South Fork residents were among an estimated 75,000 people who participated in Sunday’s March to End Fossil Fuels in Manhattan, at the conclusion of the hottest summer since global record-keeping of temperatures began and amid multiple signals around the world that climate change is happening now and getting worse. “I’m here personally because my granddaughter is also here, and I want a livable planet for her and her generation, and, in fact, all living beings,” said Francesca Rheannon of Springs, who is on East Hampton Town’s Energy and Sustainability Advisory Committee.