Paris Climate Agreement: What it is, how it started and what happens now that the US has rejoined By Meteorologist Stephanie Weaver FULL INTERVIEW: Paris Climate Agreement Discussion Helen Mountford, the vice president for climate and economics at the World Resources Institute, discusses the Paris Agreement, an accord that President Biden rejoined. LOS ANGELES - President Joe Biden signed an executive order on Wednesday, Jan. 20 — just hours after being sworn in — for the United States to rejoin the Paris Agreement. In November 2019, the U.S. formally left the Paris Agreement and became the first and only nation to do so, distancing itself from international efforts to curb global warming.