There's no need to embed the overlay jpg's directly in the kmz files when those jpgs are freely available from the Berkeley site. Attached is a very small (2KB) .kmz file containing all 12 overlays as links.

WARNING: Do NOT "check" the entire folder after you download the .kmz unless you have lots of virtual memory. Each of the 12 images is about 3500x2000 pixels, and Google Earth will lock up on machines with small amounts of physical memory - at least that's the case on my teensy machine @ work. Just view the overlays one at a time & all will be well.