Ten days after US President Donald Trump’s announcement that the US planned to withdraw its signature from the 2015 Paris Climate Accord, it appeared that the rest of the world – including a number of US states – was prepared to continue efforts to fulfil the agreement, without Washington.

On World Environment Day, Jun. 5, world leaders supporting the accord were joined by more than 1,200 US mayors, companies, university presidents and state governors, who in an open letter published online vowed to underpin the deal "in the absence of leadership from Washington."

In the letter, the signatories announced the creation of a US Climate Alliance supporting the treaty, asserting that “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 effort being called bipartisan is led by three state Democratic governors, Jerry Brown of California, Andrew Cuomo of New York and Jay Inslee of Washington. All three governors have been pushing for a low-carbon economy, and all the state governments have provided support for renewable energy.

Calling themselves "climate mayors," the leaders of many major US cities, including Los Angeles, New York, Chicago and Houston – all Democrats – have joined the Alliance. Significantly, the German news agency Deutsche Welle pointed out, the mayor of Pittsburgh, William Peduto, has also joined.  In announcing the US withdrawal, Trump said he “was elected to represent the citizens of Pittsburgh, not Paris."

Alluding to the White House’s decision, Brown said in a press release: “The President has already said climate change is a hoax, which is the exact opposite of virtually all scientific and worldwide opinion. If the President is going to be AWOL in this profoundly important human endeavor, then California and other states will step up.”

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

The philanthropic organization of former New York mayor, billionaire Michael Bloomberg, has pledged to donate $15 million to the UN’s Framework Convention on Climate Change, which among other things helps coordinate compliance with the Paris greenhouse gas reduction targets. The US is obliged to pay into the fund, but so far hasn’t. “We can’t wait for national governments to act on climate change,” Bloomberg commented on Twitter. “For solutions, look to cities.”

Shortly after Trump’s announcement of the withdrawal plans, the EU and China at a bilateral summit declined to consider renegotiating the Paris agreement, as Trump had suggested, but agreed to work together and with other countries as well as willing US states and organizations to reduce carbon emissions.

“Strong transatlantic ties are far more important and far more durable than the latest unfortunate decision of the new administration,” said European Council President Donald Tusk. "No one should be left behind, but the EU and China have decided to move forward," added EU climate commissioner Miguel Arias Cañete.

With the US isolated, some think Canada and Mexico could take up the climate torch on behalf of the Americas. Together with the EU and China, Canada is spearheading a major ministerial gathering scheduled for September to advance the implementation of the Paris agreement and accelerate the transition to clean energy.