When President Donald Trump said he would withdraw the U.S. from the Paris climate change accord because he represents "the citizens of Pittsburgh, not Paris," the mayor of the Steel City immediately rejected the overture.

Trump's line, meant to convey that he was protecting jobs he claims would be lost through the accord, was nevertheless rebuffed by Pittsburgh Mayor Bill Peduto, who tweeted: "Pittsburgh stands with the world & will follow Paris Agreement."

Fact: Hillary Clinton received 80% of the vote in Pittsburgh. Pittsburgh stands with the world & will follow Paris Agreement <a href="https://twitter.com/HillaryClinton">@HillaryClinton</a> <a href="https://t.co/cibJyT7MAK">https://t.co/cibJyT7MAK</a> —@billpeduto

Peduto became just one of many city and state officials signalling that despite Trump's decision to leave the agreement that seeks to cut global C02 emissions, they would forge ahead with their own plans to combat climate change.

'Galvanizing commitment'

"The decision is galvanizing commitment and determination by cities and states and businesses to step up and move forward — and even to a greater degree than was the case before," said David Waskow, director of the World Resources Institute's International Climate Initiative.

Trump said he would withdraw the U.S. from the Paris accord because he represents 'the citizens of Pittsburgh, not Paris.' (Susan Walsh/Associated Press)

"In the United States, emission levels are determined far more by cities, states and businesses than they are by our federal government," former New York mayor Michael Bloomberg, now a UN special envoy for cities and climate change, said Friday in Paris.

"Over the past decade, the United States has led the world on emission reductions and our federal government has had very little to do with it," he said, and pledged the U.S. would meet its commitment to reducing emissions by 26 per cent below 2005 levels by 2025.

Earlier, Bloomberg told the New York Times that a group including 30 mayors, three governors, more than 80 university presidents and more than 100 businesses was negotiating with the UN.

"The fact of the matter is, Americans don't need Washington to meet our Paris commitment, and Americans are not going to let Washington stand in the way of fulfilling it," he said.

'Aggressive action'

Meanwhile, the group known as Climate Mayors has grown to 175 members, all reaffirming their pledge to "honour and uphold the commitments to the goals enshrined in the Paris Agreement."

And Connecticut Gov. Dan Malloy said on Friday he was joining the Democratic governors of New York, California and Washington as part of the United States Climate Alliance — a coalition, they said, "that will convene U.S. states committed to taking aggressive action on climate change."

"In the absence of leadership from the White House in addressing climate change, it is incumbent upon the states to take action in order to protect their residents," Malloy said in a statement.

Connecticut Gov. Dan Malloy said on Friday he was joining the Democratic governors of New York, California and Washington as part of the United States Climate Alliance. (Michael Dwyer/Associated Press)

In fact, many states and cities already have taken action on climate change.

"The federal government is really important — there's no doubt about it — but a lot of aspects of climate policy involve local and state and regional decisions, and that's happening," said Jessica Green, assistant professor of environmental studies at NYU.

In a piece for the Washington Post in February, Green outlined some of those initiatives, including the Carbon Neutral Cities Alliance (of which Toronto and Vancouver are a part), which has pledged to cut emissions by at least 80 per cent by 2050.

WATCH | Salt Lake City mayor pledges to honour Paris accord

Mark Jacobson, professor of civil and environmental engineering at Stanford University, noted that there are 28 U.S. cities that have committed to 100 per cent clean renewable energy.

And in California, considered the leading state in tackling climate change, the state senate just passed a law to go to 50 per cent renewable electricity by 2026 and 100 per cent by 2045.

'Not able to stop'

"There's a lot going on at many different levels that Trump's "not able to stop — and I don't even know he wants to stop," Jacobson said.

For example, nine of the top 10 states that have installed wind power are Republican states, he said.

"Together, a bunch of states can reduce emissions the equivalent to what's needed by Paris," Jacobson said.

Henrik Selin, a professor of international relations at Boston University, agreed that in the wake of Trump's announcement, states and cities will probably be spurred to do even more. But the reverse may also be true, he said.

"States that are sort of skeptical, don't want to take action, they can now hide behind the Trump administration and give them cover not to do it," Selin said.

"I think the leaders will continue to lead and the laggards will continue to lag."

The benefit of federal government involvement, Selin said, is that it would have lifted the laggards and forced them to take further action.

"Now, without the fed push, they can more or less remain where they would have."

White House press secretary Sean Spicer said that mayors and governors are accountable to their own voters.

"We believe in states' rights, so if a locality, a municipality or a state wants to enact a policy that their citizens believe in ... that's what they should do."