It’s been on the lips of the president, a concern of the new pontiff, and on the minds of millions: global warming. Lucy Hutyra has heard the call and is seeking answers in her own backyard.

The assistant professor of earth and environment says nearly 70 percent of global carbon dioxide emissions come from cities, which cover only 3 percent of our planet’s surface but are home to more than half of the world’s population. Until recently, few scientists were studying urban areas as unique ecosystems. Hutyra and a team of researchers, however, have spent the past year dissecting the origin of Boston’s carbon emissions, and have begun tracing how urban-generated carbon is stored and processed over time.

“If we are going to have a prayer of actually reducing greenhouse gas emissions, meeting commitments, and creating international treaties,” says Hutyra, “we need to know where carbon dioxide is coming from within cities. It’s the canary in the coal mine, so to speak.”