20 years after the 2003 blackout hit all of New York City, much of the Northeast US and parts of southeast Canada, it remains one of the most significant power outages in United States history. It was caused by an overgrown tree branch in Cleveland, Ohio that hit a power line, triggering a cascading effect that plunged millions into darkness. 

First Deputy Commissioner of Emergency Management, Christina Farrell, was one of the key members of the response team in 2003. She spoke with WNYC's Morning Edition host Michael Hill about how the city responded at the time, and how prepared we are to brace future blackouts.