Does the Pope believe in global warming?

In his strongest declaration yet about climate change, Pope Francis said Thursday he is convinced that global warming is "mostly" man-made.

He also said he has nearly finished writing an encyclical on climate change to be published in June that he hopes will encourage negotiators at a climate change meeting in Paris in December to make "courageous" decisions to protect God's creation.

"I don't know if it (human activity) is the only cause, but mostly, in great part, it is man who has slapped nature in the face," Francis told reporters Thursday aboard the Papal plane en route from Sri Lanka to Manilla, Philippines. "We have in a sense taken over nature."

"I think we have exploited nature too much," he added, mentioning practices like deforestation and monoculture. "Thanks be to God that today there are voices, so many people who are speaking out about it."

The comments marked the Pope's most forthright statement to date on climate change, a topic that has sparked global debate and divided Catholics.

But his remarks should come as no surprise. Since the day of his election as pope, Francis has pledged to make the environment a priority and has spoken out frequently about what he calls a "culture of waste." 

He will have another opportunity to make his case in the Philippines, where he is scheduled to visit Tacloban, the center of the area devastated in 2013 by Typhoon Haiyan, which the Philippines government has said is an example of extreme weather conditions wrought by climate change. Climate change models predict that, as global surface temperatures increase, typhoons will worsen.

Francis will also meet with survivors of Haiyan, which killed about 6,300 people and affected millions more. Some two million people are expected to attend an open-air mass on Saturday in Tacloban, where the Pope is likely to speak about the environment and climate change.

With his Saturday mass, the Pope will likely also indirectly address world leaders working on climate change. Last month in Lima, Peru, almost 200 nations met to broker a global deal to combat climate change. Under a deal reached there, governments agreed to submit plans to rein in greenhouse gas emissions.

But Francis faulted the Lima conference for not doing enough to fight climate change and used his pulpit to urge more action at this year's climate conference in Paris. 

"The Peru meeting was nothing much, it disappointed me. I think there was a lack of courage. They stopped at a certain point. Let's hope the delegates in Paris will be more courageous and move forward with this," he said.