We can be sure that we are going to have mass movements of people around the world as a result of climate change that is a risk factor for "increased conflicts," said the 44th President of the United States of America during the Climate Change Leadership Summit, on Friday in Porto.

Obama said that one of the factors that triggered the conflict in Syria was the persistent drought that drove farmers towards the cities, radically altering demography and political power.

"I believe in experts and science. I know there are some who do not," said the former US president, stressing that the solution is not to reject science, but to find a common civic commitment.

Asked about the role of traditional media in democracy and the fight against climate change, Obama reported how in the US anyone who watches Fox News has a perception of reality that is different from that of New York Times readers, and that this is one of the reasons for political polarisation in the country.

He added that the solution will involve the traditional media being more creative and recognising the role they play in freedom. "They are the guardians of our democracy and we must find ways to support serious journalism," he said.