Last of a three-part series
Each December a hardy flock of birdwatchers scatters across Mecklenburg County for the National Audubon Society's Christmas Bird Count, which has tracked bird movements for more than a century.
Here's what the numbers say about Charlotte's birds: They're moving north as temperatures warm. Eighteen of the 20 most common backyard species spotted last Dec. 27 have shifted their winter ranges northward over the past 40 years, national data show. The average distance was 116 miles.
Polls show Americans are increasingly dubious about global warming, even as most climate scientists say they're ever more sure that it's real. Oblivious to science and politics, Carolina wrens and cedar waxwings seem to signal climate change with their wings.
The evidence is firmest in North Carolina on the coast, where a state science panel expects a 1-meter increase in sea level by 2100 and beach towns are scrambling to save eroding strands.
Charlotte's birds are among the hints of statewide shifts as temperatures inch higher. The tendency is northward and upward: stonefly nymphs moving higher up mountain streams; coastal frogs croaking in Piedmont backyards; tropical fish cruising the temperate coast.
Even scientists convinced of climate change are wary of claiming proof that it's at work. More often, they say such indicators fit the patterns one might expect from a changing climate. And they note that more powerful forces, such as habitat loss, also are reshaping the state.
"It's not just climate change we're facing," said Paul Super, a science coordinator at Great Smoky Mountains National Park, where armadillos and South American fire ants have appeared.
"It's the pressure of an increased population and increased use of the park, of exotic species being introduced, of atmospheric deposition with metals. All of that is stressing the park in one way or another, and climate change is just another stressor."
North Carolina's average winter temperature has risen about 1 degree since 1981. Multiyear droughts have scorched the Carolinas twice in the past decade. A water war between the states reached the Supreme Court. The Arbor Day Foundation put Charlotte in a new plant-hardiness zone in 2006, and area golf courses are replacing bentgrass greens with more heat-tolerant Bermuda.
Climate models say more volatility lies ahead: warming temperatures, stronger hurricanes, more floods and droughts.
But models can't reveal problems we haven't yet imagined, said ecologist Steve McNulty, a U.S. Forest Service climate researcher based in Raleigh.
Deep in the Carolinas' drought of 2000 to 2002, previously healthy red spruce trees began dying on Mount Mitchell. The trees were being killed by Southern pine beetles, which bore their way into trees. Normally they're kept at bay by the cool temperatures of high elevations.
Scientists found that airborne nitrogen blown from coal-fired power plants in Ohio had increased the trees' number of needles, while shrinking their roots. The fertilized trees grew well - until drought struck.
During the dry spell, the needles quickly sucked up available water in the soil but their skimpy roots couldn't find more. Without water, the spruce couldn't make the sap that repels the beetles. The insects invaded and quickly killed the trees.
Researchers never would have suspected the one-two punch of acid rain and climate change could have triggered such fast, fatal results, McNulty said.
"Interactions that we have not envisioned will likely cause an increasing number of unexpected and unwelcomed surprises in the future," he said. "What makes them so disturbing is that if we're not looking for them, we're going to be least prepared to deal with them when they occur."