Alex Dews

is policy and program manager at the Mayor's Office of Sustainability

On Thursday, the U.S. Environmental Protection Agency released its sixth annual ranking of metropolitan areas with the most Energy Star certified buildings. For the first time, Philadelphia placed in the top 10, moving up to the number-nine spot.

In 2008, only 28 buildings in the city were recognized through the Energy Star program. Today, there are 210 in the region, which collectively saved $29 million in 2013 alone. And that is only a fraction of the opportunity in the city's building stock.

Philadelphia's big buildings are the key to cutting carbon emissions and putting millions of dollars back into the local economy. Nationally, commercial buildings represent about 20 percent of energy use and greenhouse-gas emissions. In cities, these numbers are much higher. In Philadelphia, more than half of all the energy used in buildings goes to the commercial sector, and 62 percent of carbon emissions come from buildings. When it comes to buildings' energy performance, though, information is scarce.

Imagine buying a car with no fuel economy label. It might seem absurd, but in commercial real estate transactions, it's the norm. That's starting to change now that Philadelphia and eight other U.S. cities have mandated annual energy benchmarking for large commercial buildings. In 2013, more than 1,700 buildings in Philadelphia tracked and reported energy performance using Energy Star Portfolio Manager. Starting this summer, energy ratings for all of these buildings - including schools, churches, office towers, and municipal buildings - will be publicly available.

By using the EPA's free Energy Star tools, owners can see how their buildings stack up to their peers and track the impact of their investments over time. Buildings that score a 75 or higher (out of 100) can earn the Energy Star, just like appliances and lightbulbs.

Mercy Philadelphia Hospital earned the Energy Star in 2013 for its commitment to reducing energy use and costs. In addition to installing qualified lightbulbs, the staff started a simple, effective "Turn It Off" campaign. Each Saturday, one team member checks the lights and air conditioners. If they're still on, the team member turns them off and leaves a reminder for colleagues to "Turn It Off."

Success in energy efficiency is increasingly important. Every summer, heat waves mean higher operating costs in a region that already pays 20 percent more than the national average for energy. Earlier this year, extreme cold set all-time records for energy demand and sent bills through the roof for many commercial customers. Efficient building systems and operations are the best way to insulate against price spikes while maintaining a comfortable indoor environment.

To achieve meaningful reductions in carbon emissions in an increasingly urbanized world, cities have to lead. And buildings, which are our primary source of carbon emissions, are the key.