Vatican City, Jul 23, 2015 / 12:01 am (CNA/EWTN News).- At a meeting with U.S. mayors at the Vatican this week, Pope Francis hinted at themes he could discuss with the United Nations during his September visit to the states.

Among the most important was the issue of human trafficking, which he said can be a “rebound effect” of environmental degradation. 

“I have high hopes, and believe that the United Nations must take a greater interest in this phenomenon, especially human trafficking caused by environmental issues, and the exploitation of people.”

Francis' remarks followed a July 22 workshop in the Vatican entitled “Modern Slavery and Climate Change: the Commitment of the Cities,” during which dozens of mayors from around the world were invited to present on the theme of climate change and trafficking. 

Many of the mayors present have a history of environmental awareness, including several from the United States.

The daylong workshop was part of a two-day symposium sponsored by the Pontifical Academy of Sciences, titled “Prosperity, People and Planet: Achieving Sustainable Development in Our Cities.”

The meeting comes ahead of several international events focused on the environment, including the U.N. General Assembly's Sept. 25 summit on the adoption of sustainable development goals – which the Pope will address – followed by the climate summit in Paris.

In his address, Pope Francis spoke specifically of the Paris encounter in November, expressing his hope that the meeting “will lead to a basic agreement” on how to reduce the impact of climate change.

The gathering with mayors fell just over a month after the June 18 release of Pope Francis' long-awaited encyclical on the environment, Laudato Si, meaning “Praise be to You.” 

While the 184-page encyclical wades into controversial topics such as climate change, the document also argues it is not possible to effectively care for the environment without first working to defend human life. 

In his remarks to the mayors, Pope Francis spoke of his recent encyclical, explaining that one of his intentions in writing it was to emphasize that “caring for the environment means an attitude of human ecology.”

“In other words, we cannot say: the person and Creation, the environment, are two separate entities. Ecology is total, it is human…you cannot separate humanity from the rest; there is a relationship of mutual impact, and also the rebound effect when the environment is abused.”

For this reason the Pope said his encyclical shouldn’t be classified as a “green” document limited solely to environmental issues, but is rather “a social encyclical, because we cannot separate care for the environment from the social context. Care for the environment is a social attitude.”

One of the most evident signs of lack of care for the environment is the “unfettered growth” of cities, the Pope observed. 

When cities become larger they often grow alongside increasing bands of poverty, he said, explaining that this increases migration, since people to move to the slums and shantytowns of large cities due to a lack of opportunity in the rural world.

Francis then pointed to the growing problem of “the idolatry of technocracy,” which he also touched on in Laudato Si. 

An overemphasis on the use of technology “leads to the loss of work, it creates unemployment, which leads to migration and the need to seek new horizons,” he noted.

“The great number of unemployed is a warning – What prospects can the future offer to today's unemployed youth? Addiction, boredom, not knowing what to do with life – a life without meaning, which is very tough – or indeed suicide.”

Statistics on youth suicide rates are not published in their entirety, he noted, and pointed to another temptation for youth, which is to seek new horizons in projects that present an ideal of life, even if it is a guerilla project. 

Pope Francis then highlighted health risks linked to environmental issues, such as rare diseases that often turn up as a result of different elements used to fertilize fields.

He also indicated other problems linked to the environment, such as oxygen, water and the desertification of large areas of land due to deforestation.

“What happens when all these phenomena of excessive technification, of environmental neglect, as well as natural phenomena, affect migration?” he asked. “It leads to unemployment and human trafficking.”

“Illegal work, without contracts, is increasingly common…and means that people do not earn enough to live. This can give rise to criminal behavior and other problems,” the Pope observed, pointing specifically to the phenomena of human trafficking in the mining sector, which he has recently spoken out against.

“Slavery in mining remains a major issue...Everything has a rebound effect...This can include human trafficking for the purposes of slave labor or prostitution,” he said, and called on the United Nations to step up their efforts in eliminating such phenomena.

Touching on two forms of ignorance identified by philosopher and theologian Romano Guardini, the Pope noted that the first, which is the ignorance God gives us to be transformed into culture, to nurture and dominate the earth, is good.

However, the second, when man does not respect this relationship with the earth, can lead man to abuse creation.

Francis pointed to atomic energy as an example, saying that it “can be helpful, but up to a certain point.” Using the dropping of the atomic bombs on Hiroshima and Nagasaki as an example, Pope Francis said that “disaster and destruction can be caused. It is the second form of ignorance that destroys humanity.”

At the conclusion of his address the Pope explained that the PAS chose to hold a meeting with the world’s mayors because “they are aware of the reality of humanity.”

“The Holy See may make a good speech before the United Nations, but if the work does not come from the periphery to the center, it will have no effect; hence the responsibility of mayors and city governors.”

He thanked them for their work and prayed they would have the grace to be aware of “the problem of the destruction that we ourselves have wrought by failing to care for human ecology, so we might transform ignorance into culture, and not the contrary.”

Following his speech Pope Francis signed a joint-declaration of the mayors, which was then signed by all of the participants.

“We join together from many cultures and walks of life, reflecting humanity’s shared yearning for peace, happiness, prosperity, justice and environmental sustainability,” the joint agreement reads.

It continues: “As mayors we commit ourselves to building, in our cities and urban settlements, the resilience of the poor and those vulnerable situations and reducing their exposure to climate-related extreme events and other economic, social and environmental shocks and disasters, which foster human trafficking.”