VATICAN CITY (KRON) — California Governor Jerry Brown, San Jose Mayor Sam Liccardo and San Francisco Mayor Ed Lee are participating in conversations with world leaders in the Vatican this week about modern day slavery and climate change.

The topics covered at the Commitment of the Cities Conference are a result of Pope Francis’ recently-released letter to all bishops, or encyclical, calling on humanity to protect the environment and human ecology.

Pope Francis’ letter addresses how climate change is affecting the world’s most vulnerable people, many of whom don’t have the luxury of enjoying the advantages of burning fossil fuels.

In his letter, Pope Francis speaks about the importance of respecting Mother Nature and calls for an end to the plundering of her natural resources.

The two-day conference, organized by the Pontifical Academies of Sciences and Social Sciences and the United Nation’s Sustainable Development Solutions Network aims to shed global perspectives on the connection between

devastation of the natural environment and the human environment.

According to a statement released by the Pontifical Academy of Sciences and Social Sciences, global warming is one of the causes of poverty and forced migration and leads to human trafficking, prostitution, organ trafficking, forced labor and other devastations.

Mayors Liccardo and Lee will be among nine U.S. mayors and many more elected officials from around the world who will be participating in the conference.

Lee and Liccardo are expected to speak at the conference about best practices for cities in combating such maladies.

Liccardo is expected to speak on a panel about urban inequality, human development, and social inclusion.

“Building a safe, vibrant, and sustainable community that everyone can call home is chief among my priorities as Mayor and I am honored to have been invited to share how we are tackling the challenges of urban inequality and social inclusion in the most innovative way possible,” Liccardo said in a statement.

Bishop Marcelo Sanchez Sorondo, chancellor of the Pontifical Academy of Social Sciences, said he invites the mayors to participate in a “candid and courageous conversation about ending social and environmental exploitation, two major global crises that remain pervasive and largely unmitigated.”

Sorondo said mayors are the legitimate representatives of their citizens and are well positioned to empower their constituents “to prevent any further objectification of people and the planet.”

Sorondo said cities are where so much human-induced global warming and human trafficking is happening and that the mayors in those cities have a great opportunity to lead against exploitation.

Governor Brown, who will also speak at the event, said this week’s gathering is an opportunity for global leaders to face the common threats of climate change and human exploitation.

“This is about the future of humanity and how we as human beings live and treat one another and the natural world around us,” Brown said.

Brown said this is an opportunity to generate awareness, dialogue and action at the local level on the interconnected harms of climate change and modern slavery.