Pope Francis has urged a large gathering of world leaders at the United Nations in New York to respect humanity's "right to the environment".
He also called on financial agencies not to subject countries to "oppressive lending systems" that worsen poverty.
In an allusion to the Church's teachings on sexual minorities, he called for respect for the "natural difference between man and woman".
He went on to visit the 11 September memorial for a multi-faith service.
After a silent prayer, the pontiff met relatives of some of the victims of the attack in 2001.
Pope Francis later visited a Catholic school in the heavily Hispanic New York neighbourhood of East Harlem.
The crowd in the gym of Our Lady Queen of Angels School included more than 100 immigrants, who greeted Francis with songs.
One eyewitness wrote on Twitter: "He's (Pope) having a blast in Harlem. Big smile. #PopeinNYC".
In a wide-ranging speech at the UN, the Pope said the universe was "the fruit of a loving decision by the Creator" and that humanity "is not authorised to abuse it, much less to destroy it."
He said he hoped a forthcoming summit on climate change in Paris would produce a "fundamental and effective agreement".
He addressed topics including girls' education and drug trafficking. He welcomed the deal between Iran and world powers on its nuclear deal, calling it "proof of the potential of political goodwill".
He also condemned "ideological colonisation by the imposition of anomalous models and lifestyles which are alien to people's identity" in what was understood as a reference to Western support for gay and transgender rights in other countries.
At a memorial service at the September 11 Memorial Museum, he prayed for those killed in the attacks and for healing for their relatives.
Catholics in America:
80 million baptised as Catholics
Six of the nine Supreme Court justices are Catholic
31% of the US Congress (22% general population)
One Catholic president (JFK) and one vice-president (Joe Biden) in the history of the US
Six Catholic Republicans running for 2016 presidential nomination, the most ever
Source: New York Times
About 80,000 people are expected to watch the procession as he makes his way to Mass at Madison Square Garden on Friday night.
Nearly 20,000 are set to attend the service at the major sporting and concert arena.
Thousands lined Fifth Avenue on Thursday evening as the Argentine pontiff made his way to St Patrick's Cathedral for evening prayers.
The Pope arrived in New York from Washington, where he delivered the first-ever papal address to the US Congress.
In the speech, he urged a humane response to migrants, an end to the death penalty and better treatment of the poor and disadvantaged.
Next he will go to Philadelphia, Pennsylvania, where he will speak in front of Independence Hall and celebrate Mass at a Catholic families' rally.