California has a rich history of environmental activism. When an obscure easterner named John Muir arrived in San Francisco in March 1868, he immediately he asked a local carpenter how to get out of the city. “Where do you want to go?” asked the carpenter. “Anywhere that is wild” replied Muir. Muir proceeded to walk straight through the Central Valley and into the Sierra Nevada, where he would begin his long career as an environmental advocate and an important figure in the establishment and growth of the National Park System.

The environmentalists of Muir’s day worked tirelessly to save beautiful places like Yosemite and, by ensuring public ownership and access, to make them something that all Americans can experience. However, in placing such a strong emphasis on the preservation of especially scenic spaces, the generations that followed Muir neglected the environmental potential of American cities to accommodate growing populations more economically than new low-density developments in, for example, California’s Central Valley. John Muir may have wanted to get out of San Francisco as fast as he could, but in fact one of the easiest ways for California to improve its quality of life and achieve important environmental goals is to get people into San Francisco.

The case for a larger San Francisco is multifold, but it starts with the basic observation that if people want to live there but cannot, they will move somewhere else. By constricting the supply of housing and office space in highly desirable locations like San Francisco, governments force would-be residents to move to less expensive locations where their environmental impact is much greater, and where access to city amenities is limited. According to the National Housing Conference’s Center for Housing Policy, San Francisco was the nation’s most expensive market for homebuyers and renters in 2011. There is a tremendous demand for San Francisco living that is going unmet due largely to local regulation, and reducing these restrictions can be justified economically even in the absence of the positive environmental externalities entailed. Best of all for California’s cash-strapped state and municipal governments, doing so would require no public money, and indeed would provide relief governments relative to the status quo by increasing the ratio of taxpayers to infrastructure.

The environmental benefits of a shift towards California’s cities are undeniable. According to a 2008 study by the Brookings Institution, per-capita carbon dioxideemissions in the San Francisco-Oakland-Fremont Metropolitan Area are only slightly over half the average of America’s top 100 metro areas. Indeed, six of the top 12 metro areas are located in California. This in fact understates the environmental benefits of city living in California, as the unit of analysis is the “Metropolitan Area,” which includes many low-density suburbs that require more energy use per person and thus more emissions. Per-capita emissions in California are generally lower than in other states because California produces a relatively large share of its electricity from renewables, and as Stanford students can attest, the need for air conditioning and heating is mitigated by a generally mild climate. Dense cities like San Francisco emit even less per-capita than the state average because of their high share of trips taken on foot, by bike or on transit relative to automobiles, and due to economies of scale in the heating and cooling of buildings.

Accommodating more residents in places like San Francisco produces many other benefits that are difficult to quantify. By diverting residents away from exurban areas, development in cities protects habitats important for the maintenance of biodiversity and frees space for agriculture in the highly productive fields of the Central Valley. The environmental movement has over the last several years hesitantly embraced cities as a way to make growth more sustainable. Nevertheless, efforts to reduce restrictions on the density of cities within the Bay Area and beyond have been too limited in scale to make an appreciable difference. This is a goal that should be pursued at least as strongly as more expensive policies for curbing pollution like emissions taxes or clean energy subsidies.