"Polar bears have become an icon for species threatened by climate change, and justifiably so; at the high latitudes of their home, climate-change projections show very large changes in temperature relative to lower latitudes," Tim Bonebrake of Stanford University, US, told environmentalresearchweb. "Our study demonstrates how incorporating other critical variables (e.g. precipitation and adaptation to climatic variability) indicates that polar bears may not be the only species threatened by climate change; lower latitude and tropical species could face equally significant challenges under future climatic regimes."

Because temperatures are fairly constant throughout the year, species in the tropics are often better adapted to coping with variations in precipitation than a wide range of temperatures.

"We applied the adaptive evolutionary model to global climate data to quantify the effects of variability in both temperature and precipitation for species throughout tropical and temperate ecosystems," said Bonebrake. "In other words, if a species is adapted to seasons of wet and dry vs. hot and cold, how will that affect its ability to respond to climatic changes?"

The results indicated that warming caused the greatest change in fitness at the tropics because of tropical organisms' reduced ability to cope with a broad range of temperatures. Precipitation changes tended to have the most impact in high-latitude northern regions and the smallest effect in high-latitude southern regions. Northern high latitudes experience relatively constant precipitation year-round while climate change is projected to bring large effects on rain and snowfall.

To date there has been little research into how changes in precipitation will affect wildlife; in any case, the projections for precipitation are less reliable than those for temperature.

By examining predicted changes in the year-to-year variability of temperature and precipitation, Bonebrake and colleague Michael Mastrandrea discovered that the magnitude of climate-change impacts could vary much more with latitude than previously believed. Indeed, some tropical regions may be even more affected than temperate areas.

"Our regional mapping of climate-change impacts shows diverse responses across latitude," said Bonebrake. "Based on adaptation to seasonal variability in precipitation and temperature and the projected changes in precipitation and temperature, as well as projected changes in the variability of temperature and precipitation, the regions of the highest projected climate-change impacts are at high and low latitudes."

The team's evolutionary regional climate-change index predicted that the Mediterranean and southern equatorial Africa would be hardest hit, while Central America, northern Europe, north-eastern Europe, South-East Asia and West Africa are also likely to be highly impacted.

"The model used in this study has a number of assumptions and hypotheses that need to be field tested," said Bonebrake. "Research is currently underway in the field in North and Central America to explore how species, in this case butterflies, adapt to tropical and temperate climates."

The researchers reported their work in PNAS.