PARIS, FRANCE - NOVEMBER 30: United Nation Secretary General Ban Ki-Moon welcomes US President Barack Obama as he arrives for the COP21 United Nations Climate Change Conference on November 30, 2015 in Le Bourget, France. More than 150 world leaders are meeting for the 21st Session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (COP21/CMP11), from November 30 to December 11, 2015 on November 30, 2015 in Paris, France. (Photo by Thierry Orban/Getty Images)
