LA JOLLA, Calif. -- Sea-level rise threatens cities around the world, and academic leaders must talk about it differently to help people grasp the potential dangers and costs, climate experts said last week.

Researchers must detail effects at the local and regional levels, members of the Association of Pacific Rim Universities (APRU) Sustainability and Climate Change Program said as they met at the University of California, San Diego. They need to talk shorter time windows, mentioning impacts in 2050 as well as in 2100. And they should drive home to people that actions to limit climate change can help protect their children and grandchildren from huge economic and social impacts.

"Sea-level rise is not a problem that's going away," said Dan Cayan, a climate researcher at the Scripps Institution of Oceanography at UC San Diego. "In some sense, this is an important investment. This is a multigenerational issue."

Climate researchers from around the world gathered for three days at UC San Diego to share information and formulate strategies. They discussed the importance of talking about sea-level rise and climate change as they brainstormed what advice they should give to university presidents. During that session, some of the APRU members urged more of an activist role, saying too much time already has been lost.

"People who don't believe climate change is real, and sea-level rise is real, are really few and far between," said Bernard Minster, a UC San Diego professor and Scripps researcher.

The conference took place just after sea-level rise and climate change happened to surface on the national stage. At the Republican National Convention, presidential nominee Mitt Romney in his acceptance speech derided President Obama's position on the issues.

"President Obama promised to begin to slow the rise of the oceans," Romney said as some in the audience snickered, "and to heal the planet. My promise is to help you and your family."

Obama in his speech at the Democratic National Convention said that "climate change is not a hoax."

"More droughts and floods and wildfires are not a joke. They are a threat to our children's future. And in this election, you can do something about it."

The scientists who met here asserted that spreading some basic facts about sea-level rise may be helpful. Higher temperatures are causing oceans to swell and glaciers to melt, they said, spawning sea-level rise. Increases now and over the next few decades are the result of greenhouse gas emissions over the past 50 years, making some change inevitable.

By the end of this century, they said, seas will climb 80 centimeters, or roughly 2.6 feet. That number could grow to as much as 2 meters, or 6.6 feet, particularly if the ice sheets in Greenland and Antarctica melt entirely, said Helen Fricker, an associate professor at the Scripps Institution of Oceanography.

By 2300 sea levels could lift 10 feet to 13 feet, she added.

The rising seas will affect the lives of millions of people and cost billions of dollars, the researchers said. Half the world's population lives within 62 miles of a coast.

Some areas more threatened than others

Sea-level rise has the potential to affect some places more than others, even within the same state, the experts said.

For example, in California, the impact will be felt more in the south than it will in the state's north or in Oregon and Washington, Cayan said. Two trends contribute to that phenomenon, he said.

The ocean plate is descending below North America at the Cascadia subduction zone, which runs from northern Vancouver Island, British Columbia, to Northern California. The land there is rising as seismic strain builds, Cayan said, making sea level rise less.

It's likely not permanent, however. An earthquake with a magnitude of 8 or higher would stop the land from rising and also likely would bring about additional sea-level growth of 1 to 2 meters (3.3 to 6.6 feet) in the area, he said.

"This could be a great game changer as far as sea-level rise," Cayan said. It would be "instantaneous sea-level rise of the sort Japan saw a year ago" after its magnitude-9 temblor.

The other factor making sea-level rise higher in Southern California could be winds, Cayan said. There was a study that surmised east-to-west winds are driving storm surges that are pushing waters. If those winds calmed, he said, that likely would stop the comparably higher sea effect in the region.

In California, sea-level rise threatens the coastline's homes and other buildings, including San Francisco International Airport, APRU members said. It also endangers freshwater supplies, which in turn could have a big impact on agriculture. The state exports many of its crops across the country.

The bulk of California's water passes through the Bay Delta region roughly between San Francisco and Sacramento. Rising seas could cause saltwater intrusion. Additionally, as the state's snowpack melts earlier because of warming, Cayan said, there is more runoff from higher elevation, which increases flooding.

Key cities threatened

Large population centers in the United States already imperiled by sea-level rise include New York, Boston, Miami and Tampa, Fla., said Trevor Davies with the Tyndall Centre at the University of Southampton in England. Elsewhere in the world, rising waters are likely to affect London, Bangkok, Hong Kong, Tokyo and Shanghai.

"Asia has the largest overall exposure," Davies said.

Predicted urban population growth will compound the hazards, he said. London expects to grow to 9 million people within a decade. The U.K. government has a strategy to reduce greenhouse gas emissions 80 percent by 2050, Davies said.

Desalination plants could help provide water in large population centers, but they also increase carbon pollution, Davies said.

Sea-level rise also could be a major problem in Australia, where 80 percent of people live in coastal cities, said Steffen Lehmann, director of the Centre for Sustainable Design and Behaviour at the University of South Australia. He is urging widespread use of demonstration projects to develop superior green building districts that would cut energy use.

"We are running out of time," Lehmann said. "We need real action on the ground. We need to have real breakthroughs."

Jakarta, Indonesia, faces significant water inundation, said Jatna Supriatna with the University of Indonesia, Jakarta. Gov. Fauzi Bowo wants to build a large sea wall at a cost of $20 billion.

Some at the conference argued that walls aren't the best solution to manage rising seas, however. They damage sea environments and are prohibitively expensive for most places in the world, said Charles Kennel, director emeritus of the Scripps Institution.

The Netherlands has a 100-year strategy and plans to spend $2.5 billion per year for the next century, he said, but that country has a short coastline. Venice, Italy, decided to invest €5 billion ($6.4 billion) on tidal gates to hold back water, because the city sees its buildings as priceless, Kennel said.

"The expense of doing that is an instructive number," he said of the gates.

The gates are supposed to be built to withstand 80 centimeters of sea-level rise, but it is not clear how long that will protect the city, some at the conference said.

Some argue it would make more sense just to retreat from certain areas, Kennel said.

"I cannot imagine that the right solution out is to keep the ocean out via sea wall," Kennel said. "The better solution is to learn how to live with the dynamic ocean."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500