CO's rotational ladder lands in every primary CMB band, leaking into temperature maps at 1 to 10 percent of the line signal after cleaning, while Planck dust and gamma-ray analyses reveal a dark molecular component, CO-faint H2, rivaling the bright inventory and lying in the high-latitude regions CMB analyses keep thin masks over. Foreground complexity misjudged at the percent level now bounds the primordial claims the next decade plans to make.
The foreground models inherit the standard interstellar inventory: molecular gas where star formation puts it, traced by CO with calibrated conversion factors, thin at high latitude. Each discovery of dark gas and unexpected cirrus structure forces the masks wider and the templates richer, after the fact.
SCT's interstellar ledger predicts the fog runs thicker than the standard inventory: the pre-existing matter context (P25) seeds the Galaxy with processed, chemically mature material whose molecular phase is older, more widespread, and less tied to current star formation than closed-box chemical evolution builds, and the deposition architecture (P33, P34) strings diffuse envelopes and high-latitude cirrus along inherited structure rather than confining molecules to the thin disk. The growing dark-gas inventory, molecular mass found beyond the CO-bright clouds, in envelopes and cirrus where the masks are thin, is the predicted face of that fuller sky, and the 1-to-10 percent contamination band is the cost of cleaning a foreground richer than the templates assume.
The framework's practical contribution is directional: expect the CO and dark-H2 census to keep growing at high latitude, expect line-ratio and bandpass corrections to keep mattering at CMB-S4 precision, and expect the molecular structure to correlate with the inherited field and cirrus topology (P28) rather than purely with star-forming activity. Foreground convergence comes from measuring the fuller inventory, not from extrapolating the standard one.
This is the same deep-inventory accounting behind the dust budgets and the loop foregrounds. There is no need for the primordial program to be hostage to an undercounted molecular sky.
The inventory is measurable: comprehensive CO and dark-gas surveys establishing that the high-latitude molecular sky matches standard chemical-evolution expectations, with CMB foreground residuals converging under standard templates and no continued growth in the dark-H2 census, would remove the fuller-sky signature. SCT's reading requires the census to keep coming in high; convergence at the standard inventory falsifies it.