Abstract: Observed changes in atmospheric CO₂ concentration during the instrumental period and isotopic signatures back to the Little Ice Age are likely explained by natural biogeo-chemical feedbacks, with no detectable anthropogenic contribution. This is supported by mass-balance reservoir routing showing short CO₂ residence times of 3.5–4 years, stable Keeling plot intercepts of −13.2‰ over centuries demonstrating overwhelming biosphere dominance and undetectable fossil-fuel influence, unidirectional precedence of local temperatures → CO₂ across all timescales from the present to ~500 million years ago, and thermodynamic considerations that question the physical meaningfulness of a global mean surface temperature (GMST). IPCC Bern model parameters show instability across assessments, violate mass conservation, and introduce unsupported source discrimina-tion. The global bomb-¹⁴C pulse from nuclear testing exhibits single-exponential decay (e-folding time 17.2 years) matching observations over 55+ years, which directly falsifies the Bern model's multi-exponential structure, permanent airborne fraction, and mul-ti-millennial CO₂ persistence claims. Critical examination of conflicting airborne fraction definitions reveals foundational inconsistencies in IPCC CO₂ attribution. These convergent lines establish that natural processes can explain observed CO₂ variations with negligible human influence. A unified first-principles synthesis shows that a modest natural top-of-atmosphere radiative imbalance of ~2.6 W m⁻² can account for the observed rise in atmospheric CO₂ via temperature-driven oceanic outgassing and enhanced soil respira-tion, without detectable anthropogenic contribution.