Sacramento, Calif. ? The fires sweeping Southern California raise provocative questions about global warming, growth and even evacuation patterns, underscoring how little we know at a time when more people are settling on the fringes of wilderness.

In the last four years, two closely spaced, horrific fire seasons have struck the state, first in 2003 and again in 2007.

In a region known for sporadically devastating blazes, the latest fires could be nothing more than natural variation, or they could be an early sign of the climate extremes that may accompany global warming.

Either way, the impacts of such major fires are wide-ranging and growing. While at least 80,000 fled Southern California fires in 2003, this time hundreds of thousands are on the move.

“We’re really dramatically increasing our population in the western United States in these very arid regions,” said Anthony Westerling, an environmental engineering professor at UC Merced who has studied the role of climate in the 2003 fires.

He warns that along with global warming lurks another, serious risk: sharp climate variations that have sparked major droughts on this continent over the last 2,000 years.

“We’re pushing ourselves closer and closer to the limits of our vulnerability, and we’ve only got 100 years or so of experience to draw on,” Westerling said.

He wasn’t ready to lay the blame for these fires definitively on human-induced climate change, caused by burning fossil fuels that release greenhouse gases.

There are just too many other factors driving droughts, although Westerling and several other scientists say that, as trends are tracked for the next 20 years or so, this dry spell could add a piece to the climate change puzzle.

“Some speculate these extremes will become more normal, if you will,” said Mark Svoboda, a climatologist at the National Drought Mitigation Center at the University of Nebraska.

“I think the jury is still out on that,” he said. “It’s early to say.”