It’s rare for a current or former leader of one of the world’s largest energy producers to testify under oath about climate change. That’s why a New York courtroom was packed on Wednesday to see ex-Exxon Mobil Corp. Chief Executive Officer Rex Tillerson take the witness stand and explain that the company knew for years how it was a significant threat to the world.

“We knew, we knew it was a real issue,” Tillerson said. “We knew it was a serious issue and we knew it was one that’s going to be with us now, forevermore, and it’s not something that was just suddenly going to disappear off of our concern list because it is going to be with us for certainly well beyond my lifetime.”

Tillerson, who resigned in 2016 to become President Donald Trump’s first Secretary of State, was testifying in a trial over a securities fraud lawsuit by the New York attorney general. The state alleges Exxon intentionally misled investors about the way the company accounted for the financial risk of climate change. Tillerson rejected the claim, but also took the opportunity to weigh in on the existential threat of global warming.

During 3 1/2 hours of testimony, he cast Exxon in a favorable light, in contrast to claims by environmentalists and some government officials that the company helped trigger climate change and exacerbated the crisis by hiding it from the public.

Tillerson didn’t deny Exxon’s role in creating the problem — which wasn’t what the trial was about — but in his nuanced view, the company had done its best to address the issue once it became apparent. He also said there may be plenty of blame to share, given that Exxon was providing products demanded by society.

Humanity has a hard time making changes to address the impacts of climate change because of the world’s never-ending demand for economic development and improved standards of living, which is tied directly to fossil fuels, he said.