Former president Barack Obama called climate change an “existential issue” and emphasized the importance of equity in solving sustainability and climate problems Wednesday morning during his talk at an international green building conference in Atlanta.

Thousands of people packed the Georgia World Congress Center to hear Obama at the annual Greenbuild Conference and Expo.

His appearance coincided with the Democratic presidential debate taking place in Atlanta this evening. Climate change has become one of the major issues along the campaign trail for the 2020 election. Ten of the candidates participated in a CNN-sponsored town hall about the climate crisis, and the topic has come up often during debates.

The former president steered clear of political talk, though, and stayed on message during his hourlong question-and-answer session with Mahesh Ramanujam, President and CEO of the U.S. Green Building Council.

Obama, appearing off-the-cuff, discussed a range of issues including leadership, the building of the Paris Accord, how to shape a sustainable agenda around the concerns of all people and helping the next generation become leaders.

Climate change, he said, is one of those things where you can be too late.

“I know of no issue that is more urgent than that,” said Obama and equity must be part of any solution, he said. “It is hard to figure out how we solve sustainability issues and climate change if you also have huge gaps in wealth and opportunity and education because what happens is that as wealth gets more and more concentrated and more and more energy is used up by the few, the many become resentful. It undermines our sense of politics and the sense of community. It is hard for us then to mobilize the body politic around taking collective action.”

Obama’s appearance kicked off the second day of the weeklong conference which features a range of speakers and education sessions for members of the green building community.

Before Obama spoke to the standing room only crowd, Atlanta Mayor Keisha Lance Bottoms shared some of the city’s sustainability successes including its recent recognition as the 100th city in the country to received Silver LEED certification.

The conference concludes on Friday with a keynote from 17-year-old activist Jamie Margolin, founder of the youth climate justice movement, Zero Hour, and Marshall Shepard, an international expert on weather and climate change and a professor at the University of Georgia.