Pope Francis has sharply criticized climate change doubters, saying history will judge those who failed to take the necessary decisions to curb heat-trapping emissions blamed for the warming of the Earth.

Francis was asked about climate change and the spate of hurricanes that have pummeled the U.S., Mexico and the Caribbean recently as his charter plane left Colombia on Sunday and flew over some of the devastated areas.

“Those who deny this must go to the scientists and ask them. They speak very clearly,” he said, referring to experts who blame global warming on man-made activities.

Francis said scientists have also clearly charted what needed to be done to reverse course on global warming and said individuals and politicians had a “moral responsibility” to do their part.

“These aren’t opinions pulled out of thin air. They are very clear,” he said. “Then they (leaders) decide and history will judge those decisions.”

Francis has made caring for the environment a hallmark of his papacy, writing an entire encyclical about how the poor in particular are most harmed when multinationals move into exploit natural resources. During his visit to Colombia, Francis spoke out frequently about the need to preserve the country’s rich biodiversity from overdevelopment and exploitation.

For those who have denied climate change, or delayed actions to counter it, he responded with an Old Testament saying: “Man is stupid.”

“When you don’t want to see, you don’t see,” he said.