turn them into favorite targets of hunters.

The animals' changing hooves shift with the season -- in the winter growing horny edges that help them navigate snow and ice and in the summer softening their soles to facilitate stepping on rocks and pebbles.

Both species prefer vegetarian fare, face their greatest natural predatory threat from wolves and give birth to single offspring.

The investigators braved hazardous conditions to learn more about the animals.

"The winter campaigns were the roughest because we had to cope with extreme weather, such as minus 45 degrees Celsius (minus 49 degrees Fahrenheit) and snowstorms, and still ensure the collection of data," Forchhammer recalled.

"Admittedly, during these dark and cold periods, I often asked myself whether it really was worth the effort. Why not focus on species living under benign weather conditions?" he said.

"Then again," he added, "the payback in terms of unique data" and the "extraordinary and beautiful" scenery outweighed those problems.

Other scientists agreed the results were worth the price.

"What makes this study interesting is that it offers a pretty rare real-world look at something we have only known from mathematical models," Gareth Russell of the Ecology, Evolution and Environmental Biology Department at Columbia University in New York City said in a telephone interview.

The research points to the need to combine data from studies made in widely separated areas, said Fred Adler, associate professor of mathematics and biology at the University of Utah in Salt Lake City.

"Such combinations could have more power to detect the incipient effects of climate change than tracking a single region alone," he told UPI.

As a result of the findings, other scientists could begin looking at the effect of large-scale climate systems on the animals they study, the researchers said.

"What does this tell us about the potential ecological consequences of future climate change?" Post asked. "At the very least, it should make us wonder whether climate trends might bring into synchrony the ups and downs of populations of species that currently are fluctuating independently."