By Yereth Rosen

SEWARD, Alaska (Reuters) – Leaves in Alaska are changing color and the rainy season is supposed to begin, but wildfires are raging on in an unusually long and fierce fire season that scientists say is linked to the far north’s long-term climate warmup.

Usually, Alaska wildfires wind down by late July, but this week, the state Department of Natural Resources extended the official fire season to Sept. 30. Last week, Governor Mike Dunleavy declared state emergencies for fires burning north and south of Anchorage.

The most serious blaze is the Swan Lake Fire on the Kenai Peninsula south of Anchorage, which had grown to over 160,000 acres (64,750 hectares) by Thursday and the 3,300-acre (1,335- hectare) McKinley Fire north of Anchorage.

Billowing smoke from the Swan Lake Fire has sent particulate pollution levels in the Kenai Peninsula to some of the worst measured anywhere in the world. Ignited by an early June lightning strike, the fire has snarled traffic and nearly shut down tourism in an area famous for its outdoor recreation.

In the port town of Seward, thick smoke blowing south from the Swan Lake fire blotted out the normally spectacular views of mountains and glaciers and forced cancelation of tourists’ excursions.

“What can you do? Global warming,” said Marlee Hernandez at Exit Glacier Tours in Seward.

“It’s been kind of a botched summer,” said Joe Drevets, who was working behind the counter at Seward’s Sea Bean Café.

The McKinley Fire has destroyed more than 130 structures, 51 of them primary homes, and displaced hundreds of people in the woodsy area, about 80 miles (130 km) north of Anchorage. It was 71-percent contained on Thursday and officials were allowing evacuated residents to return, but 560 firefighters remained on duty.

More than 200 Alaska fires remained active on Thursday, according to state and federal fire officials. In all, 684 fires have burned over 2.5 million acres (1 million hectares) in Alaska this year. Though far short of the record 6.6 million acres (2.7 million hectares) burned in 2004, this year’s fire total is part of a trend.

Big fire years are more frequent as Alaska warms at a rate at least twice the global average. This is the 15th time in the past 80 years that more than 2 million acres (810,000 hectares)burned in a single season, and six of those years have been since 2000, said Tim Mowry, a spokesman for the Alaska Division of Forestry.

Especially remarkable are the ultra-dry and dangerous conditions in Alaska’s most populous region, with some wildfires breaking out this summer even within city limits.

“I’ve been here 40 years, and this is the most extreme fire condition here that I can remember,” said John See, a wildfire expert with the Anchorage Fire Department.

Until this year, there had never been a “severe drought” declaration for Anchorage in the two-decade history of the U.S. Drought Monitor. Anchorage and fire-stricken areas to the north and south of the city passed that threshold earlier this month and moved last week to the more serious “extreme” drought condition.

The fires are part of a summer of extremes in Alaska – record heat, lightning strikes in unlikely places, extraordinary meltdown of glaciers and widespread die-offs of animals, including whales, seals, birds and masses of pre-spawned salmon killed in waters with temperatures measured as high as 80 degrees F (26.7 C).

A late arrival of winter is almost a lock, said Brian Brettschneider, a climatologist with the University of Alaska Fairbank’s International Arctic Research Center.

“Even if our temperatures turned on a dime, there’s so much warmth in the water around Alaska that it is just going to take time for that to dissipate,” Brettschnider said.

After that, the winter ice that forms is likely to be thin, vulnerable to another early spring melt, leaving open waters to draw in more solar heat and feeding the warming cycle, he said.

(Reporting by Yereth Rosen; editing by Bill Tarrant and Sandra Maler)