Some mayors have specifically agreed to commitments to expand public transportation and invest in natural climate solutions such as tree canopy and vegetation.
"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.
The "Thanks, Obama" line drew laughs and applause from the audience.
Between July and September, the U.S. GDP, a gauge of economic output, grew at three percent-continuing similar growth reported in the previous quarter.
"Obviously, we're in an unusual time when the United States is now the only nation on Earth that does not belong to the Paris Agreement", Obama continued. "A conveyor belt of some of the strongest hurricanes on record this summer smashed into Houston and Florida and Puerto Rico, and more than two months later, they are still struggling to recover".
Dubbed the "Chicago Climate Charter", Plante and the more than 50 other mayors at the C40 conference are essentially committing to doing what Donald Trump has rejected: following the guidelines outset in the Paris Climate Accord.
Obama told the told the mayors attending the summit that they are America's new front-line leaders on climate change.
The agreement requires the cities to track and publicly report city emissions, advocate for greater local authority and flexibility to take aggressive action on climate, and incorporate the realities of climate change and its impacts into local infrastructure and energy planning.
Obama spoke to mayors in attendance for about 15 minutes acknowledging the difficulty of addressing climate change now that the USA does not belong to the Paris agreement. "We're on that path and we know our American sisters and brothers are".
Emanuel said the current resident of the White House - not mentioning Trump by name - and his environmental officials are in denial on climate change despite facts.
Barrett said he would be discussing Milwaukee's action on climate change.
"You may withdraw", says Emanuel, referring to Trump pulling out of the Paris Agreement. "I applaud Mayor Barrett for taking aggressive steps to bring down carbon emissions levels".
The earliest the USA can withdraw from the Paris agreement is November 2020.