Former vice president Al Gore met with President-elect Donald Trump and his daughter Ivanka on Monday, to discuss climate change.

The president-elect is a well-known climate change doubter—and now, the only climate change-denying global leader—who's taken a stance on climate issues in direct opposition to that of Gore and the world's scientists, who believe global warming is primarily human-caused, and warrants urgent action.

After the meeting, Gore told the press that the meeting was "a sincere search for common ground," and "extremely productive."

According to an aide to the former vice president and 2007 Nobel Prize winner, the meeting was in line with Gore's statements following the election, when he "made clear... 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."

"He happens to be in the New York area this week... and they took him up on the opportunity to discuss the issue," the aide said. 

Gore's meeting came before he embarked on a 24-hour global televised broadcast to spotlight climate science and solutions, known as "24 Hours of Reality."

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Trump's already stocked his transition team and future White House with climate change deniers, even going so far as to put a scholar, Myron Ebell, who thinks the Obama administration's climate regulations are illegal, in charge of the transition team for the U.S. EPA.

Trump has also advocated for the U.S. to back out of the Paris Climate Agreement, a treaty that went into effect last month and involves every country on Earth committing to reducing global warming pollutants such as carbon dioxide.

In 2012, Trump famously called global warming an issue manufactured by the Chinese to make U.S. businesses less competitive. The Chinese recently hit back against that characterization.

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While Gore's meeting may give climate advocates some optimism that perhaps the incoming administration will modify its tone on the issue, reasons for doubt can be found right on the president-elect's schedule. On Tuesday, Trump is slated to meet with ExxonMobil Corp. CEO Rex Tillerson—reportedly a candidate for secretary of state. Also under consideration? Lee Raymond, the former Exxon CEO.

Should Trump nominate Tillerson or Raymond, it'd bring the embattled oil giant, currently facing legal challenges for allegedly misleading investors about climate change risks to its business, to an even more powerful position of influence than it already occupies.

Exxon, more than other major oil companies, has long fought against mainstream scientific findings on global warming, and refused to contemplate a future in which strict limits are placed on greenhouse gas emissions because it views that as unrealistic.