"Walker has hinted that what NASA loses in earth science research could be shifted over to NOAA."
Second, NOAA is not operationally or logistically equipped to handle the level of earth science that NASA is performing. NOAA manages a few weather satellites, but has nowhere near the infrastructure that NASA has, and requires, to manage the existing earth science research. Even if you gave NOAA the appropriate money, they don't have the infra or engineers to keep everything flying.
Planetary Radio did a great episode on this topic, but I'm struggling to find it right now.