December 23, 2009 – Original Source: Scientific American
As global temperatures change, not all shifts will be equal. A new global analysis pinpoints the fast pace some species may have to move to remain in a suitable climate
Reports of maples on the march northward and butterflies flitting far afield are already flooding in, and climate scientists predict that with escalating temperature changes more species will need to either get out of dodge, or hope for emissions reductions that will help the planet dodge the climate bullet.
Much of Earth’s life forms are fine-tuned for specific ecosystems and their associated climates. Plunk a tree frog down in a harsh habitat it is not well adapted for, and it will fail to thrive—or even survive. Now, with regional climates shifting as a result of global warming, it is unclear just how far—and how fast—organisms will need to travel to keep up with moving climates. A new study, published online Wednesday in Nature, aims to paint a clearer picture by uncovering the variable velocity of climate shifts across the globe (Scientific American is part of Nature Publishing Group).
"A lot of people talk about the rate of climate change—but how far do you have to go to reach a new climate?" asks study leader Scott Loarie, a post-doctoral fellow at the Carnegie Institution in Stanford, Calif.
On average, given annual average temperature change models, local climates will move about 0.42 kilometers (or a quarter of a mile) each year, the study found. And 28.8 percent of the world’s biomes (or ecosystems, areas with similar climatic conditions) are facing rates of change more than 1 kilometer per year. "What we’re bringing attention to is the speed with which these things happen," Loarie says about the study, which analyzed these climate change velocities across the globe at the resolution of a single kilometer.
Although these shifts might sound like small beans for mobile animals like birds, which can pick their environment with relative precision, for the very small, the very large and the very rooted, such a pace might be impossible. "Plants might be particularly vulnerable" in the case of rapid local climate changes, says Dov Sax, an assistant professor of ecology and evolutionary biology at Brown University in Providence, R.I. And even species that can travel more easily, like butterflies, can be dependent on specific plants or other biome system members that are slower to follow temperature changes. If a species can move to more comfortable climes, "the right ecosystem needs to be there" for them to thrive, Sax explains.
Calculating climactic changes is a tricky business, and temperature is by no means the whole story. Loarie and his team chose temperature as a key marker, he says, because organisms are "bathed in temperature." His team also ran the models with predicted precipitation changes and arrived at similar conclusions, even though moisture levels can prompt more nuanced responses across species. Sax, who wasn’t involved in the study, notes that predicting how species will respond to these changes can be even more difficult. "We’re in a very early stage of figuring these things out," he says.
One of the more quantifiable aspects of this analysis, the Earth’s topography, turned out to play an important role in determining the velocity of these changes. "Slight differences in topography can have a big effect," Loarie says, noting that a species’ success might rest on the "difference between the north and the south slope."
There has been much hand wringing over mountainous plants and animals, which can only climb so high chasing cooler climes before they run out of real estate. In contrast, this study draws attention to the high velocity of change in flatland areas. Temperature and other climate changes in open expanses, such as the Amazon basin or Sahara Desert, will cover broader swaths of land than steep peaks, meaning that "large geographic displacements are required to change temperature appreciably," wrote the researchers. Thus, flatlandspecies will have to travel much farther than mountain-dwelling species to maintain their present-day temperature conditions—and with even less likelihood that the rest of their familiar biome will follow.
By contrast, with each kilometer up or down a mountain, climes can vary greatly. Thus, even some plant species may be able to keep pace with quick climate changes in the near future if they live in the right spot now. Loarie notes the importance of mountains to mitigate the effects of climate change, asserting that they "might provide real opportunities" for saving threatened species.
Certainly, even in areas with high velocities of climate change, each local organism has a particular range of conditions it can tolerate. "Some are going to be just fine where they are," says Sax. But others, he notes, "are going to need to track their climate" more closely, moving along with changes as they occur.
Rapid shifts in climate, however, are nothing new. As recently as the last glacial period, local climates and whole biomes shifted substantially—and in short order, forcing many species to move, adapt or die out. But despite earlier pollen analysis that pegged the movement of some tree species (that is, average advancement via seed dispersal) at about a kilometer per year after the last ice age, genetic studies have reduced that estimate to a pace closer to a tenth of a kilometer per year, Loarie says. Even if many species were able to roll with these ancient changes, he notes, "these [current] changes are happening so much faster—and that’s expressed in these velocities." Plants and animals are also contending with a much different landscape now than they were 12,500 years ago. "If we imagine plants and animals moving through a human-dominated area, it’s likely to be much slower," he says.
Those species that are capable of relocating at a brisk pace might indeed be thwarted by human development. Sax, who studies amphibian responses to climate change, says, "There are a lot of species you wouldn’t normally be concerned about that might be in trouble in the future" because a barrier stands between their current habitat and one they might need to occupy in coming decades. Species that will likely need to move north along the West Coast to stay cool, for example, may run into insurmountable urban obstacles like Los Angeles or San Francisco. "If there’s a city in the way, you’re just not going to be able to do it," Sax says about such species. And even in more rural areas, he notes, large expanses of crop monocultures like corn or soy could pose problems for organisms dependent more diverse natural habitats.
Even well-intended and successful protected areas might not be able to shelter all of their resident species indefinitely, note the study authors. Most of them are quite small and only some 8 percent of protected areas worldwide contain ample—and sufficiently variable—landscape to maintain their present climactic biomes 100 years from now. The best hope will be for areas with a range of lands to for species move onto. "If you have a preserve that currently features a bunch of different kinds of climates," says Loarie, "that preserve will be much more robust—kind of like a diverse stock portfolio."
Expanding preserves and creating more connections among them will be increasingly important, as "we’d expect species to have the most difficulty moving outside of protected areas," Loarie says. And for instances where plants or animals don’t seem to be adjusting, "assisted migration might be an important component," he says, although he and Sax note that the implications of this practice are not well understood and can be quite risky.
The best strategies, Loarie says, will be those with a two-pronged approach—those that slow climate change and expand viable habitats. He points to mitigation efforts discussed at Copenhagen, such as REDD (reduced emissions from forest deforestation and forest degradation), which would encourage forest preservation, thereby both helping to put the brakes on carbon dioxide levels and providing more room for many species to move—a plan he calls a "win-win situation."
On a smaller scale, individuals can lend struggling species a hand by going native, Loarie says. Giving climate-challenged creatures a better toehold "could be as simple as people planting native plants in their garden because native plants attract native pollinators," he explains. The key, he says, "is keeping the landscape connected," so that when species need to hit the road, they have a throughway—or at least a possible path.