Bonn - Todd Stern, the Obama-era official who helped deliver the 2015 Paris Agreement, on Thursday lashed out at the Donald Trump administration's "wrongheaded" decision to abandon the first-ever pact committing all countries to limiting climate change.
Stern, who was Barack Obama's special envoy for climate change, said he was "annoyed, frustrated" by the new president's rejection of a deal that took the world's nations more than two decades to negotiate.
Climate change
"It's completely wrongheaded thing to do," Stern, who left the state department in 2016, said on the sidelines of a UN climate conference in Bonn which he attended as an observer.
"Climate change is a huge challenge, we all know that," he said.
"We are in a... race against time to transform the economy faster than the bad stuff of climate change," he said.
"Trying to say it's a hoax, or it doesn't mean anything, or it's a terrible agreement and the rest of the world is laughing at us, is just so.. ridiculous".
Obama was a champion of the deal which America ratified just two months before Trump, who has described climate change as a "hoax", was elected to the White House.
Trump announced in June that America would abandon the pact, but the rules determine this cannot happen until November 2020.
Drought
The United States is the world's biggest historical greenhouse gas polluter and second only to China for current-day emissions.
This week, Syria became the 196th country to formally adopt the Paris Agreement, leaving America as the only nation in the UN climate convention to reject it.
The pact commits countries to limiting average global warming to under two degrees Celsius over Industrial Revolution levels, and 1.5 C if possible, to avert calamitous climate change-induced storms, drought and sea-level rises.