As Donald Trump continues to indicate that he might be willing to change his position on climate change, which he has long called a “hoax,” the president-elect met Monday with former vice president Al Gore, a prominent activist in the fight against global warming.

Gore was in New York for the Climate Reality Project’s 24-hour live broadcast, “24 Hours of Reality,” and was invited to Trump Tower to discuss the topic by Trump’s oldest daughter, Ivanka, who is not registered with a political party and has pushed her father to adopt some positions usually promoted by Democrats.

“I had a lengthy and very productive session with the president-elect. It was a sincere search for areas of common ground,” Gore told reporters after spending about 90 minutes at Trump Tower in Manhattan during the lunch hour Monday. “I had a meeting beforehand with Ivanka Trump. The bulk of the time was with the president-elect, Donald Trump. I found it an extremely interesting conversation, and to be continued, and I’m just going to leave it at that.”

Trump has repeatedly called climate change a “hoax” and said it was perpetrated by the Chinese government to take manufacturing jobs from the United States. But during a meeting with the New York Times late last month, he said he would keep an “open mind” on the issue and acknowledged that human activity might be connected to changes in the climate.

According to an aide to Gore, who spoke on the condition of anonymity to talk about private conversations, the former vice president “made clear in his statements following the election that he intended to do everything he could to work with the president-elect to ensure our nation remains a leader in the effort to address the climate crisis.”

[China tells Trump climate change is not a Chinese hoax] 

While Gore was not personally close to Hillary Clinton — their relationship became strained in the wake of President Bill Clinton’s impeachment and as they each vied for Democratic donors’ support during their respective political bids in 2000 — the former vice president campaigned on her behalf late in this year’s presidential campaign.

Speaking to an audience at Miami Dade College in October, Gore warned that Trump, “based on the ideas that he has presented, would take us toward a climate catastrophe.” Appealing directly to millennials, he alluded to his own narrow loss to George W. Bush in 2000 in Florida and said young people could not afford to vote for anyone other than Clinton.

“The world is on the cusp of either building on the progress and solving the climate crisis, or stepping back, washing our hands of America’s traditional role as the leader of the world and letting the big polluters call the shots,” Gore said. “The choice is that clear. It’s that stark.”

[Why Gore waded into the 2016 campaign] 

But while environmental groups and many scientists have fired shots across the bow at Trump, suggesting that he needs to respect scientific integrity and refrain from appointing advisers who would gut existing environmental and public health safeguards, some prominent activists have been exploring ways to influence the incoming administration. The most obvious target has been Ivanka Trump and her husband because they are seen as the least conservative members of the president-elect’s family.

Ivanka Trump reached out directly to Gore with an invitation to meet with her and others, although he did not know that the president-elect would be included, according to a Gore associate who discussed the private conversations on the condition of anonymity. Gore was “impressed by her thoughtful comments and framing on the issue,” according to the associate, and agreed to stop by for a meeting.

“She clearly is an emissary, and was on this one,” the associate said.

Although Ivanka Trump has said she does not plan to take an active role in her father’s administration, she is one of the most influential people in his life and is a member of his transition team. Her husband, Jared Kushner, is one of Trump’s most trusted aides, and the couple is reportedly house-hunting in Washington.

“That, clearly, is the focal point,” said one national environmental leader, who asked not to be identified so as not to jeopardize any outreach efforts, referring to the couple.

[Scientists and environmentalists brace for a clash with Trump] 

Actor Leonardo DiCaprio recently gave Ivanka a copy of his new National Geographic documentary on climate change, “Before the Flood.” DiCaprio aired the documentary in October on the White House’s South Lawn. Before that viewing, he appeared onstage with President Obama and atmospheric scientist Katharine Hayhoe.