A Puzzling Collapse of Earth's Upper Atmosphere - NASA Science

Interesting synopsis of a recent Emmert et al paper in Geophys. Res. Lett. My bet is changes in upper atmospheric carbon dioxide levels are probably not the answer (as the authors also state). I'm wondering if we are over estimating the amount of EUV flux, and that the Sun is just being particularly lazy this cycle (hence the low spot numbers, etc). Thoughts?