Which climate solutions
can actually cool the planet?
Cooling the Earth is a thermodynamic problem. Every intervention costs energy to build and operate. Cooling Return on Investment (CROI) is the ratio of heat removed from the Earth system to the energy invested to remove it — the physical filter that separates viable cooling strategies from impossible ones.
Cooling the planet is a thermodynamic problem.
Global warming is fundamentally the accumulation of thermal energy in the Earth system. To cool anything — a room, a body, a planet — heat must be absorbed, transported, and released into a lower-energy reservoir. For Earth, the only accessible reservoir is outer space.
Every step in that chain costs energy. Most climate metrics count tonnes of CO₂; CROI counts joules of heat removed per joule of energy invested. It is the physical filter that distinguishes climate solutions that can cool the planet from those that cannot.
Cooling Return on Investment, defined.
CROI is a dimensionless ratio: the total heat removed from the Earth system by an intervention over its entire lifetime, divided by the total energy required to build, deploy, operate and decommission it. It is the direct thermodynamic analogue of Energy Return on Investment (EROI).
1,500 terawatts of heat. 1 terawatt to work with.
Earth is currently accumulating roughly 1,500 TW of excess heat from the greenhouse effect. Total human energy consumption across every sector is only ~18 TW. At most, humanity could realistically redirect ~1 TW to active cooling without collapsing other essential systems.
This yields a single unforgiving requirement: any viable planetary cooling strategy must operate at a lifetime-averaged CROI of at least ~1,500, with a practical target range of 1,000 – 3,000. Anything below this threshold fails before it begins.
Continuous excess heat accumulating in the Earth system from the greenhouse effect. This is the heat that must be removed to stabilise the climate.
All of civilisation — food, water, transport, industry, buildings, hospitals, digital infrastructure — runs on roughly 18 TW of continuous primary energy.
The plausible upper bound of energy humanity could redirect toward active planetary cooling without collapsing other essential sectors.
Practical target range: 1,000 – 3,000. Any intervention with a lifetime-averaged CROI below this range cannot, by the laws of physics, materially cool the planet — regardless of how much capital, land or political support it receives.
Which technologies cross the CROI threshold?
Comparing candidate climate interventions by their lifetime-averaged CROI, on a logarithmic scale. Only passive, material-light, high-albedo and radiative-cooling strategies reach the physical threshold required to meaningfully reduce Earth's Energy Imbalance.
These values represent order-of-magnitude estimates based on the current MEER Cooling Return on Investment framework. Actual performance depends on engineering design, material selection, manufacturing energy, deployment scale, maintenance requirements and operational lifetime. The viability zone (≈ 1,000–3,000) is itself a range — the exact threshold depends on assumptions including available global energy, deployment scale, embodied energy, operational lifetime and engineering efficiency. Research continues to refine these estimates.
Values vary with material selection, manufacturing energy, modular design and operational lifetime.
Emits thermal infrared through the 8–13 µm atmospheric window directly to space. Performance depends on formulation, thickness and durability.
Performance depends on reflectivity, embodied energy, durability and deployment scale. Higher-performance formulations can approach the viability zone.
Current values remain preliminary pending further engineering validation. Reflective floating elements can extend into the viability zone at scale.
Valuable local co-benefits, but slow, reversible and geographically limited. Below the estimated planetary cooling range.
Sorbent regeneration consumes far more energy than the resulting cooling recovers under current CROI assumptions.
A high-CROI system repays its energy debt almost immediately.
Building a passive reflective system costs a fixed amount of embodied energy (Ein) up front. From the moment it is deployed it begins removing heat (Qout). For a system with CROI ≈ 1,500 the initial energy debt is repaid in a matter of weeks — the remainder of the lifetime is pure net heat removal.
For a passive reflective system with lifetime-averaged CROI ≈ 1,500 over 15 years, the initial embodied-energy debt is repaid within weeks of deployment. Everything afterwards is net heat removal — which is why passive, material-light systems are the only class of intervention that can address Earth's Energy Imbalance in real time.
Passive cooling in the world.
Indicative CROI ranges for four categories of passive reflective deployment. Actual values depend on materials, siting, insolation, and lifetime — these are illustrative rather than measurements of any single installation.
School roof, Sierra Leone
A community school roof coated with high-albedo material. Almost no operating energy; cooling begins on day one and continues through every daylight hour of the lifetime.
Illustrative ranges derived from the MEER CROI framework; not measurements of a specific installation.
CROI is one lens among many.
CROI does not replace existing climate metrics — it complements them. Each answers a different question about a technology's real-world value. CROI is the only one that directly answers: can this intervention actually cool the planet?
Embodied carbon
Emissions locked into materials & construction.
Life-cycle assessment
Full environmental cost from cradle to grave.
Energy Return on Investment (EROI)
Energy delivered by a source per unit of energy invested.
Avoided emissions
Greenhouse gases prevented by using the technology.
Radiative forcing (W/m²)
Change in Earth's net radiation from a perturbation.
Heat reduction
Measured surface or air temperature drop.
Resilience
Ability to keep working through heat events & grid stress.
CROI
Heat removed from the Earth system per unit of energy invested.
References & further reading
CROI figures on this page are drawn from MEER's internal CROI framework. EEI values are consistent with the peer-reviewed literature cited below.
- Tao, Y. — MEER CROI framework (internal research, 2026)
- Loeb et al. (2021) — Satellite and ocean data reveal rapidly rising Earth's Energy Imbalance (GRL)
- Hansen et al. (2023) — Global warming in the pipeline
- Raman et al. (2014) — Passive radiative cooling below ambient (Nature)
- IPCC AR6 WG1 — Chapter 7: The Earth's Energy Budget
Cooling Impact Framework
MEER is developing an open, peer-reviewable methodology for estimating lifecycle CROI across passive cooling technologies — with transparent assumptions on embodied energy, albedo, effective radiative flux and lifetime.
Related science
Earth's Energy Balance
The 1,500 TW imbalance driving planetary heating.
Understanding Albedo
Why reflective surfaces cool the planet.
Surface Reflection
Turning sunlight away before it becomes heat.
Radiative Cooling
Emitting heat directly to the cold sky.
Climate Tipping Points
Why cooling matters urgently.
Environmental Sensors
How we verify real-world cooling.