President Biden's climate envoy said that King Charles should reconsider his decision not to attend the UN climate conference.
John Kerry said in an interview that it would be "terrifying" if the King could be there.
He was going to go to the conference as a prince.
He didn't attend on the advice of the prime minister.
The next Conservative leader and prime minister will be decided in a leadership election after Liz Truss resigns.
The contest to replace her will be finished by October.
Secretary Kerry said it would be up to the government to decide if they would attend the climate conference.
Charles spent a lot of time campaigning on environmental issues.
He is subject to different rules now that he is king.
Climate action was not considered political by Secretary Kerry.
He said that his leadership has been very important.
In November of last year, as Prince of Wales, the King traveled to Egypt with the government's blessing to urge the Egyptian administration to work harder.
The hosts of the summit warned the UK not to backtrack on the global climate agenda after it was announced that King Charles wouldn't be attending.
Secretary Kerry told the British Broadcasting Corporation on Friday that he had noted some of the decisions that raised questions.
The US is worried about a number of countries that may roll back their climate commitments.