NEW YORK (Thomson Reuters Foundation) - Fight against “fake news” about climate change, the mayor of Paris and a leader in climate policies, said on Monday, taking on a favorite phrase of climate-change doubter U.S. President Donald Trump.

Policy-makers, leaders and the media need to back “the factual truth universally established by scientists” that human activity is driving global warming, Paris Mayor Anne Hidalgo said at a side event to the United Nations’ annual General Assembly, where 193 nations meet to discuss issues from security to climate change.

“Side with the truth,” she said.

Hidalgo heads the C40 Cities initiative, a network of cities making plans to cut planet-warming greenhouse gas emissions along levels agreed upon in Paris two years ago.

Under the climate deal, nearly 200 nations agreed to cut greenhouse gas emissions, mainly from burning fossil fuels, to help protect from droughts, extreme weather and rising seas associated with global warming.

Trump, a Republican, has dismissed man-made climate change as a hoax and has decided to withdraw the United States from the pact.

“Challenge fake news ... which delay(s) awareness” of the risks related to climate change, Hidalgo said.

Trump frequently uses the phrase “fake news” to dismiss news he opposes.

Eight cities in the C40 - Boston, Durban, London, Los Angeles, Melbourne, Mexico City, New York and Paris - are launching a pilot project to try to fulfill the Paris targets on their own.

Cities are responsible for an estimated 75 percent of carbon emissions contributing to climate change and consume 70 percent of global energy, according to the U.N. Environment Program.

Authorities in each of the eight cities will release a blueprint by the end of next year showing how they will meet Paris targets, C40 said.

“Most cities have already done work on climate-reduction planning, but the challenge of the Paris agreement is greater both in terms of the level of reduction and the speed of reduction,” Michael Doust, a C40 spokesman, told the Thomson Reuters Foundation.

Patricia Espinosa, the U.N.’s climate chief, said she welcomed the cities’ commitment.

“I know the power of cities. I come from one of the biggest in the world,” said the Mexico City native.