Chicago officials billed the North American Climate Summit, which began Monday evening, as the first of its kind for the city.
Obama talked about the lack of USA leadership on climate issues in Paris on Saturday.
"But despite that, you're seeing American companies and states and cities continuing to work on this issue", Obama said.
Mayors gathered for the Summit will be invited to make commitments to move forward with significant emissions reductions regardless of action taken by their respective federal governments.
Chicago Chief Sustainability Officer Chris Wheat says the idea is to "fill the void" the Trump administration has left. It also call for them to work with scientific and academic experts to find solutions. The Republican has said the terms of the agreement should be more favorable to businesses and taxpayers.
Terry Crews files lawsuit against male Hollywood agent, claiming sexual assault
The "Brooklyn Nine-Nine" star said he met with WME co-CEO and chairman Ari Emanuel , who apologized for the way Venit acted. He says Sandler seemed shocked by what had transpired. "He's grabbing my nuts".
"Sheltering future generations from the ravages of climate change should be something of an obsession for us", Obama said at the event in Chicago's Streeterville district.
There are many specific pledges in the charter signed today, including: investing in public transit and reducing the carbon footprint in new and existing buildings and infrastructure.
"Climate is changing faster than our efforts to address it", said Obama, who noted that his administration's effort to deal with the issue "wasn't because of some ideological notions about the environment".
Among those attending the Chicago summit are Paris Mayor Anne Hidalgo, San Francisco Mayor Ed Lee, Mexico City Mayor Miguel Ángel Mancera, Montreal Mayor Valérie Plante; Vancouver Mayor Gregor Robertson; Phoenix Mayor Greg Stanton; and dozens of others.
"We live in a time when everything is contested - and so often because of the splintering of our media, it is possible to only occupy a world in which the facts that come in conform to your pre-existing conceptions", he said.