As the world's one billion Catholics wait for white smoke to rise above the Vatican, signaling the election of a new pontiff, the quality of air elsewhere will go a long way toward shaping the legacy of retiring Pope Benedict XVI. Among the many titles Benedict has been given over his eight-year reign, the "Green Pope" is certainly one of the most unexpected. But to Vatican observers, Green Pope is entirely appropriate, as the pontiff has made environmental awareness a key tenant of his tenure.

Benedict wasn't the first environmentally conscious pope. In 1990, Pope John Paul II went on record during a speech on the World Day of Peace urging Catholics to regard the natural world as one of God's creations worth protecting. By the time Benedict first put on his papal robes in 2005, caring for the environment had become an important part of the church's doctrine. Benedict gave the issue an even higher profile. He delivered homilies and speeches asking world leaders to take seriously the harm being inflicted on the planet. "If we want justice and peace, we must protect the habitat that sustains us," Benedict said on the 2010 World Day of Peace. Not long after, the influential Pontifical Academy of Sciences, a scientific arm of the Vatican, released a report on climate change recommending that world leaders cut carbon dioxide emissions, reduce existing pollution, and prepare for the inevitable impacts of a changing climate.

Benedict also made moves on his home turf. He approved a plan to cover the Vatican's Paul VI hall with solar panels, enough to power the lighting, heating, and cooling of a portion of the entire country (which covers, of course, a mere one-fifth of a square mile). He authorized the Vatican's bank to purchase carbon credits by funding a Hungarian forest that would make the Catholic city-state the only country fully carbon neutral. And several years later, he unveiled a new hybrid Popemobile that would be partially electric.

At a time when the church was dealing with more pressing structural issues within its ranks, some of Benedict's moves could be seen as simply good PR—inexpensive changes to build good will. Yet certain Vatican watchers see Benedict's efforts as genuine. "I think it's remarkable how much attention he gave to the environment; this for him was a big theme," said Walter Grazer, an adviser to the National Religious Partnership for the Environment and former spokesman for the U.S. Conference of Catholic Bishops (USCCB). In this regard, Benedict's advocacy, says Grazer, is likely to set the tone for a successor tasked with making the church's pastoral teachings more aligned with issues of modern life.

As world leaders gathered in half a dozen cities during Benedict's papacy to discuss global emissions treaties, Benedict did not participate, lacking an element of diplomatic gravitas as a head of state of a physically small country. Where Benedict did exert influence, however, was injecting morality into the environmental debate. Changing light bulbs or saving a wild animal by protecting habitat wasn't about saving money, Benedict implied, but was a religious obligation. "It's clear the church is now on the side of protecting the environment, seeing it as God's creation and something that should be respected," said Tom Reese, a Jesuit priest and senior fellow at Georgetown University's Woodstock Theological Center. "I think that the leaders of the environmental movement are now realizing the church is an ally."

The impetus for the church's environmental advocacy isn't all spiritual. There is obvious concern for how climate change will affect material quality of life, especially for the disadvantaged. Last year, the USCC, the Vatican's U.S. arm, issued a statement saying that the human response to environmental challenges "will affect poor and vulnerable people at home and around the world."

Benedict has echoed the same sentiment, at times stating publicly that the countries emitting the most greenhouse gas emissions aren't the ones feeling the most damaging impacts of rising oceans, extreme storms, and scarcity of water. "He has a great concern for what was going to happen to the poorest people as a result of environmental destruction," said Grazer.