ANCHORAGE, Alaska — Scientists on Monday painted a gloomy picture of the effects of global warming on the Arctic, warning of melting ocean ice, rising oceans, thawed permafrost and forests susceptible to bugs and fire.

"A lot of the stories you read make it sound like there's uncertainty," said Jonathan Overpeck, a professor of geosciences at the University of Arizona. "There's not uncertainty."

The questions scientists continue to address, he said after his presentation at the Alaska Forum on the Environment, are how much of the warming is caused by humans and how drastic long-term effects will be.

Deborah Williams, a conference organizer and former director of the Alaska Conservation Foundation, said Alaska is Ground Zero for observing the effects of global warming because so many natural phenomena are tied to ice and the repercussions of it melting.

"We are the Paul Revere of global warming," she said.

Overpeck reviewed NASA studies showing how Arctic ice has shrunk in size and depth. Climate models 25 years ago predicted a shrinking ice pack.

"What we didn't predict is that it would be so dramatic," Overpeck said.

Scientists predict the summertime Arctic could be ice free before the end of the century, opening up northern sea routes but threatening the existence of polar bears, a marine mammal that depends on sea ice to live.

Other scientists ticked off the effects of warming on fish, forests and tundra.

James Overland, a research scientist with the National Oceanic and Atmospheric Administration for more than 30 years, said the loss of sea ice has meant some marine life has thrived and some has been hurt.

"The marine ecosystem is shifting north dramatically," he said.

Pollock are thriving in warmer water. Pink salmon are being found in great numbers farther north, "an incredible indicator of warming," he said. Crab and other bottom-dwellers who depend on ice overhead for part of the year are suffering.

Glenn Juday, professor of forest ecology at the University of Alaska Fairbanks, said tree growth has decreased at Interior Alaska sites that were promising for commercial harvest. Studies of temperatures at Talkeetna and Fairbanks indicate daily lows are not as low as they used to be. The warming lowers the water available to white spruce, black spruce and birch, Juday said.

"The warmer it is, the less the trees grow," Juday said. Warming also makes them more susceptible to fire and insects.

Vladimir Romanovsky, an associate professor of geophysics at UAF, reviewed effects of warming on permafrost, or ground continuously frozen for two years. Areas of thick permafrost in the far north remain stable but have warmed over 20 years one-half to 2 degrees at a depth of 20 meters, Romanovsky said.

Matthew Sturm of Cold Regions Research and Engineering Laboratory studied shrubs in Arctic tundra by comparing 50-year-old photographs taken along the Chandalar River for the National Petroleum Reserve-Alaska with photos taken recently.

"They all pretty much tell the same story," he said.

Shrubs have thrived in the greater warmth and in turn accelerate warming. Like open water in the ocean, shrubs darken what otherwise would be a mostly white, reflective snow-covered environment, Sturm said.

If warming trends continue, Overpeck said, the globe eventually will get a nasty message from the Arctic: a rise in sea levels. Higher oceans will flow into low-lying parts of the world such as New Orleans, making recovery in that hurricane-ravaged city moot.

"It's hard to imagine why we're wanting to rebuild if we're going to allow global warming," Overpeck said.

Source: Associated Press