By 2007, the water level at Lake Powell, with greenhouse-gas-emitting Navajo Generating Station in the background, had dropped sharply, leaving a telltale "ring" on rocks. In recent months, the water has risen a bit. New UA research links the drought to global warming.

Related articles:

Preview: Star special report shows how global warming hits homeHuman hands already may be cranking up heatIs our drought a sign of longterm climate change?

Other articles by Doug Kreutz:

Dakota offers satisfying fare, modern flairVault Mine Trail: If you climb it, there's a rewardHike: Madera Canyon's Vault Mine Trail is steep, rewarding Reid Park's rose garden proves its sweet scent Streamside trail is aflutter with birdsButterfly Trail: Beauty and the Butterfly The wonder of wood Biking: Old Spanish Trail round trip ideal for cyclistsBirding: Get early start on Birding TrailTucson Restaurant Review: Pina: Fine food in inviting setting

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Global warming threatens to alter our region's landscapes and lifestyles over the next 50 to 100 years — sometimes subtly and sometimes starkly, scientists warn.

Among their predictions:

● Major forest fires in the West — which have ravaged nearly seven times more land in recent years than in previous decades — will continue to grow in size and number if warming and drying go unchecked.

● Invasive plant species, such as fast-spreading, thick-growing buffelgrass, could profoundly alter treasured desert sites such as Saguaro National Park. A park official says buffelgrass — by driving out native species and fueling huge fires — could "convert desert landscapes into an African grassland."

● Blazing heat, already extreme in Southern Arizona, could rise by 4.5 to 7 degrees or more during this century, based on recent studies.

● Boundaries of the Sonoran Desert could shift as warming temperatures push native plants into new areas.

● The average flowing length annually of Cienega Creek southeast of Tucson — which has declined sharply in recent years — could shrink even more if warming and drought continue. One result: fragile native species of fish and frogs would lose vital habitat.

Other possible impacts of warming in Southern Arizona include failing fruit orchards, changes in mountaintop vegetation and the decline of some bird species.

"This is scary stuff," says Thomas Swetnam, director of the Laboratory of Tree-Ring Research at the University of Arizona. His studies of drought, forest fires and climate change indicate that warming is a very real threat.

"And we know the causes of global warming," Swetnam says. "It is very likely that greenhouse gases introduced at the global scale are the primary cause of recent warming."

Even one of the longtime skeptics of global warming theories in Arizona isn't as skeptical as he used to be.

"You're asking me if it's possible. Of course it's possible," said Robert C. Balling Jr., former director of the Office of Climatology at Arizona State University. "I remind people it wasn't so long ago we were just as convinced we could freeze to death in the future."

In the 1990s, Balling was one of the most prominent climate-change scholars to challenge the idea that human-produced greenhouse gases were heating up the Earth. Today, he has modified his views, and says he thinks the planet will warm over the next century, but he is very skeptical about reports tying global warming to hurricanes, floods and droughts.

Many top scientists say such skepticism is sorely misguided.

"The term we use about the evidence for global warming is 'unequivocal,' " says Jonathan Overpeck, director of the UA Institute for the Study of Planet Earth and a lead author of the 2007 report of the Nobel Prize-winning Intergovernmental Panel on Climate Change.

"We have a high degree of confidence that the Earth is warming," he says. "And the entire West is warming more than the global average."