The Extinction Codex: A Complete Systems Taxonomy of Civilizational Collapse and Extinction-Level Risk Vectors Facing Human Civilization

This monograph presents the first comprehensive, single-framework taxonomy of all credible extinction-level and civilizational-collapse risk vectors facing human civilization. Organized across five categories — Biological, Cosmic/Astrophysical, Geophysical, Anthropogenic, and Exotic/Theoretical — the Codex maps 28 distinct scenarios from engineered pandemic and coronal mass ejection to supervolcano eruption, nuclear atmospheric transformation, methane clathrate runaway, and vacuum decay. The work introduces three analytical innovations absent from prior single-domain threat literature. First, Scenario Zero: the biological substrate collapse already underway through soil mineral depletion, microbiome disruption, hydrosphere contamination, atmospheric degradation, and seed system genetic erosion — framed as the silent accelerant that raises mortality rates and compresses recovery timelines across every acute scenario. Second, a pairwise Interaction Matrix mapping the highest-impact scenario combinations, identifying the terminal cascade sequence most consistent with current observable trajectory. Third, a direct engineering assessment of isolated private survival infrastructure — the bunker class analysis — demonstrating through supply chain, genetic, knowledge, psychological, and ecosystem dependencies why isolated survival fails within 5–15 years across all Tier III and IV scenarios. The Codex is structured in six parts: Part I establishes Scenario Zero as the foundational cascade multiplier. Part II presents the complete 28-scenario threat register with standalone lethality, cascade multiplier score, recovery interference score, impact timeline, and tier classification for each scenario. Part III presents the Interaction Matrix and the five-step terminal cascade sequence identified as the highest-probability compound pathway. Part IV directly addresses the population with resources to act, assessing the five engineering failure modes of isolated survival and the investment strategies that actually produce species-level resilience. Part V establishes the Restoration Paradox — the fundamental asymmetry between demographic recovery speed and environmental remediation timescales — drawing from the companion Presignal preprint (Carter, 2026, Zenodo). Part VI identifies six specific, time-bounded intervention nodes where human agency can alter trajectory, including grid hardening against CME, pathogen biosecurity architecture, soil and seed system restoration, atmospheric carbon drawdown, AI alignment investment, and distributed knowledge preservation. The document carries 37 peer-reviewed citations across environmental science, astrophysics, volcanology, nuclear physics, demography, genetics, and biosecurity. It is released as an independent open-access monograph under the Presignal Research Initiative.