A new outbreak of spruce bark beetles is killing trees across Southcentral Alaska, as far north as the Alaska Range, fulfilling a prediction by a pioneering Alaska climate change biologist.

A survey completed by state and federal forest officials shows dead spruce trees over nearly 450,000 acres of the region, 30 times more than 2014, and extending 200 miles north of previous outbreaks.

The beetles normally are present in low numbers in Alaska forests, but in the 1990s they exploded across the Kenai Peninsula, turning nearly 5 million acres of big spruce trees red and then ghostly gray. The outbreak was the largest ever at that time.

Heavily hit areas were completely transformed. The disappearance of large, shady trees changed the fire, soil and water conditions on the land and the plant and animal life in the forest, including human life. Downed trunks made terrain nearly impassable.

A new briefing paper by U.S. Forest Service supervisory entomologist John Lundquist describes that destruction in announcing the new outbreak to the north.

"The current spruce beetle outbreak has the potential to expand and intensify and have an immense impact on the values held by people living in Alaska," Lundquist wrote.

But so far, tree damage is patchy. Campers can see a scattering of dead trees near Byers Lake in Denali State Park. The forests of the northern Susitna Valley are generally more varied than on the Kenai Peninsula, where the dominance of spruce made for total devastation.

That outbreak changed lives and made history.

Detailed field research by Ed Berg, then a biologist with the Kenai National Wildlife Refuge, documented the climate change fingerprints of the 1990s outbreak. His evidence became news of the first major biological event driven by climate change worldwide.

Berg found the beetles exploded when a series of at least three summers attained a trigger air temperature. The warming climate had brought those temperatures on the Kenai Peninsula.

The outbreak burned itself out almost 20 years ago. Most of the vulnerable trees had died. The beetles kill only spruce trees larger than 6 to 8 inches in diameter.

Berg retired, but he kept watching as the conditions for another outbreak developed. Trees too small for the beetles to kill in the 1990s rapidly grew larger in newly opened forests. Temperatures, always varying but on an upward trend, hit the three-year warmth he was looking for in 2015.

"The climate trigger has now been pulled," he wrote in an article back then. He added, however, that it might take a few years for masses of beetles to build up to create a large outbreak.

That has now happened. Aerial surveys by the Forest Service and Alaska Division of Forestry counted increasing acres with dying trees on the peninsula and northward, leading to this summer's spike.

"Ed was right. There is another outbreak," Lundquist said. "He had predicted that, because there were a couple of years of hot and dry summers that preceded, the pattern he had identified in that great work of his."

Prediction is a key test of science. Scientists prove their theories when they make specific predictions that are verified by events.

Berg's accurate prediction layers on top of another set of predictions that are also proving accurate. The rising trend of Alaska temperatures is following the projections of computer climate models that said increasing warmth would follow human carbon dioxide emissions.

Charting those rising temperatures on a graph — both the actual temperatures and the projections — the conclusion becomes unavoidable that our region is permanently transitioning to a new ecology with different forests. The beetle is an agent of that change.

Beetle outbreaks have probably occurred here since the ice receded and forests first grew. Berg found evidence of them in the record of tree rings. But earlier outbreaks were patchy and sporadic.

Now temperatures on the peninsula commonly rise into the range for beetle outbreaks, with little respite for trees exceeding 6 inches in diameter.

Warmer temperatures also have moved north, apparently activating the outbreak there, although scientists weren't ready to declare that link definitely. They say evidence of the outbreak is too new.

But Berg said it makes sense. The conditions exist and the cause is the same.

"I was surprised to hear about the northern reach of the beetle kill," Berg said. "I was camping in Denali State Park, and in one of the campsites I saw beetle kill there. That's pretty scary to see it that far north."

He added that the Alaska Range could be a barrier to the continued northward march of the outbreak. But other climate-related stresses on spruce trees have been documented in Alaska's Interior.

Southcentral forests face other pests and other climate stresses, too. The spruce aphid, an invasive bug from Europe, has continued moving north thanks to warm winters, Lundquist said. This summer it reached near Ninilchik.

The changed climate allows new tree species to grow here, too, Berg said. Alaska's climate zones are migrating north. His neighbors in Homer are experimenting with trees from formerly warmer climes.

Property owners north of Anchorage are a couple of decades behind them in dealing with the change. The Division of Forestry has been fielding calls reporting beetle kill and asking what to do, said forest health program manager Jason Moan.

Berg said spraying and removing lower branches can help if a beetle infestation is light, but most spruce trees cannot be saved in a heavy outbreak.

He knows that from experience. In the last outbreak, he lost every tree on his beautiful property above Kachemak Bay near Homer.

No one knows if this outbreak will reach the severity of the 1990s. There are reasons for hope.

The northern forest's patchwork of spruce and hardwoods could limit the beetles and their damage. Also, the region is less populated than the Kenai Peninsula, so the impact on people could be less.

But many large trees remain vulnerable.

"If you've lived through that 1990s outbreak, if you go up there, it will probably feel pretty familiar, as sad as that is," Lundquist said.