In one of the world's biggest and most polluted cities, rooftop gardens are springing up in an effort to battle the smog, part of an initiative driven by Mexico City's government.

Roof gardens absorb heat, boost energy efficiency and reduce greenhouse gas emissions and pollution.

The government plans to increase dramatically the number of green roof projects, which covered more than 6,000 square meters last year, with the goal of planting 100,000 square meters by the end of the project — mainly targeting schools and hospitals.

"The patients can come and enjoy this area not only because of the view but because of the green environment this rooftop has," said Dr. Rolf Meiners y Huebner, director of Obdulia Rodriguez Rodriquez Hospital. "You could say physically and emotionally it can contribute to the recuperation of our patients."

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Top photo: Chicago City Hall rooftop by TonyTheTiger, CC license