More than 1,200 US mayors, companies, university presidents and state governors pledged by Monday to uphold the Paris Agreement to combat climate change. It is a bid to circumvent the move by President Donald Trump to withdraw from the landmark accord.

In an open letter posted online, the signatories vowed to continue their support of the deal "in the absence of leadership from Washington."

"The Trump administration's announcement undermines a key pillar in the fight against climate change and damages the world's ability to avoid the most dangerous and costly effects of climate change," the letter says.

US Climate Alliance

On June 1, President Trump said the US would withdraw from the 2015 Paris accords, a historic deal in which 191 states and the European Union agreed to a series of measures to mitigate the effects of human activity on climate change. A key facet of the agreement was each country's ability to determine its own contributions based on its economic and social needs.

The same day, the governors of the US states of California, Washington and New York announced the United States Climate Alliance in opposition to Trump's announcement. Several other states quickly followed suit, most notably Massachusetts and Vermont, which have Republican governors. Many other states are expected to support the alliance in the coming days.

According to the Financial Times, the states that have so far agreed to the deal would together represent the world's third largest economy, just behind China and the US and ahead of Japan.

The states have been joined by the leaders of tech giants like Amazon, Google, Apple, Facebook, and Microsoft, as well as representatives from industries such as Nestle, Nike, Unilever and Starbucks.

'Paris is good for economic development'

In addition, the leaders of many major US cities, who have dubbed themselves "climate mayors," have joined the alliance. Los Angeles, New York, Chicago and Houston have signed up and, significantly, Pittsburgh Mayor William Peduto is also a signatory.

When announcing his plan to withdraw from the Paris Agreement, Trump said "I was elected to represent the citizens of Pittsburgh, not Paris." The remark drew umbrage from Peduto, not the least because Pittsburgh voters chose Hillary Clinton by an overwhelming 80 percent margin in 2016.

Trump has often used the specter of former coal and steel boom towns like Pittsburgh to push his message that the accord was bad for the US economy, but Peduto was having none of it.

"Pittsburgh is the example of why the Paris Agreement is good for economic development: such work is good for business too," said Peduto, citing how the renewable energy industry has added a significant amount of jobs to his city's once flagging labor market.

"We've rebuilt our economy on the future and our people, not the past," he added. 

'Americans don't need Washington'

Former New York Mayor Michael Bloomberg, who now acts as the special envoy for cities and climate change at the United Nations, has been tasked with coordinating the efforts from all the parties to stick to the deal.

"Americans don't need Washington to meet our Paris commitments, and Americans are not going to let Washington stand in the way of fulfilling it," Bloomberg said after a meeting with French President Emmanuel Macron and Paris Mayor Anne Hidalgo.

Despite Trump's determination to withdraw, the earliest possible date for Washington to walk out is November 4, 2020 – one day after the next US federal election.