US climate envoy John Kerry has warned that the European Union and United States must revive their joint efforts to fight climate change before the damage becomes irreversible.
In Brussels for his first face-to-face talks with EU officials since the change of government in Washington, Mr Kerry warned: "We face an extraordinary crisis."
As secretary of state under former president Barack Obama, John Kerry worked with EU capitals to build the 2015 Paris Agreement on climate, only to see the next US leader Donald Trump pull Washington out of the pact.
Now, under President Trump's successor President Joe Biden, John Kerry has returned to government as climate envoy.
It comes as Britain is due to host a new United Nations climate gathering in Glasgow in November to renew the world's efforts.
"So, as I come here to renew conversations with our friends in Europe over our cooperation on climate - ;which was extraordinary in the lead up to Paris - it will have to even be stronger," Mr Kerry warned.
He was welcomed by EU vice-president Frans Timmermans, who is leading Brussels' Green Deal growth plan, and who said of the Americans: "They are back. They are back in Paris."
The US envoy was to sit down with European Commission president Ursula von der Leyen and her top team.
"This is the moment," Mr Kerry warned. "Glasgow is the last best opportunity that we have. The best hope that the world will come together and build on Paris."
But he said getting the Paris agreement alone was not enough, warning that even if countries meet their commitments global temperature could rise dangerously.
"And we're not doing all that we set out to do in Paris. So, this is the moment for countries, common sense governments people to come together and get the job done. We can do it."
Mr Timmermans welcomed him and promised: "We are going to be working hand in hand to make a success of Glasgow.
"I'm absolutely convinced that the United States and Europe working together, we can move mountains."