US Envoy for Climate John Kerry kicked off his Europe tour with a meeting with UK Prime Minister Boris Johnson in London on Monday before heading to Brussels and Paris.
The purpose of the trip is to "work with European allies to strengthen global climate ambition," the US State Department said.
Kerry met Johnson ahead of the major United Nations COP6 summit that the UK is hosting in November.
Kerry, a former US Secretary of State, was seen appointed to the role by President Joe Biden in November.
He arrived at Downing Street with Alok Sharma, UK's Minister for Employment who is currently serving as President of COP to 10 Downing Street.
Kerry tweeted that Sharma and the Prime Minister were "strong partners in the work ahead".
Departing from Downing Street, Kerry responded to a reporter's question whether it was possible to avert climate catastrophe by saying: "We are working hard."
President Donald Trump administration abandoned the International Paris Climate Agreement, but the US has returned to it under President Biden.
"With the change of administration in the US and the flurry of announcements Biden brought out shortly after he came into office (...), the US position now looks a lot closer to the EU and the UK," said Matthew Paterson, a Professor of International Politics at Manchester University, in an interview with Euronews.
However, the expert warned that it will be "difficult for Biden to get anything through Congress."
"The credibility of the US system to deliver is quite weak," Paterson said, noting that the EU and UK historically had more ambitious climate policies than Washington -- even before Trump.
"In Brussels, Secretary Kerry will meet with representatives of the European Commission," the State Department said.
"In Paris, he will meet with French government officials."