Time Left to Critical Climate Feedback/Loops: Annual Solar Geoengineering-PLUS, Pathways to Planetary Self-Cooling

[Geoengineering News]

https://www.mdpi.com/2225-1154/14/2/37

Authors: Alec Feinberg

01 February 2026

https://doi.org/10.3390/cli14020037

Highlights

Modeling indicates that self-heating feedback loops are likely to reach a mitigation critical 50% threshold of global warming between 2075 and 2125 if no Solar Geoengineering is applied, making reversing global warming overly difficult, and tipping points are anticipated.

Annual Solar Geoengineering-PLUS pathways are introduced to counter high-amplification regions through Earth Brightening, Arctic Stratospheric Aerosol Injection, and L1 Space Sunshading. This approach also focuses on amplified feedback regions in the Arctic and the tropics, reducing local chain reactions by promoting self-cooling negative feedback loops.

The mitigation difficulty and cost rate (MDCR) is estimated to increase by 1.33–1.5% per year, so that by 2100, without intervention, the increase will be ≈100% of today’s baseline, an unsustainable mitigation critical threshold.

L1 Space Sunshading (SS) area efficiency assessments show that the required shading area is ≈32× lower than prior flawed estimates, and ≈1600× lower when using the ASG+Ps method. Given the long-term risks to civilization, development in this area should be treated as an urgent priority for space agencies.

Simple Summary

Global warming is entering a critical phase where the planet is beginning to heat itself through feedback loops, chain reactions that amplify warming. Human-caused warming is increased by nature’s feedback problems, like snow and ice melting, which makes the planet hotter as we lose reflectivity. But as the planet loses reflectivity and warms, more snow and ice melt, and this is called a feedback loop. There are a number of self-heating feedback loops, making the system hotter and harder to control. This study estimates that within 50 to 100 years, these self-reinforcing feedback loops could amplify over half of all global warming, reaching a mitigation critical point beyond which reversal may be nearly impossible. While reducing CO2 emissions remains essential, there is poor progress, and these chain-reactive heating loops continue to increase. Because warming comes from sunlight, Solar Geoengineering (SG) can be used, which reduces solar warming. It includes Earth Brightening and feasible Space Sunshading that are estimated to be 14–15 times stronger than CO2 removal per unit of energy. The moderate Annual SG-PLUS pathways proposed here, which include targeted high feedback loop regions like the Arctic and the tropics, would buy crucial time and help excite reverse feedback loop chain reactions, encouraging the planet to self-cool alongside other mitigation methods. Results also indicate that space agencies like NASA and SpaceX could safely and feasibly help substantially in climate mitigation. If we delay, the mitigation difficulty and its cost are estimated to increase by about 1.5% each year. SG activities have the potential to lessen the severe danger that climate change poses to society, saving trillions in damages.

Abstract

Global warming (GW) contributions from feedbacks and feedback loops are projected to rise from ≈54% (loops: 29%) in 2024 to ≈71% (loops: 50%) under faltering RCP pathways without Solar Geoengineering (SG) by about 2100. A critical threshold, RCP_Critical, defined as the point at which feedback loops account for more than half of GW, is projected to occur between 2075 and 2125. Beyond this point, reversing warming becomes severely constrained, and climate tipping points become more likely. From these trends, an average mitigation difficulty and cost increase rate (MDCR) of ≈1.33–1.5% per year is estimated. By 2100, absent mitigation, the effort required to offset global warming would roughly double relative to today, approaching an unsustainable mitigation critical threshold. Current feedback levels may already be driving nonlinear warming behavior. These diagnostic estimates align with three key indicators: a minimum-feedback baseline from 1870, an equilibrium climate sensitivity (ECS) range of 3.1 °C–4.3 °C (potentially reached by ≈2082), and consistency with IPCC AR6 confidence bounds. In response, this study proposes Annual Solar Geoengineering-PLUS pathways (ASG+Ps) as supplemental measures. These include Earth Brightening, targeted Arctic Stratospheric Aerosol Injection (SAI), and feasible L1 Space Sunshade systems designed to reduce feedback amplification and extend mitigation timelines. The “PLUS” component refers to the use of increased mitigation levels with a focus on high-amplification regions, particularly the Arctic and the tropics, to help reverse local feedbacks and promote negative feedback loops. These moderate ASG+P pathways directly address AR6 concerns while avoiding many governance challenges of full-scale SG. ASG+Ps are less controversial and provide ≈14× stronger cooling potential per Wm−2 than Carbon Dioxide Removal (CDR), while allowing variable regional targeting. Meanwhile, RCP2.6 has already been missed, placing RCP4.5 and RCP6 at risk. In 2024, atmospheric CO2 rose by ≈23 Gt (≈3 ppm), while forest tree losses exceeded afforestation gains by 2×, yielding a 2 GtCO2 sink loss, further diminishing CDR’s effectiveness. Declines in planetary albedo since 1998 continue to amplify warming. Urbanization accounts for roughly 13% of total surface GW, affecting 60% of the population, underscoring the mitigation potential of urban Earth Brightening. New results here also show major Space Sunshading area reductions, at ≈32× less than prior flawed estimates (detailed here) and ≈1600× less under the ASG+P method, substantially improving feasibility and the importance of space agencies’ needed mitigation role. A coordinated global ASG+P strategy, supported by IPCC working groups and space agencies like NASA/SpaceX, are needed to provide a critical supplemental pathway for climate stabilization. Given the shrinking intervention window, rising MDCR, and the escalating risks to civilization, prioritizing timely work in this area is essential; the investment is minor compared to the trillions in climate financial damages that could be avoided.

Source: MDPI