Experts in climate change estimate rising sea levels.

Byline: Winston Ross The Register-Guard

NEWPORT - In a room built for 100 people at the Hatfield Marine Science Center library, an Australian-born expert on global warming gives a presentation about rising sea levels with all the sex appeal of a dry classroom lecture.

There are no slides of cities falling into the ocean, of millions migrating across bridges at capacity to escape flooded urban streets, of adorable overheated polar bears.

But that doesn't stop a standing-room-only crowd from spilling out into the hallways, requiring a separate room where overflow attendees of the free lecture can watch on video feed. If the causes of climate change are puzzling to the general public, this much is as clear as the water in a shrinking alpine lake: Rising sea levels can and will affect the Oregon Coast in a big way. The only question is how much, and where.

The International Panel on Climate Change's best estimate for global sea level rise by 2100 is 1 to 2 feet, Laurance "Laurie" Padman told those who gathered at the science center Thursday. "But some analyses say 20 to 25 feet is possible. That's half the range of an ice age cycle in 100 years, which normally takes 100,000 years," he said.

Padman's talk didn't focus much on Oregon, but experts in the state say the coast will face rising sea levels in unique and dramatic ways.

"Sea level rise is a lot more complicated on the Oregon Coast," said Paul Komar, a professor of marine geology and geophysics with the College of Oceanic and Atmospheric Sciences at Oregon State University.

In addition to the global factors that affect sea levels, caused mostly by warming water temperatures, Oregon residents have tectonic forces to contend with - namely, the Cascadia Subduction Zone.

The zone is a fault line where two giant tectonic plates - the Juan de Fuca and North American, or continental plate - are locked tightly against each other.

Every 300 to 500 years, the plates slip, causing a magnitude 9.0 earthquake and a massive tsunami.

In the meantime, the plates shift ever so slowly, up and down, and in different ways along different parts of the coast. From Florence to the southern end of the state, the continental plate slowly is rising, from between 2 to 5 millimeters per year.

As sea levels have been increasing 2 millimeters per year, the land is keeping up with or in some cases rising faster than the water, which means the rising tide has little to no effect.

To the north, however, the continental plate is slipping downward, making the shoreline more susceptible to the rising sea level.

That's where homeowners are seeing significant effects from erosion, threatening several buildings close to the water's edge.

Add to that scenario another factor, and the picture gets worse, said Peter Ruggiero, an assistant professor in OSU'S department of geoscience who studies coastal hazards.

Ruggiero has been studying offshore waves, which have been getting larger over the past several decades with more intensity than the global sea level changes - on average, increasing three to four centimeters (up to 1.6 inches) each year.

"That seems tiny, but think about that over two decades," Ruggiero said. "In 10 years, that's 30 to 40 centimeters. That's a meter (3.28 feet) over a couple of decades. That's a huge difference."

What's more, the "extreme" waves - those that show up in the wintertime, accompanying big storms - have been increasing at a rate of 10 centimeters (3.9 inches) annually, Ruggiero said.

With major El Nino events warming the ocean's waters about every 31/2 years, that raises the mean water level on the order of 40 centimeters (15.7 inches). "That's a century's worth of sea level rise that occurs in the middle of winter for a month or two," Ruggiero said.

What's unclear is exactly how much a rising sea level will contribute to the picture. Scientists are eyeing two critical ice sheets in the northern hemisphere at the moment: Greenland and West Antarctic.

If neither of them melts this century, sea levels are expected to rise 1 to 2 feet by 2100. If both melt, the sea could surge up to 25 feet, Padman said.

Bob Doppelt, director of the Climate Leadership Initiative at the University of Oregon, is part of a group that's been measuring different scenarios and the public's willingness to buy insurance to avoid catastrophic impacts on property.

Based on estimates that a catastrophic change in climate could reduce long-term gross domestic product by 22 percent (akin to Depression era declines) the Oregon researchers applied that figure to Oregon's 2004 GDP, which was $128 billion.

"Insurance principles suggest that if a market existed for `global warming insurance,' the private sector in Oregon would be willing to pay on the order of half a million to $3 billion to avoid the risk of catastrophic outcomes," Doppelt said.

That means an investment along those lines to fight climate change - in cleaner cars, carbon cap-and-trade programs and other clean energy programs - is worthwhile, the group concluded.