CHANGE IN THE AIR: FOURTH IN AN OCCASIONAL SERIES ABOUT HIGH-ALTITUDE RESEARCH IN COLORADO

CRESTED BUTTE - Physicist-turned-ecologist John Harte says he's glimpsed the future of Colorado's high country under global warming, and it's not a pretty sight.

Sagebrush will drive out wildflowers as the state's prized alpine meadows dry up, the ski industry will founder within 50 years, and property values in mountain resort towns will plummet, Harte predicts.

The Berkeley, Calif., researcher has spent the past 14 years using electric heaters to simulate a warmer world on a hillside meadow at 9,600 feet in Gothic. The former mining town is several miles north of Crested Butte, designated the Wildflower Capital of Colorado by the state legislature.

Harte's climate-manipulation experiment was the first to use overhead heaters to mimic some of the expected effects of global warming on a natural ecosystem. The heaters have been operating continuously - 24 hours a day, year-round - since January 1991.

"Places like this will look much more like the sagebrush meadows around Gunnison," Harte said during a visit to his research plots at the Rocky Mountain Biological Laboratory in Gothic.

"We're talking about a completely different future for this region," Harte said as he hiked up a hillside cloaked in a riotous, multihued tangle of blooming wildflowers. "I hope I'm wrong."

Some climatologists and Colorado ski industry officials dismiss Harte's bleak outlook. And the folks at the Crested Butte Wildflower Festival aren't rushing to rename the event in honor of the hardy sagebrush shrub.

But key findings of Harte's federally funded meadow experiment - earlier springtime snowmelt, drier summer soils and sagebrush encroachment into alpine meadows - are viewed as likely scenarios in several studies of the potential impacts of global warming on the Rocky Mountain region.

The most comprehensive study to date is the 240-page Rocky Mountain/Great Basin Regional Climate-Change Assessment, prepared for the U.S. government. More than 125 researchers - including climatologists, hydrologists and ecologists - contributed to the report.

In it, scientists looked at the likely impacts of various future climate scenarios, based largely on the projections of two computerized climate simulations called general circulation models.

Both models predicted a surge in regional temperatures that would trigger transforming changes by 2100. The impacts, according to the study's authors, could plausibly include:

• Big reductions in the mountain snowpacks that provide most of the region's water. As temperatures increase, fall and early winter precipitation will likely continue as rain later in the year. Spring melting would start earlier.

"Marked temperature rise and winter precipitation changing to rain would likely reduce the magnitude and season length of snowpacks, even to the point of eliminating them" in some parts of the Rocky Mountain/Great Basin region.

• Significant summer drying and reduced soil moisture in Colorado's mountain forests, along with lower summer flows in rivers and streams. "Only those (plant) species that could disperse upward in elevation will be able to secure the necessary cooler, wetter conditions . . . Some native species would be lost."

• An earlier wildfire season, more droughts, more large-scale insect outbreaks in forests.

• Reduced habitat for native cold-water fish such as the cutthroat trout. The problem would be exacerbated by competition from nonnative fish species, which typically can tolerate higher temperatures.

"There is a distinct prospect of extinction among some cold-water endemic fish species which are already threatened or endangered."

• Shorter ski seasons and a higher snow line, placing low-elevation resorts at risk. "All analyses based on significantly higher temperatures project reduction or disappearance of skiing" in the region, according to the report.

Glimpse of warmer world

During the 20th century, the global average surface temperature increased about a degree, according to the Intergovernmental Panel on Climate Change.

The panel was established by the World Meteorological Organization and the United Nations in 1988. Hundreds of researchers around the world contribute to its periodic assessments.

Some of the 20th century warming probably was due to natural climate variability. But most of the observed warming in the past 50 years likely occurred because of the human-caused increase in heat-trapping "greenhouse" gases such as carbon dioxide, the climate panel concluded in 2001.

Later that year, a National Academy of Sciences report endorsed that intergovernmental panel finding, saying that it "accurately reflects the current thinking of the scientific community on this issue."

"Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise," according to the academy report, requested by the White House.

"Human-induced warming and associated sea level rises are expected to continue through the 21st century," the panel wrote.

Historian Naomi Oreskes analyzed more than 900 climate-related research papers published in peer-reviewed scientific journals between 1993 and 2003. She summarized her findings late last year in the journal Science.

"There is a scientific consensus on the reality of anthropogenic (human caused) climate change," the University of California at San Diego researcher wrote. "Climate scientists have repeatedly tried to make this clear. It is time for the rest of us to listen."

The world is warming.

And Colorado has not escaped the trend.

The state's average annual temperature increased 1.5 degrees during the past century, according to research meteorologist Martin Hoerling of the Climate Diagnostics Center in Boulder.

Six of Colorado's 10 warmest years occurred since 1981, according to temperature records from the National Climatic Data Center.

If atmospheric levels of carbon dioxide and other heat-trapping greenhouse gases continue to increase as projected - due mainly to the burning of fossil fuels - the planet is expected to warm another 2.5 to 10.4 degrees by 2100, according to the Intergovernmental Panel on Climate Change.

Most continents would warm more rapidly than the global average. North America could see warming in the range of 6.3 to 13.5 degrees by 2100 under high-emissions scenarios, according to panel.

The two computer models used in the 2003 Rocky Mountains/Great Basin assessment, known informally as the Hadley and the Canadian models, projected regional warming of 4.5 to 14.4 degrees by 2100.

More up-to-date models now call for somewhat less Western warming by century's end - somewhere in the range of 3.6 to 10.8 degrees, said Daniel Cayan, director of the climate research division at Scripps Institution of Oceanography in La Jolla, Calif.

But some scientists view these climate projections as little more than high-tech guesswork. One prominent critic once compared general circulation models to Ouija boards.

Colorado State Climatologist Roger Pielke Sr. says the models are incomplete and unreliable, especially when used to forecast climate change at the regional level.

"My feeling is that the climate system is so complex that we can't predict with skill what will happen in the future," Pielke said.

"There's general acceptance that humans are altering the climate system," he said. "And I think we should probably control CO2 (carbon dioxide). But to try to base it on these models is not solid. It's not good science.

"This report grossly overstates our ability to confidently predict regional climate change and therefore the impacts that are inferred from that," Pielke said of the Rocky Mountain/Great Basin regional assessment. "It gives the illusion of authority and scientific accuracy."

Utah State University ecologist Frederic Wagner, co-coordinator of the regional assessment, called Pielke a maverick who is "almost ideologically committed" to criticizing global climate models.

"I think he's irrational on this whole subject," Wagner said. "I know he's a man with some credentials and qualifications, but I don't know anybody else who takes the stand that Pielke does."

In response, Pielke pointed to a November 2001 policy statement on climate change from the American Association of State Climatologists. "Climate predictions have not demonstrated skill in projecting future variability and changes in such important climate conditions as growing season, drought, flood-producing rainfall, heat waves, tropical cyclones and winter storms," it states in part.

Big changes on horizon

Boulder climatologist Linda Mearns served on the six-person Assessment Team that oversaw the Rocky Mountain/Great Basin report.

Mearns is a senior scientist at the National Center for Atmospheric Research, known as NCAR. She is a lead author of two chapters in the next intergovernmental panel assessments, scheduled for publication in 2007.

Climate models are not crystal balls. The scenarios outlined in the regional assessment present a range of "plausible futures," not hard-and-fast predictions, she said.

"I wouldn't necessarily disagree with Roger that we really don't know the details about what will happen, let's say, in the Front Range," Mearns said. "It's true. We don't know the details . . . But that doesn't mean we know nothing."

Astronomers don't need the Hubble Space Telescope to see giant craters on the moon's surface. And climate modelers don't need to resolve the finest regional details to spot some of the big changes on the horizon, Mearns said.

If the explosive increase in heat-trapping greenhouse gases continues unchecked, warming will accelerate, leading to far-reaching changes in the Colorado Rockies, she said.

The climate models, despite their shortcomings, help researchers and potentially affected parties - water managers, foresters, fisheries, farmers and ranchers, ski industry officials and others - explore the range of potential impacts, Mearns said.

Critical snowpack at risk

The Rocky Mountain/Great Basin region was home to eight of the nation's 10 fastest-growing states between 1995 and 2000. Colorado's current population of 4.6 million is expected to swell to 7.2 million by 2030, a 56.5 percent increase.

Residents in this region, which ranges from semi-arid to arid, derive 85 percent of their water from surface sources, and 85 percent of that surface water comes from snowpack runoff.

Any climate changes affecting either water availability or the timing of snowmelt runoff could have profound social, economic and ecological repercussions.

And the ripple effects would be felt far beyond the Rockies and the Great Basin. Snowpacks in the region form the headwaters of the Columbia, Missouri, Colorado, Rio Grande, Platte and Arkansas rivers, providing water for millions of people living hundreds of miles downstream.

Western snowpacks are expected to decrease as the climate warms - even though some models forecast a slight increase in annual precipitation - for two reasons.

First, warmer temperatures will result in more of the the precipitation falling as rain rather than snow, pushing the snow line higher. Second, the snowpack will develop later in the year and melt earlier in the spring, according to Climate Change Impacts on the United States, a 2000 report from the U.S. Global Change Research Program.

Denver climatologist Gregory McCabe was the lead author of a snowpack study cited in that 2000 report, which is known as the national assessment. McCabe and colleague David Wolock used the Hadley and Canadian computer models to examine likely changes in snowpack in the Rockies, the Sierra Nevada and the Pacific Northwest by 2100.

The models suggested that the Southern Rockies, including southern Colorado, could see a 55 to 98 percent reduction in April 1 snowpack by 2100.

The outlook for the Central Rockies, including the northern Colorado mountains, was less clear. One model showed no significant snowpack change, while the other pointed to a 75 percent reduction.

But like Pielke, McCabe questions the reliability of forecasts based on global climate models.

"They show some pretty drastic changes, but you have to realize that there's a lot of uncertainty with those projections," said McCabe, a U.S. Geological Survey scientist.

Altering water resources

As the snowpack shrinks, peak runoff will arrive earlier and earlier. Winter and early spring floods could become more common, straining reservoir capacity in the West at a time when public antipathy to building dams makes the construction of new ones "an unlikely solution," according to the regional assessment.

Denver Water serves 1.2 million customers. The utility draws roughly half its water from the South Platte River watershed and half from the headwaters of the Colorado River.

It relies on a network of pipelines, canals and reservoirs to transport and store mountain runoff.

If climate change causes snowmelt to run off the mountains earlier and quicker than it does today, the flows could overwhelm those canals and pipelines, said Marc Waage, a water resource engineer at Denver Water.

"We'd lose water that we would be able to deliver today because the snow now melts at a slower rate," Waage said.

A shift to an earlier runoff peak could also throw a monkey wrench into the state's Byzantine water-rights system, which is based on the assumption of a static climate.

"There are water-right decrees with fixed dates in them for when they can start to divert water out of the river or put that water into storage," Waage said. "If the whole runoff cycle is shifted earlier in the year, how will the administration of these water rights be affected?"

Next year, Denver Water will update its Integrated Resources Plan, the utility's long-range water supply and conservation document. For the first time, it will include an assessment of the possible effects of climate change on the Denver Water system.

"We're quite concerned about it," Waage said.

"We've already got our hands full with trying to provide enough water to the region to keep up with population growth," he said. "To add the additional problem of climate change just exacerbates an already difficult situation."

Earlier spring runoff

Reduced snowpacks and an earlier peak in springtime runoff have already been observed in some parts of the West, most notably in the Pacific Northwest and lower elevations in California's Sierra Nevada. But it is unclear if those changes, which span several decades, are tied to natural climate variability or greenhouse-induced warming, the Scripps Institution's Cayan said.

In Colorado, statewide April 1 snowpacks have been below average 14 of the last 19 years. But again, natural climate variability could explain it.

In general, the higher altitudes and colder temperatures of the Colorado Rockies should provide a buffer against some of the snowpack and runoff changes.

For now.

But in a 2004 paper in the journal Climatic Change, California climatologists used computer models to look at likely future changes in the timing of snowmelt runoff in western North America.

The biggest shifts are expected in the Pacific Northwest, the Sierra Nevada and the Rocky Mountains, according to the paper by Iris Stewart and two colleagues, Michael Dettinger and Cayan.

In the Colorado Rockies, springtime runoff is expected to peak two to five weeks earlier by 2100, according to the study.

An earlier runoff peak would result in lower summer flows. That means less water for fish as well as urban lawns and irrigated farmland. Agriculture uses about 80 percent of Western water and relies heavily on summer irrigation.

More rain would help, but that doesn't appear to be in the cards.

The two computer models used in the Rocky Mountain/Great Basin regional assessment did, in fact, call for big annual increases in precipitation - a jump of anywhere from 54 to 184 percent.

But most of the current models show little or no change in annual precipitation for the West in the coming century, Cayan said.

For example, the latest National Center for Atmospheric Research model calls for a "slight annual increase" in precipitation over the Colorado Rockies by 2100, said Gerald Meehl, a senior scientist at the Boulder lab.

Experts say river and stream levels could drop in the summer even if the Western climate gets a bit wetter.

How is that possible?

Higher temperatures will evaporate more water, negating the effects of any extra rain in all but the wettest scenarios.

In a study of the Colorado River Basin, California researchers Peter Gleick and Linda Nash calculated that if temperatures warm 7.2 degrees, a 15 to 20 percent annual precipitation increase would be needed just to maintain current streamflow levels, due to losses from evaporation.

Threat to meadows

In the high country, alpine meadows and tundra will be among the ecosystems most vulnerable to future warming, according to several key reports:

• Rocky Mountain meadows are "likely to face extreme stress and disappear in some places," said one assessment.

• "Unique natural systems such as prairie wetlands, alpine tundra and cold-water ecosystems will be at risk, and effective adaptation is unlikely," according to another.

"Effective adaptation is unlikely" is another way of saying that mountaintop tundra will vanish because it cannot migrate to higher altitudes to escape warming.

On Colorado's highest peaks, the alpine tundra community is a ground-hugging mix of grasses, sedge, wildflowers and other forbs, moss, lichen and low shrubs such as dwarf willow and birch.

In general, the trees in Colorado's mountain forests are expected to shift to higher elevations as the climate warms.

As the tree line moves up, much of the state's tundra is expected to disappear, said Ron Neilson, a U.S. Forest Service bioclimatologist who uses computer models to study likely vegetation changes in a warming world.

"Basically, the forests go off the top of the mountains," Neilson said.

Park subject to change

Colorado State University researchers estimated that the tree line in Rocky Mountain National Park could rise 244 feet for every degree of warming. At that rate, 5 degrees of warming would force the tree line 1,220 feet higher.

The park, which draws about 3 million visitors each year, straddles the Continental Divide and boasts more than 110 peaks higher than 10,000 feet. More than 100 square miles of the park lie above timberline - a stark landscape of rock, ice and alpine tundra.

According to CSU estimates, a 3.6-degree rise would eliminate about 20 percent of the park's tundra. More than half of it would disappear if the climate warms by 5.4 degrees, and all of it would vanish if the temperature climbs 9 to 10.8 degrees.

The tree-line shifts would likely occur over several centuries. Long before the conifers completed their upslope march, the tundra would be invaded from below by grasses and other rapidly colonizing plants, according to the Colorado State study.

But U.S. Geological Survey ecologist Thomas Stohlgren, co-coordinator of the Rocky Mountain/Great Basin regional assessment, rejects the vanishing tundra scenarios.

"The tundra isn't going to disappear," he said. "The extent might change, but it will survive.

"There are some really big believers in rapid change, and there are others who believe that it might not be so rapid, or that there might be some mitigating circumstances," he said.

"I'm in the latter group. I'm in the group that believes there is more uncertainty."

The Rocky Mountain National Park study concluded that warming would harm creatures that rely on tundra, such as the white-tailed ptarmigan. Yellow-bellied marmots and pikas also could be impacted.

At lower elevations, warmer temperatures would likely reduce winter mortality among young elk in the park, exacerbating an existing overpopulation problem. Aspen, willow and other elk foods would likely suffer.

The Colorado State-led study said warming could help efforts to boost the number of native greenback cutthroat trout in the park's waters, allowing them to spawn earlier and in streams that currently are too cold for breeding.

But the authors of the Rocky Mountain/Great Basin report concluded that, regionwide, warming is likely to reduce habitat available to cold-water fish such as trout. Warm-water species such as minnows and suckers would likely benefit.

The lynx and the Uncompahgre fritillary butterfly are two other Colorado-dwelling creatures considered especially sensitive to climate warming.

Sagebrush future?

Below the tundra, in Colorado's high-elevation forests, alpine meadows could face threats from shrubs creeping upslope. Warmer, drier summers would favor the upward expansion of shrubby plants with tap roots that can probe for deep soil moisture.

Such as sagebrush.

Because shrubs like sagebrush have much shorter life spans than most trees, sagebrush encroachment could occur relatively quickly, serving as one of the "early indicators of climate change" in the region, according to the regional assessment.

Which brings us back to John Harte, a professor of environmental science at the University of California at Berkeley, and his experimental Gothic plots.

For 14 years, Harte has continuously warmed five 330-square-foot plots, resulting in a 3- to 4-degree increase in soil temperature. That's roughly what would be expected by 2040, he says, if current trends in the emission of heat-trapping greenhouse gases continue.

Five nearby control plots remain unheated.

The meadow project is funded by the National Science Foundation, which pays the $300 monthly electricity bill, among other things.

In the heated plots, spring snows melt up to two weeks earlier than in the control plots, Harte explained to a visitor last summer. Soils near the surface are drier, favoring deep-rooted plants.

Wildflowers - the Crested Butte area has more than 100 species of them - generally have shallow roots and have not fared well in Harte's plots.

The result: Sagebrush is taking over the heated plots.

"At some point, we're going to lose the diversity of wildflowers we see in the meadows" around Colorado mountain resort towns like Crested Butte, Vail, Aspen and Telluride, said University of Maryland ecologist David Inouye.

Inouye has monitored the blooming of Gothic-area wildflowers each year since 1973, when he first visited the Rocky Mountain Biological Laboratory as a graduate student.

"This place may become a base camp for people working at higher altitudes, where the wildflowers have shifted up to," Inouye said while checking one of his monitoring plots near the Gothic lab last summer.

"The meadows may shift up until they reach the top of the mountain and get pushed off the mountain and disappear.

"So I enjoy it while I can. Because it may not last."

Story by Jim Erickson • Photos by Judy Walgren • Rocky Mountain News

ericksonj@RockyMountainNews.com or 303-892-5129

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