Despite 60 years of stern reminders from Smokey Bear, wildfires are scorching more and more of America lately. About 2.9 million acres burned each year across the U.S. between 1985 and 1995, but since then, the average has jumped to 6.5 million acres annually, including a massive 9.2 million acres that burned nationwide in 2012.

It's enough to give the impression — contrary to what Smokey says — that we may have lost our knack for preventing forest fires. Either that, or the fires are just getting worse.

"We are seeing a significant trend," says Rick Ochoa, fire weather program manager at the National Interagency Fire Center in Boise, Idaho. "Over the last 10, 12 years, fire activity has been much higher than normal."

The problem isn't that we're losing our touch, though. In fact, it's partly that we're a little too good at fighting wildfires — by oversuppressing them for decades, people disrupted natural fire cycles and let too much wildfire fuel build up. Forestry managers now light controlled burns to clear out this excess debris.

More people also now live near forests than in the past, raising both the stakes and chances of a fire. From 2001 to 2012, humans started six times more wildfires than lightning did. Backyard burn piles and arson are two of the top human causes, although cigarettes, campfires and catalytic converters are also often to blame. California's 87,000-acre La Brea fire in 2009 was reportedly started by a cookout at an illegal marijuana farm.

But Ochoa worries, as do many scientists, that there's another, even more dangerous culprit fanning the flames: global warming. "We still have a long way to go on prescribed burns," he says. "But I would say that while we are making improvements on that, in some regards the global warming is outrunning our ability to do it."

Wildfire seasons tend to oscillate between severe and calm every couple years, but scientists have begun noticing an overall upward trend in the acreage burned, if not necessarily the number of fires (see graph above). It seems to correspond with the ongoing increase of U.S. temperatures that's widely blamed on greenhouse gas emissions.

"It was probably sometime in the '90s, maybe late '80s, when I really noticed it personally," Ocha says. "But if you look back at the research, the last 10 to 15 years, they're much higher than what we've seen in the last 30 years in terms of fire activity. And the dominant factor has been the climate change."

How does climate affect wildfire?

U.S. Forest Service firefighters battled a fire in the Angeles National Forest north of Glendora, California, in 2012. As usual, most wildfires in recent years have occurred out West. Idaho saw the largest area burn in 2012 with 1.7 million acres, followed by Oregon (1.3 million), Montana (1.2 million) and California (870,000). The 2012 fire season burned the third-highest acreage in U.S. history, trailing only 2006 and 2007, an outcome that's not surprising in the context of climate. 2012 was also the warmest year for the contiguous U.S. in 117 years of record-keeping, and nearly two-thirds of the country was experiencing moderate-to-exceptional drought by late summer.

Despite much higher rainfall, though, the East Coast is far from fireproof. South Carolina had its worst wildfire in 30 years in April 2009, forcing thousands to evacuate at the height of Myrtle Beach's spring tourist season. Georgia's Okefenokee Swamp burned for four months in 2007, sending thick smoke 250 miles north to Atlanta. And New Jersey's Pine Barrens — an eccentric ecosystem with orchids, carnivorous plants and rare pygmy pines — contains some of the densest wildfire fuels in the country, equivalent to more than 1,300 gallons of gasoline per acre in some places.

Longer and larger droughts are forecast as the climate heats up, which will in turn feed bigger wildfires all across the country. Even now, delayed snowfall and early snowmelt in the Sierra Nevada is straining one of the West's main watersheds, and overall U.S. precipitation is down 10 percent since 1966. Many also blame the spread of pine beetles — which are rapidly turning swaths of forest into firewood — on rising temperatures.

"The primary driver is climate change, the fact that we're seeing warmer years and more droughts," Ochoa says. "That means fuels are drier, a greater amount of insect damage and earlier snowmelt."

Reducing greenhouse gas emissions is widely seen as the best hope for combating climate change, and that's already proved to be an uphill battle. But there are still lots of things anyone can do to prevent forest fires — when they need preventing, that is.

What causes wildfires?

Lightning strikes a tree
Fire is a natural occurrence in every U.S. state except Hawaii. Sparked by lightning, natural wildland fires clean out dead or overgrown plant matter, exposing the soil for new plant growth and preventing dangerously big future fires.

They can also have customized effects for specific ecosystems. In Alaska, for example, springtime fires help warm up the frigid soil, and pitch pines living along the East Coast — especially in the fiery Pine Barrens and Florida Everglades — rely on wildfires to help them reproduce.

As Europeans streamed into North America during the past few centuries, they were often surprised by the large wildfires they encountered, and a well-meaning assumption soon became tradition — forests on fire were seen as forests in trouble, and most wildfires were extinguished while they were still small. This had drastic ecological consequences as the fire fuel built up over decades, setting off waves of wildfire when it finally did burn out of control, often during a drought.

Today, forestry officials start controlled, low-intensity burns for a variety of ecological tasks, mainly clearing out dry, dense debris that could fuel a fire. More than 2 million acres are now torched nationwide by prescribed burns in an average year, up from less than 900,000 acres 15 years ago. And it's still not enough.

Most wildfires caused by humans begin when flames escape from burning debris piles, a problem that can be alleviated by obeying local burn bans or simply checking the weather. While the No. 2 cause — arson — isn't as easy to prevent, there are still thousands of wildfires started across the country each year by mere carelessness.

Flicked cigarettes and abandoned campfires are two well-known fire starters, but cars, trains and various other mechanical equipment can also provide a light. The catalytic converters on automobiles — which serve an environmental purpose by filtering pollutants from tailpipe emissions — can heat up dry vegetation beneath an idling car, igniting a wildfire. Trains, tractors and other industrial workhorses sometimes start fires by shooting sparks into dry grass or brush, although spark arrestors greatly reduce that risk.

"People have to be extra careful with things like campfires, catalytic converters," Ochoa says. "We can't control the lightning, but we can control our actions."

Images: David McNew/Getty Images; Andriano/Shutterstock

Editor's note: This story has been updated since its original publication on Aug. 18, 2009.

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.