Planetary Cooling Pathways: Scientific Scenarios for Returning to a Stable Climate State - Preprint

[Geoengineering News]

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=7319259

Authors: Hunter Hughes

20 August 2026

Abstract

Humanity has entered a dangerous climate overshoot regime in which achieving net‑zero emissions is no longer sufficient to restore Earth system stability. As the report states, “net‑zero halts additional greenhouse gas radiative forcing, but it stabilizes global temperatures at an elevated, dangerous plateau” . Even with full decarbonization, ocean thermal inertia, cryosphere disintegration, and carbon cycle hysteresis lock in centuries of warming and tipping‑element activation.

This research develops a century‑scale scientific architecture for Planetary Cooling—the intentional reduction of global mean surface temperature back toward the Holocene stability envelope (<1.0 °C, ~350 ppm CO₂). The analysis integrates Earth’s Energy Imbalance dynamics, ocean heat persistence, carbon cycle hysteresis, and multi‑vector interventions across both longwave and shortwave radiative pathways.

The core conclusion is that meaningful cooling within 50–100 years requires a Two‑Pronged Planetary Architecture:

Gigatonne‑Scale Carbon Dioxide Removal (CDR) delivering 15–22 Gt CO₂/yr by 2060–2080 through DACCS, Ocean Alkalinity Enhancement, Enhanced Rock Weathering, and biochar. This longwave restoration permanently reduces greenhouse forcing but operates on decadal–century timescales.

Temporary Solar Radiation Modification (SRM)—specifically multi‑latitude Stratospheric Aerosol Injection or Marine Cloud Brightening—to “shave” 0.5–0.8 °C of peak warming and prevent irreversible tipping‑element collapse while CDR scales. As the report notes, “SAI must never be deployed without binding, scaled CDR deployment” due to termination‑shock risks .

The report outlines a four‑phase planetary cooling timeline (2026–2100), governance requirements under a UN Planetary Cooling Oversight Council, and macroeconomic valuation showing >3.5:1 benefit‑cost ratios for structural CDR and >300:1 for SRM peak‑shaving.

Overall, the document argues that planetary cooling is not optional but physically required to avoid irreversible cryosphere loss, AMOC collapse, and multi‑system tipping cascades. It reframes climate action from “stopping warming” to actively restoring Earth’s radiative balance and long‑term habitability.

Source: SSRN