The timeline to 3000
The century resolves in three acts — layering, the danger window, and a stratified settle — but the trajectory does not end in 2100. Committed warming and sea-level rise extend the regime for centuries.
Layering
Crisis curves rise but rarely sync. Cognitive/pollution exposure already near-universal; functional heat episodic. The cheapest decades to install stock.
Danger window
Heat, water, grid, demographic and institutional curves synchronize. Trajectories bottleneck or fork here — the decisions that lock in buffer vs envelope.
Stratified settle
Outcomes resolve into a survivability regime: buffered zones with managed heat, and a chronic-risk envelope of months-long functional exposure. Not uniform collapse, not restoration.
Committed plateau
Even with deep cuts, committed warming and sea-level rise persist for centuries. Populations have redistributed toward buffered latitudes and elevations.
Slow reversion
On strong paths, temperatures slowly draw down over centuries-to-millennia; ice and sea level lag far behind. The Holocene envelope is not restored on any human-planning horizon.
Committed warming
Even under deep, immediate emissions cuts, the climate system carries momentum. Ocean thermal inertia, ice-sheet response and the long atmospheric lifetime of CO₂ mean that temperatures plateau rather than fall within the century, and sea level continues rising for centuries regardless of the path. This is the floor beneath the survivability regime: the buffer can be widened, but the baseline cannot be undone on a human timescale.
The slow reversion
On strong-mitigation paths, the very long run does bend back. Over centuries to millennia — roughly the 2300–3000 horizon — natural carbon sinks and slow drawdown pull temperatures down. But ice and sea level lag far behind temperature, and the Holocene climate envelope that civilization developed inside is not restored on any planning horizon a human institution can act on. By then, populations have redistributed toward buffered latitudes and elevations, and the geography of habitation looks materially different.
The honest verdict
The long view clarifies the near-term task. Because the floor is fixed and the danger window is close, the only lever with leverage is front-loading the 2020s–2030s: installing absorptive capacity while it is cheap, before the curves synchronize. Three things are beyond control — committed warming, demographic weight in hot zones, and default inequality. Everything else is allocation and timing.
Mitigation is not reset. It is navigation — choosing how wide the buffer is, and who is inside it, within a regime that is already locked in.