The Prince of Wales will attend the crunch Cop30 UN climate summit in Brazil next month, the Guardian has learned, but whether the prime minister will go is still to be decided.

Prince William will present the Earthshot prize, a global environmental award and attend the meeting of representatives of more than 190 governments in Belém.

Environmental experts welcomed the prince’s attendance. Solitaire Townsend, the co-founder of the Futerra consultancy, said it would lift what is likely to be a difficult summit, at which the world must agree fresh targets on reducing greenhouse gas emissions.

“Is Prince William attending Cop a stunt? Yes. But that doesn’t mean it’s a bad idea,” she said. “Cop has long been as much about so-called ‘optics’ as it is negotiations. Prince William’s announcement will likely encourage other leaders to commit, and will have the global media sitting up to attention.

“I suspect HRH knows very well that by showing up, he’ll drag millions of eyes to the event. In an era when climate impacts are growing, but media coverage dropping, anything that draws attention should be celebrated.”

King Charles has attended previous Cops, but will not be going to this one.

Gareth Redmond-King of the Energy & Climate Intelligence Unit, an environmental thinktank, said: “All hands on deck – and any prominent, high-profile individual like the Prince of Wales, there helping make the case for the difficult job that needs doing, is almost certainly a good thing.

“[King Charles] was the Prince of Wales when he went to Cop26 [in Glasgow in 2021] and pitched in to help galvanise talks. I don’t think it necessarily needs both of them to go.”

The British prime minister, Keir Starmer, has not yet said whether he will attend the summit, to which all world leaders are invited, with scores already confirmed. He was heavily criticised by leading environmental voices, including the former UN secretary general Ban Ki-moon and the former Irish president Mary Robinson, for appearing to waver on the decision late last month.

Ban said: “World leaders must be in Belém for Cop30. Attendance is not a courtesy, it is a test of leadership. This is the moment to lock in stronger national commitments and the finance to deliver them, especially for adaptation” to the effects of the climate crisis.

“The world is watching, and history will remember who showed up.”