As Ben Carson moves toward his confirmation hearings for secretary of the Department of Housing and Urban Development (HUD), the question remains how exactly his influence will be felt. Once Carson assumes this role, any choices he makes can have spillover effects that contribute not only to housing stock, health risks, and living conditions for our most vulnerable populations, but also to the very quality of our air. Depending on his decisions, climate change, and air quality conditions could worsen by unlikely sources  —  namely, affordable housing and transit-oriented development.

Gentrification is defined by the Oxford dictionary as "the process of renovating and improving a house or district so that it conforms to middle-class taste." Such a benign definition can betray families and whole communities being subjected to this process sans proper planning and forethought. Yet gentrification, as defined by the Centers for Disease Control and Prevention (CDC), paints a more realistic picture; simply put, it results in the serial displacement of communities.

While the exact causes of gentrification can be heavily debated, the unexpected, mostly hidden effects surrounding it should be cause for concern. There are many known effects of gentrification on communities, with higher rates of birth defects, asthma, cardiovascular disease, and cancer all among the CDC's major causes for concern. One commonly overlooked issue: the precipitous decrease in air quality between gentrified and lower-income neighborhoods, which, in turn, further compounds a diminished quality of life for those who've been pushed out.

When families are displaced, it creates a spatial mismatch between jobs and resources that were previously a walk, bike, or bus ride away. Spatial mismatch can result in longer periods between employment and higher rates of unemployment. This burden, while not as impactful for the upper and middle classes, can be immediately detrimental to a family struggling to make ends meet.

Dan Rinzler, senior policy analyst with the California Housing Partnership Corporation, speaks to this fact:

When low-income people are displaced from transit-accessible areas to the urban periphery due to skyrocketing housing prices, as has been the trend in the Bay Area and other coastal markets, they are forced to drive long distances to get to work. In combination with the fact that low-income people are more likely to own older and higher-emissions vehicles, this increase in [vehicle miles traveled] VMTs likely has a negative effect on air quality and [greenhouse gases] GHGs.

As Rinzler notes, this sort of changed behavior of displaced communities rears its head in ways that are even longer lasting than a sudden peak in unemployment.

As Transit Oriented Developments increase in popularity to support the environmental and financial benefits, they too often unintentionally lead to further gentrification of communities. Since 2007, the Environmental Protection Agency, Department of Transportation, and HUD have been working together to promote and enable affordable housing near transit sites. Research from the University of California–Berkeley tells us that, when transit is improved or made more available to a neighborhood, the property values of the neighborhood indeed go up.

While those statistics sound great on face, Berkeley's 2013 Urban Displacement study found that 48 percent of census tracts and more than 53 percent of low-income households were in neighborhoods at risk of or already experiencing displacement and gentrification pressures — a problem compounded by the ostensible solutions offered with expanded public transit.

Traditional TODs are typically hailed as a good thing, but without affordable housing strategically placed, their benefits are quickly diminished.

"Transit-rich neighborhoods are attractive places to live for many people, and this demand often translates into higher rents and property values," Rinzler says. He has also observed the transit-oriented displacement of low-income residents. "For this reason, investment in affordable housing near transit is critical for preventing displacement of low-income households in the context of Transit Oriented Development."

Perhaps more important than housing and transportation inequality is the overlooked benefits for the environment, if urban planners were to commit to keeping affordable housing close to TODs.

"We now have strong evidence that affordable housing near transit generates greater absolute reductions in vehicle miles traveled and greenhouse gases [emitted] than housing for higher-income groups on the same land," Rinzler adds. "All income groups are more likely to drive less and take transit more if they live in location-efficient areas such as TODs, but the important point is that the greatest greenhouse gas reductions come from housing that is affordable to low-income families and individuals."

Miriam Zuk, a professor at UC–Berkeley and senior researcher for the Urban Displacement Project, speaks to the need for continued efforts to support affordable transit-oriented development, even if the immediate impact metes out higher start-up costs:

There is enough evidence that … we need transit investments, but it does result in higher costs of housing. Some forethought, planning, and prevention needs to happen to ensure that existing residents are able to stay when housing prices increase and that these transit investments are able to serve a wide diversity of users  —  people with a diversity of incomes, needs, and destinations.

As more states and cities start to experience growth comparable to California, it is important they consider this research in city planning. On the other side of the country, in Charlotte, North Carolina, a new light rail extension is currently underway. One of the largest advantages of this new TOD will be connecting university-area students and families to resources throughout the city by way of public transportation. City leaders would be wise to strategically place affordable housing within a close proximity to transit to not only prevent gentrification, but to mitigate potential pollution and air-quality effects for the whole city.

Despite these facts, the Charlotte City Council has been slow to push forward on affordable housing, especially in new developments centered around transit. The issues are getting so increasingly worrisome that within the last months one city council member had actually called for a temporary moratorium on new apartments until a solution can be found  —  though ultimately the moratorium was not legally obtainable by city council at the time.

Some private sector companies are now aligning their entire missions to alleviating these issues.

"Our commitment to innovation is allowing for advanced approaches to improving quality of life in North Carolina. The GS&P Charlotte team is working with a number of clients to reduce congestion and improve local air quality across the state while continuing to innovate through creative partnerships to support the growth of smart cities across the Carolinas and beyond," says Sean Flaherty, a transportation planner with Gresham Smith and Partners.

Driving through Charlotte, it's all too easy to spot shells of families' homes — places where people once slept and cooked and lived — now boarded up and dilapidated, perhaps literally on fire. Many of these houses will soon be replaced with beaming buildings that hold apartments and condos in a price range that is inconceivable for what even the average family would call a deal, thus offering little chance for those of a lower income to remain in their current neighborhoods. The choices these people must now make in order to work, live, and survive will affect both their own quality of life and the shared air quality of the entire city.

Research that Flaherty's team has done helps detail the exact effects that gentrification can have on pollution, past the general claim that being further from transportation centers leads to higher greenhouse gases.

"Many municipalities experience high levels of pollution due to auto-exhaust. The City of Charlotte's home county of Mecklenburg experiences nearly 90 percent of ozone pollution as a result of auto emissions and as population continues to boom, air quality impacts will continue to grow," Flaherty explains. He continues:

As seen in Charlotte and many other communities, transportation issues are not limited only to crumbling roads and disgruntled drivers but an unhealthy community due to congestion and associated pollution. Ground level ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen and volatile organic compounds in the presence of sunlight. Breathing ozone can trigger a variety of healthy problems including bronchitis, emphysema and asthma.

The effects of affordable housing created adjacent to TODs reach far beyond air quality. Increased economic productivity for counties and local municipalities, community health, and increased economic and academic opportunities for lower-income residents are all among the quantifiable benefits of affordable housing.

"Connecting workers to jobs generates economic activity around transit stations. Higher density around these stations can also increase tax revenue to local jurisdictions, as well as bolster transportation systems by increasing transit ridership," Rinzler says. "People have even been shown to lose weight by living near transit  —  likely generating reductions in medical costs  —  and low-income people can spend more on essentials when they live in affordable housing. Long-term, helping low-income children avoid displacement and grow up in economically diverse neighborhoods around transit stations could boost their earnings as adults."

While "gentrification and climate change" and "displacement and poor air quality" aren't the type of terms one would immediately put together, ignoring the correlation could be not only be extremely dangerous, but costly to our economy, environment, and to the future prospects of our most diverse communities.

Pacific Standard is the award-winning magazine for readers interested in working toward forward-looking changes to private behavior and public policy. For more stories that matter, sign up for its email newsletter or subscribe now.