"Brazil is back on the world stage," Brazil's president-elect Luiz Inácio Lula da Silva has told cheering crowds at the COP27 climate summit in Egypt.
"The Amazon has huge meaning for the world. We have to prove that a standing tree has more value than a fallen one," he said.
He called for the next COP to be held in the Amazon.
Nations are meeting in Sharm el-Sheikh to discuss tackling climate change.
Just two weeks after his narrow election win, Mr Lula is meeting leaders from the US, China and the EU at the climate conference.
Under President Jair Bolsonaro, who will hand over power to Mr Lula in January, deforestation of the Amazon reached record highs.
Puyr Tembé, an indigenous leader from heavily deforested Pará state, told BBC News that Mr Bolsonaro completely dismantled laws protecting the Amazon and attacked environmental defenders.
By contrast, the incoming president has said he will try to end deforestation and restore the Amazon.
On Tuesday US climate envoy John Kerry said he was confident Mr Lula would bring a complete turnaround on Brzail's approach to the environment.
Former environment minister in Brazil Isabella Teixeira told BBC News that "the world" is now "embracing Brazil at COP27".
While Mr Lula has received a warm welcome at COP27, he faces a divided country at home, with significant opposition in the Brazilian Congress potentially making delivering on his promises difficult.
In order to make progress on his agenda, Ms Teixeira said Mr Lula would need to convince people and Congress members to agree, not disagree with each other.
"Brazil today disagrees. But we are rebuilding our democracy and we must not give up our responsibilities on climate change," she said.
In order to do this, Mr Lula must reverse Mr Bolsonaro's legacy by rebuilding the environmental protection agencies, unfreezing the Amazon Fund which promotes conservation, and tackling criminals in the Amazon, according to Marcio Astrini, executive secretary of Brazil's Climate Observatory network.
He says Brazil is back in the climate game, but that civil society will not hesitate to challenge the new government it if fails to keep its promises.
"When the government is succeeding, we will support them, but if it fails, we will criticise them."
But it will not be easy for Mr Lula to deliver on his ambitious pledges, suggests Roberto Waack, a business leader and chair of Arapyaú Institute.
"The world needs to be prepared for mistakes or failures. It's a complicated problem and we will face disappointments because of the political situation in Brazil," he said.
"You can't just say stop deforestation and the next day the problem is solved," he said.
On Tuesday, young Brazilian activists at COP27 met Mr Lula. "It was hugely emotional, I cried a lot. It is unbelievable to feel part of Brazil again," Gabrielle Alves, an environmental racism researcher who is part of the Clima de Mudança coalition, told BBC News.
Behind the scenes, negotiations between nations are ongoing at COP27 with a final agreement expected on Friday or Saturday.
However there are still wide divisions between countries on key issues.
The question of who will pay the bill for irreversible climate damage remains hotly debated, as developing countries want finance urgently earmarked to cover their losses.
But developed nations are resisting any question of compensation to countries who historically caused the majority of emissions.
There is concern too that the crucial aim to limiting temperature rise to 1.5C - which scientists say is crucial to avoiding the worst effects of climate change - is in jeopardy.