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Near-term Global Cooling: What’s the Plan?

Ron Baiman

Co-Founder and Convening Coordinator

Healthy Planet Action Coalition (HPAC)

rpbaiman@gmail.com

How Climate Intervention can Safely, Effectively, Quickly and Inexpensively Cool the Planet

Healthy Planet Action Coalition

NYC Climate Week Event

Sep. 26, 2025

The Brooklyn Society for Ethical Culture

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Accessing the HPAC Urgent Response Working Group Near-term Climate Cooling Chart

Scroll to the lower middle of the landing (front) page of the HPAC website: www.healthyplanetaction.org and move your cursor to the: “See the full “Plan” matrix with expanded labels here” button.
And click after it switches to a white background as shown below:

This will take you to a google spreadsheet version of the “Matrix of Ranked Priority Cooling Strategies” that is slide 8 of the HPAC website power point presentation (see also next slide 5 of this PPP below) with 9 slides starting with slides 3-4 below, that can be scrolled through by repeated clicking on the slides or using the scroll bar.

The HPAC Perspective on the Situation that We Face

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The HPAC Perspective on the Situation that We Face

Given that:

“Dangerous anthropogenic interference with the climate system” has begun and further warming, extreme events and sea level rise will far exceed the potential for adaptation;
Reaching net zero CO₂ emissions is proving difficult and will likely take many decades;
Until CO₂ emissions are down by about 90%, carbon dioxide removal (CDR), ending deforestation, and nature-based approaches can only reduce the rate of increase of global temperature, not cool or reduce global temperature, unless the potential for ocean iron fertilization is greatly underestimated;

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The HPAC Perspective on the Situation that We Face

(Continued)

Sharp reductions in emissions of methane, black carbon and other short-lived species is a potential path to off-setting about 0.5°C of temperature increase;
But only climate intervention with volcano-imitating stratospheric aerosols started soon, possibly augmented by atmospheric methane oxidation, have the potential to exert up to a 0.5 to 1.0 C reduction in global temperature influence by 2050 and pull the climate back toward average 20^th century conditions.

HPAC urges international negotiators to adopt and implement a triad-based approach as described in the following slides.

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	Links describe columns and rows, darker colors have greater benefit
	Methods With the Highest Plausible Effect				Priority Ordering Based on Effectiveness:
		1	2	3	4	5	6	7	8	9	10	11
	Method or strategy	Type	Continuing, or once	2050 potential	Realistic time frame	Risk compared to non-use	Potential 2050 magnitude	Cost/benefit	Readiness	Scientific confidence	Beneficial Indirect effects	Current level of policy
1	Reduce methane emissions	Warming reduction	Once and done	Substantial	Years <= 10	Negligible	Up to 0.5 C	Moderate	High	High, cause of warming	High	High
2	High-latitude stratospheric aerosols	Sunlight reflection	Continuing	Substantial	Years <= 15	Small	Up to 0.5 C	High	Medium	Modest, natural analog	Moderate	Low
3	Global stratospheric aerosols	Sunlight reflection	Continuing	Substantial	Years <= 20	Small	Up to 1.5 C	High	Low	Modest, natural analog	Moderate	Low
4	Catalytic methane reduction	Warming reduction	Continuing	Substantial	Years <= 20	Small	Up to 0.5 C	Moderate	Low	Low, proven in laboratory	Moderate	Negligible
	Methods with the Potential to have a Modest Effect by 2050

5	Ease ship fuel regulations	Sunlight reflection	Continuing	Possible	Years <= 5	Small	Up to 0.2 C	High	High	High, recent history	Moderate	Low
6	Reduce black carbon emissions	Warming reduction	Once and done	Possible	Years <= 10	Negligible	Up to 0.2 C	Moderate	High	High, cause of warming	High	Modest
7	Tropospheric aerosols	Sunlight reflection	Continuing	Possible	Years <= 20	Moderate	Up to 0.2 C	Moderate	Medium	Low, past history	Moderate	Negligible
8	Marine cloud brightening	Sunlight reflection	Continuing	Possible	Years <= 20	Moderate	Up to 0.2 C	Moderate	Low, at global scale	Low, natural analog	Moderate	Low
	Methods that are Likely to Have a Minor Effect by 2050

9	Forestation strategies	Increased sequestration	Once and done	Unlikely	Years <= 20	Negligible	Up to 0.2 C	Low	Medium	Modest, ecological examples	High	Modest
10	Space mirrors	Sunlight reflection	Continuing	Very Unlikely	Years > 20	Small	Unknown	Unknown	Very Low	Modest, theoretical	Moderate	Negligible

Matrix of Ranked Priority Cooling Strategies

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Slide 8: Method evaluation criteria in columns E-M

E. Potential for plausible 2050 deployment in combination with other methods to contribute to reduction of risk of crossing tipping points

F. Realistic time to significant at-scale deployment

G. Risk of adverse consequences compared to non-use

H. Potential magnitude of near-term global/hemispheric scale climate cooling from plausible deployment by 2050 (relative to global warming by 2050 without near-term cooling)

I. Benefits of reduced global/hemispheric warming relative to projected cost

J. Technological Readiness Level

K. Current level of scientific confidence and efficacy compared to non-use

L. Projected level of additional beneficial health and ecological effects (not directly related to cooling, or more related to local rather than global cooling impacts)

M. Current level of policy consideration

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Slide 8: Row Ordering Based on Prioritizing Near-Term Cooling Methods

We then rank order the methods based on prioritizing the following criteria for relative importance in addressing the harm from not urgently cooling the globe by 2050;

First based on tipping point risk reduction (E)
Within this by full-scale deployment time (F)
Within this by (natural science) risks compared to non-use (G)
Within this by 2050 magnitude of cooling relative to no-intervention (H)

This ranking procedure produces the near-term climate cooling method (row) ordering displayed in the slide 5 table above (and slide 8 of the Near-Term Cooling power point near the bottom of the landing page of the HPAC website) and slide 9 below.

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Slide 8 Grouping of Methods Based on� Tipping Point Risk and Climate Harm Reduction

Methods that could substantially reduce climate tipping point risk and address near-term harm from global warming

Reducing methane emissions
Polar stratospheric aerosol injection
Global stratospheric aerosol injection
Catalytic reduction of atmospheric methane

Methods likely to have a modest global warming harm reduction and tipping risk reduction impact

Easing IMO shipping fuel regulations in the high seas
Reducing black carbon emissions
Non-fossil fuel generated benign tropospheric aerosol injection
Marine cloud brightening

Methods likely to have minor to no warming harm reduction and tipping risk reduction impact

Reforestation/afforestation and other means of increasing ecosystem carbon dioxide uptake
Place mirrors (or sunshades) in high-Earth orbit to reduce absorption of incoming solar radiation

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Conclusions

We need to quickly deploy climate cooling as overshoot time and consequent risk of crossing tipping points (some irreversible) (Futerman et al. 2025) and large-scale climate and ecosystem harm will be longer the longer we wait (Boselius et al. 2024).
Because of of mixing and very high leverage on the stratosphere, at the very top of the Earth’s atmosphere, the most important near-term cooling method by far is Stratospheric Aerosol Injection (SAI).
Due the way stratospheric currents work it appears that the only way balanced gradual piloting and scale-up of regionally targeted “sub-scale” SAI can have a measurable signal is to start in the polar regions (Baiman et al. 2024 p. 15-16)
Methane emissions reduction and drawdown is best for quick cooling that also serves to reduce GHG emissions.
The above methods should be supplemented by relaxing International Maritime Organization (IMO cooling “termination shock” (Baiman et al. 2024a) and black carbon Greenhouse particle emissions reduction methods that would have a quick modest cooling impact, and cool and improve human health, respectively,
And by methods like Tropospheric Aerosol Injection (TAI) perhaps with Iron Salt Aerosol (ISA) and Marine Cloud Brightening (MCB) that could have a modest global cooling impact through targeted regional deployment.
Methods designed to increase ecological uptake like reforestation/afforestation could have a minor cooling impact by 2050 and would be unlikely to significantly reduce tipping point risk, and likewise space mirror deployment is not realistically possible by 2050.

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Coordination and Governance

At least three differently motivated near-term deployment governance scenarios seem plausible:

A coalition of willing nations and indigenous Arctic peoples, like the International Space Station piloting polar SAI to “saving polar ecosystems” like the “saving the Great Barrier Reef” MCB effort in Australia.
Collaborative international effort under the auspices of relevant UN bodies,
Self-interested actions by a “geopolitical power” such as the: US, China, Brazil, India, or combinations of these and allies, or some other consortium of nations.

It appears that only five aerospace companies based in these countries have the current capacity to produce jet engines for stratospheric lofting of large payloads (Horton 2025), though the US currently has planes that could begin doing this in polar regions where the stratosphere is lower (Smith et al. 2024).

All three scenarios would likely start modestly and be increased over time as confidence is gained that global-scale SAI deployment would be both largely beneficial and essential to return GSAT to <1°C by 2050.

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