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World mayors gather at the Vatican to rally momentum on climate change before Paris talks

  • California Gov. Jerry Brown, right, delivers his speech in the Synod Hall as he attends a conference on Modern Slavery and Climate Change at the Vatican, Tuesday, July 21, 2015. Dozens of environmentally friendly mayors from around the world are meeting at the Vatican this week to bask in the star power of eco-Pope Francis and commit to reducing global warming and helping the urban poor deal with its effects. (AP Photo/Gregorio Borgia)

    California Gov. Jerry Brown, right, delivers his speech in the Synod Hall as he attends a conference on Modern Slavery and Climate Change at the Vatican, Tuesday, July 21, 2015. Dozens of environmentally friendly mayors from around the world are meeting at the Vatican this week to bask in the star power of eco-Pope Francis and commit to reducing global warming and helping the urban poor deal with its effects. (AP Photo/Gregorio Borgia)  (The Associated Press)

  • Paris Mayor Anne Hidalgo delivers her speech in the Synod Hall as she attends a conference on Modern Slavery and Climate Change at the Vatican, Tuesday, July 21, 2015. Dozens of environmentally friendly mayors from around the world are meeting at the Vatican this week to bask in the star power of eco-Pope Francis and commit to reducing global warming and helping the urban poor deal with its effects. (AP Photo/Gregorio Borgia)

    Paris Mayor Anne Hidalgo delivers her speech in the Synod Hall as she attends a conference on Modern Slavery and Climate Change at the Vatican, Tuesday, July 21, 2015. Dozens of environmentally friendly mayors from around the world are meeting at the Vatican this week to bask in the star power of eco-Pope Francis and commit to reducing global warming and helping the urban poor deal with its effects. (AP Photo/Gregorio Borgia)  (The Associated Press)

  • A screen displays victim of forced labor Anna Laura Perez Jaimes's wounds as she delivers her speech in the Synod Hall during a conference on Modern Slavery and Climate Change at the Vatican, Tuesday, July 21, 2015. Dozens of environmentally friendly mayors from around the world are meeting at the Vatican this week to bask in the star power of eco-Pope Francis and commit to reducing global warming and helping the urban poor deal with its effects. (AP Photo/Gregorio Borgia)

    A screen displays victim of forced labor Anna Laura Perez Jaimes's wounds as she delivers her speech in the Synod Hall during a conference on Modern Slavery and Climate Change at the Vatican, Tuesday, July 21, 2015. Dozens of environmentally friendly mayors from around the world are meeting at the Vatican this week to bask in the star power of eco-Pope Francis and commit to reducing global warming and helping the urban poor deal with its effects. (AP Photo/Gregorio Borgia)  (The Associated Press)

The latest in the Vatican's meeting of mayors on fighting climate change and human trafficking. All times local.

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11:00 a.m.

Environmentally friendly mayors from around the world are gathering at the Vatican for a two-day conference rallying momentum ahead of Paris climate negotiations later this year.

Pope Francis is expected to address the meeting later Tuesday. He's a new hero to the environmental movement, thanks to his recent encyclical denouncing the world's fossil fuel-based economy that he says exploits the poor and destroys the Earth.

The mayors are expected to sign a declaration at the end of the day demanding that their national leaders approve a "bold climate agreement" at Paris talks in December that keeps global warming at a safe limit for humanity.