The Association of Bay Area Governments projects that the nine-county Bay Area region will add nearly 1.5 million residents by 2030. That population growth will not be attributable to a wave of foreign immigration, nor to an influx of newcomers from other regions of the state or the country.

In fact, much of the region's burgeoning population will be homegrown - the children (and grandchildren) of those of us who already live here.

The question is: How and where is the Bay Area going to house its additional 1.5 million residents?

If recent history is a predictor of what we can expect between now and 2030, the region's housing future is not especially promising. From 1999 to 2006, only one county - Contra Costa - produced the overall quantity of housing required to keep pace with its population and employment growth.

And the performance was even worse with respect to affordable housing. Not one county met the needs of its moderate- and lower-income residents, and only six of the Bay Area's 101 cities did so.

In a survey of local elected officials, included in a report by the Bay Area Council, most attribute the failure of their city or county to meet housing production goals to such factors as lack of available land and high construction costs.

But hardly any of those mayors, council members and supervisors identified the real reason their cities and counties have failed to produce sufficient housing to accommodate their growing populations. And hardly any acknowledge the real reason that housing is more expensive and less affordable in the Bay Area than in practically any other region of the country.

It is because the Bay Area, with its excessive land-use regulations, is arguably the nation's least hospitable region in which to build housing.

Indeed, the past 30 years of no-growth, anti-housing activism, led by Bay Area environmental groups, has resulted in counties and cities designating more than 1 million acres of land as permanent open space - perhaps more than any other metropolitan area in the world.

Yet the no-growth, anti-housing environmental alliance continues to agitate for even further land-use restrictions, arguing that the Bay Area is "built out," promulgating what I refer to as "the Joni Mitchell Myth" - that Bay Area home builders have paved paradise and put up a subdivision.

But here's the reality that the no-growth, anti-housing, environmentalist crowd never lets on to the unsuspecting public: Only 16 percent of the region's land area has been developed. And that development includes not only the homes in which the region's 7.2 million residents live, but also schools and hospitals, police and fire stations, libraries and recreation centers, office buildings and factories, shopping centers and supermarkets, churches and synagogues, mosques and temples.

Bay Area environmental groups argue that most of the home building and development that occurs between now and 2030 ought to be confined to the 16 percent of the region's land area that already is developed.

They suggest that most of 1.5 million additional residents expected in the Bay Area over the next quarter century can be accommodated by smaller-scale, infill housing development.

But that requires a suspension of disbelief. Just last year, in fact, UC Berkeley's Institute of Urban and Regional Design issued a report cataloguing every single infill parcel in the state that could be considered a realistic candidate for development.

If housing were built on every single one of these infill parcels, including those here in the Bay Area, they would yield only a quarter of the new housing needed to keep pace with population growth.

So even under the most optimistic scenario, three-quarters of the Bay Area's future housing need is going to have to come from green field development. The region is going to have to zone an additional 2 to 4 percent of its acreage for home building (which would leave the region 80 percent undeveloped).

Bay Area environmentalists refuse to accept this reality. In fact, a consortium of local environmental groups actually proposes that the region add an additional 1 million acres of land to the inventory of permanent space over the next three decades - about the same time the Bay Area will be adding those 1.5 million new residents.

This is the precise prescription for further damping housing production in this region, for further escalating Bay Area home prices, and for making the dream of home ownership that much more unattainable for the next generation of Bay Area residents.

In a paper published by the Harvard Institute of Economic Research, co-authors Edward Glaeser and Joseph Gyourko made the convincing case that "if policy advocates are interested in reducing housing costs," and thereby making housing more affordable, "they would do well to start with zoning reform."

Environmentalists suggest that cities and counties can mitigate their anti-growth, anti-housing policy prescriptions by imposing certain affordable requirements upon home builders. But such requirements have little impact on overall housing affordability, according to economists Glaeser and Gyourko.

Indeed, the best way to make housing more affordable is to do the opposite of what the Bay Area's environmental groups propose, Glaeser and Gyourko conclude. Instead of placing an additional 1 million acres permanently off limits to home building, effectively bidding up the cost of remaining developable land, reducing the implied zoning tax on new construction could well have a huge impact on housing prices.

Bay Area residents ought ask themselves: Why are housing prices three times higher in this region than in much of the rest of the country?

It's not because Bay Area home builders are somehow three times more avaricious than their counterparts in the rest of the country. It's because the region's land use restrictions and other anti-housing regulations are three times more onerous.