The occasion: World Creation Day. The audience: half a million young people from all over Italy, 300,000 of whom had camped overnight on the hillside, sleeping and praying in tents and on blankets as they waited for the Pope to arrive.

When he did, his words were startling. "Before it's too late," the 80-year-old Pope told the rapt crowd, "we need to make courageous choices that will recreate a strong alliance between man and Earth." Exhorting world leaders as well as Catholic youth, he decried global warming and declared, "We need a decisive 'yes' to safeguard creation and a strong commitment to reverse those trends that risk making degradation irreversible."

Then, to close what organizers called the first "eco-friendly" Catholic youth rally, Benedict led his listeners in an outdoor Mass.

Unlike the crowds at garbage-strewn Catholic youth rallies of the past, this audience made good use of the biodegradable utensils and color-coded recycling bags organizers provided. They went away bearing prayerbooks and backpacks made from recycled paper and plastic, and flashlights run on hand-cranked battery chargers — a precursor, perhaps, of the concrete actions that would spring from Pope Benedict's words.

Finally, in a green gesture that is becoming standard practice among the eco-minded, the Vatican arranged to offset the carbon dioxide the event generated by planting trees — many of them in areas of southern Italy damaged by summer fires.

A Sea Change for the Church

Benedict's words would be strong stuff coming from any leader. Coming from the Pope — who, besides ruling a small sovereign state, is the ultimate religious authority for nearly a billion people — they could send a jolt across the globe.

There's more. Consider these recent events:

• A week after the rally, the Pope sent encouragement to religious leaders offering a "prayer for the planet" beside a shrinking Greenland glacier. "Protecting water resources and paying attention to climate change," he wrote, "are important issues for the entire human family."

• In April, the Vatican hosted a two-day Conference on Climate Change where environmental officials, clergymen, and industry skeptics engaged in discussions so heated that some disputes spilled out into the hallways.

• In June, the Vatican announced plans to replace the cracked cement roof of its largest auditorium with a solar roof that will power the hall's lights, heating, and air conditioning, and provide power for other buildings in the Vatican.

• Finally, in July came a watershed announcement: the Vatican would be the first sovereign state on Earth to go carbon-neutral. An eco-restoration company called Planktos had offered, through its subsidiary KlimaFa ("Climate Tree"), to offset the Papal State's carbon emissions by planting a 37-acre forest in Hungary on the Vatican's behalf.

Taken singly, these events aren't earthshaking. Together, they could signal a sea change for one of history's most powerful institutions. Will the Pope follow through with "courageous choices" to fight global warming? Will the Church put its power to work to save the planet?

Is the Vatican really going green?