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And many scientists expect that trend to continue. According to Intergovernmental Panel on Climate Change reports, air temperature is expected to continue warming globally from 1.4 to 5.8 degrees Celsius during the 21st century.

Now, scientists are looking at those that will be most affected by the effects of climate change in Rocky Mountain ecosystems -- wildlife.

Three studies funded by the U.S. Geological Survey are under way to examine how global warming may affect the habitats of native fish, ungulate species and grizzly bears. The goal of the studies is to provide tools that will help wildlife managers predict climate change-induced impacts on wildlife throughout the Rocky Mountains and the interior western United States.

Fish species

State and federal agencies, as well as nonprofit groups, are increasingly consumed with the recovery and restoration of native trout and salmon throughout the western United States. Almost all of the native inland cutthroat species, grayling and bull trout have been proposed for listing under the Endangered Species Act, and a number are currently listed as "threatened."

Trout, grayling and char historically inhabited a variety of freshwater habitats, but their populations have declined due to habitat degradation, fragmentation and introduction of non-native species. The remaining intact populations of native trout, char and grayling species are largely restricted to small, fragmented headwater habitats. Recent localized extinctions of these small populations caused by wildfires and subsequent floods have highlighted their vulnerability.

"Fishes are excellent indicators of changes in environmental conditions because they're ectotherms, meaning their external environment regulates their temperature," said Clint Muhlfeld, a USGS aquatic ecologist.

Complicating this situation is global climate change, which is likely to increase air and water temperatures and the risk of catastrophic fire, change the timing and quantity of water from snowpack, increase winter flooding in some areas and provide habitat conditions that favor introduced species.

Because of this, USGS researchers have joined with the Forest Service and Trout Unlimited to look at how global warming may drive landscape-scale impacts that affect the freshwater habitats of key native fish species, including several subspecies of cutthroat trout, bull trout and arctic grayling.

The team will examine the geographic distribution of target species and populations in relationship to current temperature and flow regimes. Using these data, the project will create a model to predict how changes in climate will affect native salmonid distributions across the western United States and which habitats and populations will be affected the most, based on expected changes in flows and temperatures.

The results of the project are expected to be published in a scientific journal and distributed through a series of workshops and meetings with resource managers.

"We're predicting that as global climate change continues and we see a warming trend, these trout will start to lose suitable habitat in lower elevation areas and seek refuge in [higher-elevation] headwater systems," Muhlfeld said.

The study has received $230,000 in funding for this year, but Muhlfeld hopes to continue the research to examine effects in specific ecosystems such as the Flathead River system in Glacier National Park and to develop a framework to guide resource managers on the best ways to conserve native fish.

Ungulate species

The ecology of hoofed big-game species in the northern Rocky Mountains, known as ungulates, is strongly influenced by climate. Climate change affects summer precipitation, winter snowpack and the timing of spring, all of which determine animal physiology, demography, diet, habitat selection and predator-prey interactions. But the degree of response to these impacts from animals such as elk, moose, mule deer and pronghorn antelope is uncertain.

In the northern Rocky Mountains, ungulates are managed by state and federal agencies, and funding of management programs is supported by the sale of hunting licenses and other tourism-related activities such as fishing licenses and campground fees. Thus, impacts of climate change not only directly affect ungulate species, but also impair the ability of managers to promote conservation through hunting and tourism -- a significant hit to the economies of many Western states.

To determine how global climate change may affect ungulate species, scientists from USGS, the University of Wyoming, Pennsylvania State University and Humboldt State University will look at how climate change-induced events such as decreased snowpack, early spring conditions and increased drought may alter species' migration routes and population numbers, influence disease prevalence such as brucellosis in feed grounds and affect the abundance of vegetation such as aspen.

Vegetation data will be compared within and between years, correlated with weather station data and tested to see whether it affects the timing of ungulate movement between winter range or feed grounds and summer range. The researchers will look at data on snow levels in the southern Greater Yellowstone Ecosystem for a potential influence on animal movement and vegetation productivity. The team will also use population models for five species of ungulates across Wyoming to summarize existing data and forecast potential impacts of climate change.

The long-term goal of the project is to provide natural resource managers with tools to understand how climate change will affect various ungulate species in the region.

Grizzly bears

The final study that USGS is working on in the northern Rockies is focused on the effects climate change has on grizzly bears. Using data from a long-term telemetry study that dates back to 1973, researchers hope to determine whether there is a relationship between changes in temperature and bears' denning habits.

"With global climate change, we're seeing longer falls and warmer temperatures extend later into the season," explained USGS wildlife biologist Chuck Schwartz. "Are bears responding to that by staying out of their dens or not?"

Schwartz emphasized that researchers will not be able to determine whether there is a cause-and-effect relationship between warmer temperatures and bears' denning habits, but only whether there is a correlation between the two.

Nevertheless, the study's findings could have important implications for the recovery of grizzly bears, since bears' survival rates are very high while they're secure in their dens. However, the more time they spend outside their dens, the greater the risk of mortality.

Many grizzly bear deaths occur during the hunting season, when hunters, afraid for their lives, shoot the bears. So, if grizzly bears start spending less time in hibernation, it could also mean increased conflicts between people and bears.

Schwartz expects to start analyzing data from the telemetry study -- which has typically involved 50 to 75 radio-collared bears in the last decade -- this winter and plans to release the results next spring. The study has received $30,000 in funding from USGS.

"We don't have the ability to reverse climate change ourselves, obviously," Schwartz said, "but the additional information [from this study] adds to the database of scientific knowledge about the impact, or the potential impact, assuming we find one, of climate change on wildlife species and what that might mean for humans and bears and what activities managers might employ try to minimize conflicts between bears and people."

Gable is an independent energy and environmental writer in Woodland Park, Colo.

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