Despite advances in fuel efficiency and emissions control and the proliferation of hybrid and battery-electric cars over the past three decades, CO2 emissions from transportation sources continue to rise. 

Data compiled by Boston University shows that the majority of that growth has come from large metropolitan areas, and in most urbanized parts of the United States, CO2 emissions have actually increased on a per capita basis since 1990. 

The New York Times put together an interactive map allowing users to see exactly how the average carbon footprint has increased in each of the 100 greatest CO2-producing metropolitan areas in the United States. 

While emissions have almost universally increased (see the San Jose, Calif., metro area for a counter-example), the most significant per capita increases are in cities with stagnating or declining populations.

Cities with exploding populations, like Atlanta, show a net increase in greenhouse gas production but a decrease on a per-person basis.

Neighboring metro areas such as Washington, DC, and Baltimore, demonstrate how much of a role population growth—be it positive or negative—plays in individual CO2 contributions. 

The Times map does a good job of illustrating the what, and the accompanying report describes the why. The dip in the positive trend between 2008 and 2014, for example, reflects the impact of the global financial collapse on Americans' driving habits.

Longer commutes contribute too. Americans are spending more time in rush hour traffic and traveling farther to work than they ever have, to the point where the gains of today's more fuel-efficient cars aren't offsetting the increase in miles driven. 

Some experts fear this trend could continue well into the future, even if electric vehicles become the predominant means of urban transportation, with total trips taken increasing thanks to the availability of ride share options.

The resulting gridlock could actually counteract the more to more-efficient powertrain configurations, especially if fossil fuels remain prevalent in electrical generation.