The American Geophysical Union's (AGU) annual meeting in San Francisco this week offered up enough excitement to keep the mega-disaster film industry in business for at least another year. A major theme among the 14,000 scientists in attendance"?was global warming (or "climate change," in polite society).

Al Gore was there to cheer on the experts whose studies document a significant rise in surface temperature in the past century and forecast dire global changes in the next if the warming trend continues. I'll sidestep the controversies and politics on this one (you can judge for yourself via the AGU link at the bottom). But a common thread through the climate sessions"?stitched a clear"?pattern for the world's coastlines: the tide is rising.

Global sea-level rise is a well-documented potential hazard whatever its cause. What does it mean for oceanfront real estate? And a more interesting question: when does it become a material fact in property disclosure?

In more familiar terms, a pro forma for the"?real estate business puts the "upside" for coastal property lines at a bit more than three inches -- and the "downside" at nearly"?three feet"?-- below present sea level by Q1 of 2100. These numbers are from the most recent sea-level forecast by the United Nation's Intergovernmental Panel on Climate Change (IPCC).

That downside means about one foot of sea-level rise over a 30-year mortgage period. A one-foot rise would move the surf zone many feet inland across a seaside parcel. Assuming a 5 percent slope for a sandy beach, this translates to a loss of real estate 20 feet wide times the length of ocean frontage, while the buyer (and lender!) owns the land.

The ocean's eminent domain process is negotiable, but at great cost. Rising sea level introduces all sorts of potential real estate consequences, in terms of future property access, development, maintenance, risk exposure, lot footage (or lack thereof), and other costs of ownership.

This is on top of existing hazards in the coastal zone, such as hurricane-force winds, storm surges, and local, state and federal coastal construction controls and environmental protections.

And the rapid change in sea level ignores other factors the experts have found, such as the loss of protective barrier islands beneath the rising tide, and subsiding land beneath Gulf Coast population centers, which in places sinks three times faster than the sea is rising.

But wait. It may be worse. A new study published just this month says the IPCC's last forecast got it wrong by limiting its climate analysis to a computer model. The new study takes into account actual observations, such as how sea water expands when warmed, and how much water is added to the oceans by glaciers and the Greenland Ice Sheet, which contributes one quarter of the global sea-level rise and is now melting up to three times faster than just six years ago.

These factors, says the new study's author, Dr. Stefan Rahmstorf, double the projected sea-level rise over the next century. And that doubles our 30-year forecast to two feet of gradual inundation and many more feet of shoreline encroachment.

Under this new scenario, "what is now a once-in-a-century extreme flood in New York City (with major damage, including flooded subway stations) would statistically occur about every 3 years," if sea level were just 3 feet higher, says Rahmstorf.

Okay. It's not a silver-screen mega-disaster. Yet, anyhow.

Most states require that buyers be told whether the sale property is in a FEMA-mapped Special Flood Hazard Area. Increasingly, coastal states also compel the seller, if not also the seller's real estate agent, to inform prospective buyers about regulatory coastal zones and environmental protections that may affect the use and value of the property. These are facts material to the transaction, in other words.

Is it any less reasonable for a buyer to expect to be warned about the insidious taking of his or her land by the rising tide, and the hidden"?costs of ownership resulting from it?

I'd like to know what you think!

By the way, the IPCC's next forecast of global sea-level rise is scheduled for publication in February 2007. Whether it incorporates Rahmstorf's "double threat" remains to be seen. (The odds aren't bad, though...he's also the lead author of the IPCC's draft forecast!)

Stay tuned.

Check out what the experts said at AGU. Search for "global warming", "sea level rise", and "climate change" at the AGU website!