US President Donald Trump (R) walks with the President of the European Council Donald Tusk in Brussels, Belgium, May 25, 2017. [Photo/Agencies]

Once in a while there comes a time when just a single action changes for better or for worse the course of the world. The 21st century, during its short span, has experienced quite a few such moves, with one being made by the leader of the richest and strongest country of the world on Thursday.

The consequences of the move can only be guessed as of now. Yet it doesn't take rocket science to fathom that US President Donald Trump's decision to pull the United States out of the 2015 Paris climate change agreement makes the future of concerted global action against climate change uncertain.

The signs of the times to come were visible at the end of March, when Trump signed the "Energy Independence Executive Order" to "annul" the Barack Obama administration's legislation on reducing coal, oil and gas production and curbing carbon emissions.

By ordering a review of Obama's Clean Power Plan and slashing the funding for the Environmental Protection Agency, Trump made it almost impossible for the US to honor its international climate commitments, the Paris climate agreement included. Ever since there were murmurs that Trump would pull the US out of the Paris pact.

Announcing his decision, Trump, who has dismissed climate change as a hoax, said: "The United States will withdraw from the Paris climate accord" and would seek to begin new negotiations to re-enter either the Paris accord or an entirely new transaction "on terms that are fair to the United States, its businesses, its workers, its people, its taxpayers ..."

That the US under Obama's leadership and China led by President Xi Jinping played a decisive role in negotiating the Paris agreement is common knowledge. The two countries' announcement of drastically curbing their respective emissions ensured widespread participation in the Paris pact. Which means Trump's move to withdraw the US from the pact could also have severe diplomatic consequences, as other countries, its close allies included, might no longer expect Washington to honor its commitments.

Making China's stance clear even before Trump's announcement, Premier Li Keqiang emphasized on Thursday that Beijing will stick to the commitment to fulfill its Paris pledges during his visit to Berlin.

"I was elected to represent Pittsburgh, not Paris," Trump asserted in his announcement. To which Pittsburgh Mayor Bill Peduto replied: "Pittsburgh stands with the world and will follow the Paris agreement."

While in Paris, French President Emmanuel Marcon stated bluntly: "I tell you firmly tonight: We will not renegotiate a less ambitious accord. There is no way. Don't be mistaken on climate; there is no plan B because there is no planet B."

Since Trump has pulled the US out of the Paris pact and thus global climate leadership, joining "a small handful of nations that reject the future" as Obama said, the rest of the world, including China, which is committed to realizing Xi's vision of jointly building and protecting our shared home, have come together to express their united resolve to do even more to protect the one planet we've got.