Accountant Michael Scott, his wife and their two kids have been living in their first home since 1999, but recently became concerned that it's in a high-risk flood zone in a low-lying area along the east side of the San Francisco Bay.

The area has never flooded due to natural causes, Scott said, but his worry stems from scientific global warming predictions that his San Leandro, CA, home, just 75 feet from Estudillo Creek, could be inundated within 50 years -- if not sooner -- along with dozens of other homes in coastal communities nationwide.

To ease his concerns he's rationalized that by the time global warming creates a worst-case scenario, if it does, his kids will be grown, the house paid off and he'll have plenty of time to flee to higher ground before rising sea levels force him out.

"We decided we like the community here and there's always a chance that the predictions are wrong or that they will send up a red flag and people will take action. It doesn't seem like anything is going to happen for at least 10 years or more," he says.

He hopes.

But what if Scott had to shop for a home today?

"If we were looking for a home, would we move here now? No. Probably not," he concedes.

Global warming is beginning to impact the choices some people make about where to buy a home.

Chances are, only a tiny fraction of home buyers like Scott actually give a toastier planet a second thought when they consider a home purchase.

But low-lying areas and arid, drought-prone regions and others which are likely to first feel the effects of global warming are certainly putting new meaning into the phrase, "Location. Location. Location."

"Everybody is not going to pick up and move today, but with 15 to 20 percent of the population moving every year, there are a growing number of people beginning to ask this question," said John McIlwain, an Urban Land Institute senior resident fellow who holds the institute's J. Ronald Terwilliger Chair for Housing.

"People aren't going to sit there and ask, 'Should I move?', but when they have decided to move they will think about where they should move," said McIlwain.

Impact of Global Warming

Global warming refers to a recent pattern of accelerated increases in Earth temperatures that are disrupting meteorological patterns and planetary conditions that sustain human life.

Nonbelievers abound, but most climate scientists, including those with National Aeronautics Space Administration (NASA); the National Academy of Sciences (NAS); and the World Meteorological Organization all say the planet is nearing a state of emergency and humans are helping push that state to a reality.

Carbon dioxide from burning fossil fuels adds to the heat trapped in the atmosphere, the so-called "greenhouse effect," and that's expanding desert regions, raising temperatures, melting glaciers and ice caps and swelling sea levels at rates more perceptible and measurable than ever.

Scientists say the Earth has the highest levels of carbon dioxide in more than 400,000 years and the 10 hottest years on record since measurements were first recorded 125 years ago all have occurred since 1990.

In addition to burning fossil fuels, another global warming contributing factor is the "heat island" created by replacing natural cooling vegetation with large new home and commercial developments and with paved open space, according to the U.S. Environmental Protection Agency. The urban and suburban heat islands can produce temperatures 2 to 10 degrees hotter than nearby rural areas and aggravate smog, which worsens in hot weather, the EPA says.

Arthur H. Rosenfeld, a member of the California Energy Commission, says temperatures in the Los Angeles area have increased 7 degrees since 1940.

Some major cities, including Chicago, New York and Boston have taken to landscaping the rooftops of buildings to help offset the effect, but they could be too late.

How Hot Is It?

This year, ironically, just before a heat wave swept the nation, killing people in record numbers, the United Nations Environment Programme (UNEP) examining climate change in the desert, produced "Global Deserts Outlook". The report says the deserts of the world are getting hotter and the heat is spreading the desert and its ecosystem beyond existing desert borders.

Call it desert sprawl.

That trend and other climatic changes are beginning to negate predictable temperate weather patterns that generate demand and added property value. As excessive heat and increased smog become intolerable for some home buyers, the reduced demand could be a telling market factor.

"I grew up in Orange County. I've been there for 47 years and we used to have predictable weather patterns -- 85 in the summer and chilly in the winter and it was constant. A few weeks ago it was 115 degrees (F) in Diamond Bar," said celebrity appraiser Randall Bell of Anderson & Sanders LLC of Laguna Beach, CA.

Bell's work is the economic impact of detrimental conditions, such as environmental issues, floods, earthquakes and tornadoes as well as construction defects, soil problems, market cycles and more, including crimes and other stigmas associated with properties. Bell developed the noted "Bell Chart" a matrix of 10 categories, including "Natural Conditions" and their impact on the value of property.

His expertise makes him the Appraisal Institute's designated expert on the impact of global warming on housing values.

"The weather has become a wild card. Good weather is no longer guaranteed. I don't know if its measurable (in terms of an impact on values). There have been no formal studies. My only take on it is there is no place you can move in the U.S. with the assumption of good weather," Bell said.

When it comes to global warming weather, some low-lying coastal regions have already begun to feel the effects, according to scientists who this year said more hurricanes and more intense hurricanes in 2005 were a direct result of global warming.

A home's location right now can mean greater insurance costs, and higher insurance costs already make or break deals. Lenders won't sign off at closing if the homeowner can't obtain adequate coverage. Homes are less attractive as an investment if they come with prohibitively high insurance costs, limited coverage or coverage of last resort.

Is the Coast Toast?

The World According To Al Gore (the documentary and book, "An Inconvenient Truth") doesn't include much of Manhattan, the Florida Peninsula or the San Francisco Bay Area where, within 50 years, homes could be under 20 feet of water because of higher temperature-generated rising sea levels.

"My suspicion is that those who are highly educated are aware of this issue and there is some caution about purchasing in low-lying coastal areas. You are thinking in 50-year increments, which means leaving the property to children and projections in the rise in sea levels in 50 to 100 years," said Philip J. Trounstine, director of the Survey & Policy Research Institute at San Jose (CA) State University.

"The Florida beach coast is not a good long term proposition. Anything right at sea level. There won't be much left of Alviso (CA, just north of San Jose). New Orleans is an example. Take for example, Los Osos (CA). It wouldn't take much of a rise in sea level for some of those properties to be virtually under water. People on genuine beach front property, it seems to me, in the long term, for them it's a dicey proposition about whether you are going to be under water 50 years or 100 years from now unless there's some sort of unexpected reversal," Trounstine said.

With hotter temperatures inland and wetter coastal regions, global warming sounds like a climatic pincher movement that could force residents away from the coast and out of the desert.

Even if the weather doesn't make home buyers rethink the location factor, it is changing what homes they can buy.

McIlwain says home buying considerations affected by worsening conditions along the coast line and elsewhere could be exacerbated by stiffer building codes, zoning restrictions and insurance costs.

The California Energy Commission, for example, recently started requiring new flat roofs to be white and in 2008 will require new sloped roofs to be colors proven to reflect, at a minimum, half as much heat as white roofs.

And then there's the energy card.

Higher temperature fallout from global warming could also force housing choices, but not because of a direct threat to property or the environment, but because of rising energy costs. Higher temperatures require greater energy expenditures and while the choice may not be location-based energy-use will be an issue in the form of a smaller home vs. a larger home.

"There is no way electric bills are going to go down. They are going to do nothing but go up and it will be more severe if you live in the suburbs or 'exurbs' (the ring of rural communities beyond the suburbs). It will also cost you more to cool your house than it does to heat it and that is related to global warming as summers continue to get hotter. The amount you save in the winter is not going to be enough to cover the extra amount you need for the summer," said McIlwain.

That means smaller homes and homes with yet more energy-efficient systems and designs.

Smaller, More Energy Efficient Homes Needed

"You want a smaller house with more insulation. And you'll want to design it in the old fashioned way with over hanging eaves and deciduous tress in the south to block the sun in the summer, but not in the winter," said McIlwain.

The energy card likely will force some home buyers to revisit the location issue because the cost of daily travel today is often factored in the cost of a home.

"I think these large McMansions built on the outer edge of the suburbs are most susceptible to a drop in value as the world changes, traffic congestion gets worse and the cost of driving around will rise," McIlwain said.

"There's a concept of 'house miles.' How many miles do people who live in a home have to travel to get to work, schools, the church, grocery store and anywhere? In its the exurbs or suburbs you have lots of house miles. If you live in town, you have fewer. If you are thinking, 'I can buy a 3,000 square foot home with an acre lot for less and there's a higher price on the smaller home closer to town and I'm going to get the big house because it's cheaper,' well, when you add in the cost of house miles, you increase the cost of the home and you may be making the wrong economic choice," explains McIlwain.

McIlwain says higher energy costs, global warming-related or not, has already prompted builders to bring the cost of a Leadership in Energy and Environmental Design-certified home on par with a conventionally constructed home.

LEED-certified homes come designed and constructed or, in some cases, retrofitted with "green building" techniques and materials. It's an approach that one day will be standard practice because the approach makes the home both more energy efficient and environmentally sustainable.

The LEED approach has the attention of Ceres, a national coalition of investors and environmental groups working with companies to address sustainability challenges such as climate change.

In one area, insurers are poised to offer breaks for home owners who buy LEED-certified homes. Just as hard-to-insure homes could lose value, homes with insurance breaks could also come with increased values that attract the global warming-concerned buyer.

"LEED certifications used to add 10 to 20 percent to the cost of a home. Now developers have learned how to build in LEED standards at no additional capital costs," said McIlwain.

Fundamentals Apply

Experts generally conclude that the threat of planetary meltdown decades in the future isn't going to trigger a mass exodus out of harms way today, but some home buyers do need to consider the impact of global warming.

"Polar ice caps are melting, the water will rise and we know this to be true. But it's a small portion of the population to begin with -- 99.9 percent of the population won't know about it and won't care about it and won't be affected in terms of their property being affected, but in some places the effect could be spectacular," said Trounstine.

"If you are making a decision about a $12 million house at sea level, vs. one on the bluff, it seems to me that the one on the bluff is the best choice," he added.

Others say global warming is a forceful reminder for heightened awareness and special preparations homeowners already need to make based on where they live.

"While global warming may start to be a real estate concern in the years to come, my advice would be to stick with what you can control right now. If you live in or are considering moving to an area that is prone to floods, make sure you have flood insurance; if you live where earthquakes are common, make sure you have taken the necessary precautions to ensure you're home is as secure as it can be," said Holly Slaughter, consumer experience expert with RealEstate.com.

"Each region has it's own quirks, be it wild fires in California or ice storms in New England, so make sure your home is adequately weather-proofed for your region," she added.