Over the past few decades, the Earth's rising temperatures have slowly shifted the climate in many areas. That would be expected to cause species to shift in response, and a variety of studies have suggested they are. (You can see this clearly at the US Arbor Day Foundation, which has an animated map showing changes in plant habitats.) But most of these studies have looked at a limited number of species or a narrow geographic region, making it hard to put together a clear picture of global trends. Now, a study has combined a lot of the individual ones into a meta-analysis, and finds that species are shifting habitat faster than we had assumed, but aren't all moving towards cooler climes.

The authors looked at two classes of studies, ones that focused on changes in altitude (plants and animals moving uphill) and others that focused on changes in latitude, as species respond to a warming world by moving towards the poles. Although the result is a bit more global, it's still heavily biased towards Europe and North America (with Chile and Malaysia also making appearances). Still, the studies are enough to include over 1,300 species, which the authors consider in 23 distinct groups, divided by taxonomy and geography (in the authors' example, plants in Switzerland).

The mean travel poleward of all the species included in these studies was 17km a decade; vertically, the mean had a species moving 11m uphill. That's not especially speedy, but it's still two to three times faster than previous estimates had placed on these values. And over several decades, those kilometers can add up. Perhaps more significantly, two different tests indicated that species were moving the fastest in areas that are experiencing greater temperature changes.

The type of species involved doesn't seem to matter at all. "Much greater variation is associated with differences among species within a taxonomic group than between taxonomic groups," according to the authors, who note that bird species, which are relatively mobile horizontally, haven't tended to shift their habitats as much vertically. And over 20 percent of the species actually moved in a direction opposite from the one that would be predicted to be due to a warming climate. So, things are changing on average, but the details may vary considerably.

The authors point out that there are a lot of reasons some species may respond in a manner different from the average—everything from physiological differences to habitat fragmentation may play a role. Still, the study provides another indication that we don't have to look to any temperature gauges to see signs of a warming world.

Science, 2011. DOI: 10.1126/science.1206432 (About DOIs).