Former US President Barack Obama says he is confident that the United States would keep moving "in the right direction" on climate change, although the process might slow down under the current administration.
Before taking office, President Donald Trump pledged to cancel a deal signed by nearly 200 countries in Paris in 2015, which aims to limit rising temperatures by phasing out use of fossil fuels.
Mr Trump, who wants to boost the US coal industry, is expected to announce in the coming days whether he will scrap an accord for which his predecessor campaigned.
Just over three months after leaving office, Mr Obama told a food industry conference in Milan on Tuesday that climate change was a challenge "that will define the contours of this century more dramatically, perhaps, than any other".
He urged big industrialised countries such as the United States and China to lead the way.
"Because of current debate in Washington, it could be that policies move more slowly but I am confident that the United States will continue to move in the right direction," he said.
Policy-making in the last decade has prompted the private sector to invest in both renewable energy and technology to improve fuel efficiency, Mr Obama said.
The United States committed to reducing its greenhouse gas emissions by between 26 per cent and 28 per cent below 2005 levels by 2025 - a level that Mr Trump is unlikely to support.
The European Union has been scrambling to persuade Mr Trump to stick to the deal. Many US companies and several Republican lawmakers, who see it as a way to protect American industrial interests overseas, have also urged him to stay in.
The Paris treaty did not set high enough standards to solve the issue entirely, Mr Obama said but "it put together the architecture and mechanism so that each country can reduce its problem of emissions".