Bring up the subject of climate change, and the first point of discussion will usually involve warming climate and sea level rise. However, an overlooked chapter of climate change involves ocean acidification, which will be the subject of a screening of the NOVA special, “Acid Ocean,” the next installment of the Sea Change environmental film series at WHAT’s Julie Harris Stage this Saturday at 7 p.m. The documentary details how oceans are absorbing more atmospheric carbon and