In Rockies Meadow, Early Spring Gives Some Experts Chills

John Roach
for National Geographic News

April 11, 2005

For nearly three decades scientists have carefully watched a Rocky
Mountain meadow spring to life.

The meadow is nestled at about 9,500 feet (2,900 meters) above sea level between towering, snowcapped peaks a few miles outside the resort town of Crested Butte, Colorado. The field has been home to the Rocky Mountain Biological Laboratory (RMBL, pronounced "rumble") for 75 years.

Until about 2000, the high-altitude meadow seemed to be resisting the pull of global warming, even though spring seemed to be blooming earlier at lower reaches. Due to heavier-than-usual snowfalls, the meadow was remaining blanketed in white even after the ever warmer spring temperatures arrived.

Since 2000, however, the meadow seems to be catching up with the lower altitudes. It is bursting back to life earlier too now, due to an ongoing drought that has reduced snowfall in the area. It could be the start of a new long-term pattern that sees the meadow more in sync, seasonally speaking, with down-mountain areas. That pattern may be more than just a symptom of global warming. It could even help accelerate climate change, some scientists say.

Regardless of which trends hold true for the future, RMBL researchers agree that their meadow isn't what it used to be.

Out of Synch

David Inouye is a biologist at the University of Maryland in College Park. Based on his observations in the meadow between 1975 and 1999, he published a scientific paper in the Proceedings of the National Academy of Sciences four years ago. His study showed global climate change had forced out of sync low- and high-altitude growing seasons in the study area.

"On average we were getting more and more snow at altitude during that period, and spring was arriving earlier and earlier at lower altitude," Inouye said.

At high altitudes, snow pack governs growing seasons: Nothing sprouts until the snow melts. During the study period before 2000, migratory birds arrived at RMBL hoping to forage on insects and worms. Instead, they found a thick blanket of snow—warming temperatures couldn't keep up with increasing snowfall.

Warmer temperatures also lured marmots out of their winter hibernation. The rodents emerged, only to find their food sources still blanketed with snow.

Winter snowfall in the Rocky Mountains has dropped since 1998. The cause has been a shift in a sea-surface temperature phenomenon known as the North Pacific Oscillation. Similar to El Niño and La Niña, the oscillation affects precipitation patterns in wide areas of the continental U.S.

Inouye believes that climate data he collected from the Rocky Mountain meadow between 1975 and 1999 synced up with the wetter phase of the North Pacific Oscillation. The higher snowfalls fit with scientific models that show global warming will cause increased mountain precipitation due to more moisture-laden storms rolling off the Pacific Ocean.

"I think what we were maybe seeing during the first couple of decades was the effect of global warming, and it now seems to be swamped by the effect of regional climate change," he said.

In a few decades Inouye expects the North Pacific Oscillation to flip back to a wetter stage. This will lead to precipitation in the Rocky Mountains and more out-of-sync seasons, as global warming causes high-altitude snows to accumulate.

Contrasting View

John Harte is an ecologist at the University of California at Berkeley. For the past 16 years he has used electric heat lamps to warm experimental plots of land at RMBL. The artificial temperature increase matches the small rise of a few degrees that global warming climate models project will occur over the next century.

Harte's study results show snows melting earlier and the soil drying. Drier soils store less carbon. Less carbon in the soil means more carbon in the atmosphere, which will accelerate the pace of warming, he said.

Drier soils are also more suited to sagebrush, the hearty shrub that carpets much of the arid West. In Harte's heated study plots, sagebrush is crowding out wildflowers.

The ecologist said the transition from wildflowers to sagebrush only speeds the trend: Sagebrush is darker than most wildflowers and absorbs heat instead of reflecting it.

He noted that a five-year drought has begun to affect natural areas in the Rocky Mountain meadow in similar ways to the changes he has observed in his artificially heated study plots. "I'm quite persuaded by evidence that snow is melting earlier and the Rockies are drying," he said.

Harte believes the drought of the past five years at RMBL is consistent with global warming projections for the Rocky Mountains. The mountains, he added, are 1,000 miles (1,600 kilometers) inland from the Pacific Ocean—probably too far for ocean cycles to exert a strong influence on RMBL's weather.

"The signal we see in the snow pack and snowmelt is like what is projected from climate models just due to global warming, without any ocean oscillation," he said. "It's not proof of anything. But it says the evidence is consistent with this being a global warming signal."

The ecologist said the current drought could persist for the next 50 to 100 years, transforming RMBL's meadow from a summertime wildflower oasis to sagebrush scrubland.

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