PARIS (Reuters) - French President Emmanuel Macron on Monday promised to hold a referendum on revising the constitution to include references to the environment and fighting climate change. Macron has been under fire from left-wing factions of his centrist party for failing to do enough to combat global warming despite pledges to spend billions of euros to speed up moves to a greener economy. He told the Citizens’ Climate Council that he was willing to include mention of biodiversity, the environment and tackling climate change in Article 1 of the Constitution. “It will be put to a referendum”, he added. Parliament’s upper and lower houses must also agree to the referendum. France’s Green Party has gained momentum over the past two years, drubbing Macron’s ruling party in regional elections early this summer. Macron loyalists worry the Greens could erode his base of support on the political left in the 2022 presidential vote. Last month, France’s highest administrative court gave the government three months to show it is enacting climate policies that will ensure it meets its commitments on reducing greenhouse gas emissions. Macron established the Citizens’ Climate Council in response to anti-government “yellow vest” protests that sprang up in late 2018. Some within the council have denounced it as a talking shop.