The SPA Fellows Committee (SPAFC) reviews the Fellows nomination packages of SPA members and makes ranked recommendations to the Union level committee which selects the yearly class of AGU fellows across all the sections. The SPAFC is comprised of 12-15 SPA members identified and selected by the SPA President and the current chair of the SPAFC. Significant effort is made to create a diverse committee which aids in maintaining a diverse group of nominees going forward to the Union level.
A short description from the SPAFC on their process: We strive to have a diverse committee, which really helps with maintaining a diverse group of nominees going forward to the union level. We acknowledge our biases and read all of the packages. We complete an initial top, middle and bottom ranking, before discussing each package. We then rank each package and send the top 7 or so (depends on the year) with a few supplemental candidates to the Union committee. We write this up into a final report for the Union committee as well as write up suggestions on how to strengthen the rest of the packages. Once our report reaches the Union committee it sounds like they have a similar process, picking often around 4 candidates from each AGU section.
A more detailed description of the process and the committee formation can be found
here.