All US agencies have an internal appeals procedure if requesters are unsatisfied with the initial response. CEI was unsatisified with responses to their first three FOIA requests.
The appeal was rejected for two of the three requests, and for the third, it was remanded to GSFC for a 'do-over'.
GISS FOI Response to Appeal
Follow-on: Lawsuit (ongoing)
Issues: FOIA Appeals, definition of agency records