Sir Ed Davey, deputy leader of the Liberal Democrats, met Extinction Rebellion protesters on day 8 of a hunger strike outside the party's HQ in central London on Monday evening (November 25).
During the half-hour meeting, Sir Davey said climate change is "more important than Brexit".
He also called climate change deniers "Flat Earthers", echoing the language of former US President Barack Obama.
The deputy leader also said he wants to see the world ditch coal "by 2025" and the way to do that is "by law", threatening those who use coal with jail.
However, carbon neutral by 2025 is "a challenging date".
The Lib Dems are known for their Stop Brexit message, and Sir Davey took time to slam Brexiteers, saying they are trying to "wiggle out of good European law".
He also said, "pulling out of Europe is a climate crime".
The protesters stated that a demand of the hunger strike is an hour-long meeting with each party leader.
Sir Davey could not confirm the details of a meeting between XR and Jo Swinson, the Lib Dem leader, but said he would "pass it back up the line" to the appropriate people.