That number likely came from the 2018 IPCC report which said pretty much this: if something does not happen then by 2030 the there is no realistic pathway to stay belos 2C increase in temperature. World would not end in 2030, but irreversible change would be locked in. Obviously AOC might have been simplifying this or whoever reported on it might have dumbed it down or pushed their own agenda.
The point is, beware making quantified predictions. Climate change is real, but when one makes hyperbolic predictions with a quantified timeframe, and then it doesn't happen, the argument is weakened, and skeptics are reinforced.