1) Table of contents
 2) Overview
 3) Multidisciplinary Data Centers 
 4) Climate and weather
 5) Satellite data
 6) Hydrology and glaciology
 7) Environmental chemistry
 8) Geophysical and mapping data
 9) Instruments and field experiments
10) Oceanography
11) Miscellaneous data
12) Software and documentation

Each (major) section has a "Subject:" line, so you can search on the
subject title above to find the section quickly.