HANGZHOU, China, September 4 (Reuters) - U.N. Secretary-General Ban Ki-moon said on Sunday that climate change scepticism is over, the day after the United States joined China to ratify the Paris agreement to curb climate-warming emissions. Climate change sceptics dispute the widely held understanding that excessive levels of emissions in the atmosphere cause global warming and harm the environment, and have become increasingly side-lined at international summits. "The debate over climate phenomenon is over scientifically and environmentally," said Ban, adding that the influence of climate change deniers or sceptics has waned.