Former Vice President Al Gore reminded voters Monday that he knows a thing or two about close elections.

Speaking at a Hillary Clinton rally in Boulder, Colorado, Gore urged voters to head to the polls on Election Day.

“Take it from me, every vote counts,” he said, according to Politico. “Trust me on this. You can consider me an exhibit A of that proposition. Every single vote counts.”

Gore, of course, narrowly lost the presidency to George W. Bush in 2000. Since then, he’s become one of the country’s leading climate activists.

Gore spent much of his remarks discussing the importance of his signature issue, which has largely been ignored throughout the 2016 presidential campaign. Electing Clinton, Gore argued, would be an important step in reversing the damage caused by climate change.

“It’s important to change the lightbulbs, but it’s way more important to change the laws and the policies,” he said.

The former vice president, who served under Bill Clinton, stayed on the sidelines for most of the presidential campaign. He endorsed Clinton in July, but waited until October to campaign alongside her in Florida ― the state that famously cost him the presidency 16 years ago.

“Your vote really, really, really counts. A lot,” Gore told a crowd in Miami.