On a Razor's Edge: A Narrow Path to 1.5˚C

In 2017, One Earth and collaborators were tasked with developing a global 1.5˚C pathway without the continued use of fossil fuels or relying on unproven, and increasingly unreliable, technologies like engineered carbon capture. Recent developments have cast doubt on the feasibility of staying below this target due to the bounce-back of emissions after the COVID-19 dip and an updated carbon budget based on more accurate Earth system modeling.

As every fraction of warming matters, all hope is not lost if we surpass 1.5˚C. The closer we can stay to this target, the better chance we have at securing a future that leaves room for thriving societies and functioning ecosystems. The story of climate action is not just about avoiding collapse; it is about building a better world. We therefore assess 1.5 °C as a practical and aspirational constraint to guide policy and deployment. Our “razor’s edge” scenario shows that while the path is narrow, it remains open.

Our updated high-ambition scenario is one of the first to incorporate post-COVID emissions, real-world energy deployment trends, and updated carbon budgets while transitioning to 100% clean, renewable energy and using only natural carbon dioxide removal. The model finds a narrow path with a limited overshoot (~1.6 °C in the 2035–2055 window) and a return toward ~1.4 °C by century’s end if investments in renewables, efficiency, and restoration scale rapidly.

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Why the 1.5 °C Target Is in Question

• Shrinking carbon budget: New Earth system modeling (accounting for aerosols, permafrost, and feedbacks) has reduced the amount of CO₂ humanity can emit while staying near 1.5 °C.
• Emissions rebound: After the brief COVID-19 dip, fossil fuel emissions returned to record highs and have plateaued, rather than declining steeply as many models assumed.
• Limited carbon removal: Recent studies show that nature-based removal (like reforestation) is more constrained than older models suggested once competing land uses are considered.

Together, these developments make the 1.5 °C pathway far narrower than many earlier scenarios assumed.

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The One Earth ‘razor’s edge’ Climate Model

The One Earth ‘razor’s edge’ Climate Model  (OEreCM), incorporates the latest real economy data on fossil fuel and renewable energy deployments between 2019-2024 to build a realistic, yet ambitious scenario to decarbonize the global economy across all sectors by 2055. The model has four phases: ‘Warm-up’ (2025-2030); ‘Low-hanging Fruit’ (2030-2040); ‘Ramp-up’ (2040-2050); and ‘Deep Decarbonization’ (2050-2055). Our model reaches complete decarbonization in 2055 by supplying 403EJ in final energy (17% increase from 2019) met almost entirely by renewable energy sources, and relying on over 190EJ of avoided energy demand through energy efficiency measures. Additionally, to achieve the long-term 1.5°C goal of the Paris Climate Agreement, 200 GtCO2 of nature-based carbon dioxide removal is required between 2025 and 2055 (with a long tail of additional removal through 2100).

In our model, energy and industry CO₂ peak in 2024 and edge downward from 2025. From that inflection point, progress arrives in four phases that use today’s momentum (surging renewables, fast EV/heat-pump adoption, improving efficiency) to push into harder sectors later—without leaning on speculative engineered removal.

‘Warm-up’ (2025-2030)

Our near-term priority is to lock in the post-2024 peak and turn it into a durable decline. This phase is about building momentum and ensuring that nearly all new power capacity comes from renewables while coal plant retirements accelerate, and grids and storage capacity scale to handle more wind and solar. On the demand side, mass EV and heat pump adoption should lead the way in delivering visible efficiency gains while increasing quality of life. During this phase, land-use restrictions need to be tightened in parallel to rapidly reduce deforestation and peat loss, setting up a full phase out by 2035.

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What this feels like

• Cleaner air, quieter streets: Fewer fossil fuel cars and coal stacks; air quality improves first in cities.
• Lower, steadier bills over time: Efficiency upgrades and heat pumps start flattening household energy costs.
• Local job creation: Construction, grid upgrades, rooftop solar, building retrofits, reforestation, and ecosystem restoration.

How it happens

• Speed up grid interconnections and transmission with regional planning and streamlined permitting.
• Lock in coal retirement schedules; end new unabated coal.
• Scale EV and heat-pump incentives, building codes (electric-ready), and appliance standards.
• Enforce zero-deforestation supply chains; fund peatland protection and restoration.
• Set storage procurement targets and flexible-demand programs (e.g., demand response, smart charging).

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‘Low-hanging Fruit’ (2030-2040)

This decade delivers the fastest, least-cost cuts by scaling mature technology. Fossil fuel use during this decade falls roughly in half by 2040 as widespread energy efficiency measures are deployed across all sectors and electrification spreads across transport, buildings, and lower-temperature industries. On land, deforestation and peat loss hits zero by 2035, and nature-based removal scales within ecological and social limits. What we achieve during this phase will determine whether the overshoot remains limited and temporary.

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What this feels like

• Quieter, cleaner transport: Electric cars and buses and the expansion of commuter rail options; electric charging is easy and ubiquitous.
• Health gains: Fewer asthma and pollution-related illnesses; more comfortable homes from efficient retrofits and heat pumps.
• Community benefits: Restored forests, mangroves, and peatlands providing flood protection, biodiversity, and livelihoods.

How it happens

• Zero-emission vehicle sales standards and charging/hydrogen corridor build-outs.
• Building performance standards, deep retrofit programs, heat-pump and induction incentives at scale.
• Time-of-use rates and virtual power plants to shift demand and integrate more renewables.
• Methane regulations across energy, waste, and agriculture.
• Guardrails for nature-based removal: tenure rights, biodiversity safeguards, high-integrity MRV, no displacement of food production.

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‘Ramp-up’ (2040-2050)

With the easy wins secured, the system turns to hard-to-abate sectors. High-temperature industry leans on electric process heat where feasible, with clean hydrogen and sustainable e-fuels beginning to power sectors that aren’t easily electrified. Road and rail transport become almost fully electric, while aviation and shipping increase efficiency and rely on “drop-in” biofuels, hydrogen fuel, and e-fuels. By this phase, grids, storage, flexible demand, and transmission improvements are mature, and renewables provide the overwhelming share of generation. During this phase, the global mean temperature hovers near the ~1.6 °C overshoot (2035–2055), while the return path is established by sustained cuts and continued land stewardship.

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What this feels like

• Cleaner industrial towns: First-of-a-kind (then standard) green steel, low-carbon cement, and chemical plants.
• Ports and airports get cleaner: Ships plug into the grid at shore; cargo movers and airport ground gear go electric; planes use electric gate power and cooling. For long-haul, cleaner e-fuels begin use and cut local soot and sulfur.
• Skilled jobs & new supply chains: Electrolyzers, e-fuel synthesis, high-temp electric equipment, recycling and remanufacturing.

How it happens

• Green public procurement for steel, cement, fuels pulls markets forward.
• Fuel standards for aviation and shipping that ratchet up sustainable and e-fuel blends.
• Critical-minerals strategy: recycling mandates, design-for-reuse, and responsible sourcing standards are implemented
• Build long-term energy storage, string new high-capacity lines between regions so we can share clean power when and where it’s needed, and modernize neighborhood grids so they stay reliable and can handle rooftop solar and EV charging.
• Workforce transition programs for fossil-dependent regions (training, pensions, local reinvestment).

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‘Deep Decarbonization’ (2050-2055)

Residual emissions are driven toward zero. By 2055, energy and industry CO₂ are down ~98% vs. 2025, and fossil energy is phased out for end use. Roughly 70% of total final energy is renewable electricity (mostly wind and solar); heat pumps and renewable heat dominate buildings and industry; hydrogen and e-fuels cover the last hard niches. Transport energy shrinks from 121.5 EJ (2019) → 47.1 EJ (2055) as efficient EVs take over road travel and e-fuels support aviation and shipping. With  around 200 GtCO₂ of nature-based removal by 2055 (and ~440 GtCO₂ by 2100), the system bends back toward 1.4 °C by century’s end, with a 2025–2100 average near 1.5 °C—provided deployment and protection stay on pace.

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What this feels like

• Stable, resilient energy: Bills less exposed to fuel price spikes; widespread demand flexibility keeps the lights on.
• Healthy places: Much cleaner air and water; reclaimed lands and brownfields repurposed for community use.
• Economic renewal: New industries anchored in clean power hubs; restored ecosystems supporting tourism, fisheries, and agriculture.

How it happens

• Sunset clauses for remaining fossil uses; strict carbon-intensity standards for any residual industrial processes.
• Limit CCS to high-value, process-emissions niches with high capture performance and transparent MRV.
• High-integrity, long-term finance for nature-based removal and stewardship through 2100.
• Decommissioning plans for fossil infrastructure and mine reclamation tied to local job programs.
• Equity-focused just transition funds and place-based development to ensure communities benefit.

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Resulting Emissions and Cumulative Atmospheric Carbon Dioxide

This figure shows annual emissions by source, net emissions, and the running total since 2020 alongside probabilities of remaining below 1.5°C as a function of cumulative GtCO2. Net emissions become negative in the mid-2040s, causing cumulative CO₂ to peak in 2043 and fall thereafter, allowing temperatures to bend down after the ~1.6 °C overshoot. The trajectory depends on three major actions achieved in parallel: a fast fossil phase-down, a surge in renewables and energy efficiency, and global protection and restoration of our ecosystems.

The rapid transition needed to secure a better future may exist along a razor’s edge, but there is hope in the fact that renewables have ramped up at a far greater pace than previously anticipated and are on track to providing nearly 100% of new installed power capacity well before 2030. It’s up to us to build on that momentum through significant investments in renewable infrastructure and energy efficiency, and fostering the major potential of nature-based carbon removal by rapidly increasing afforestation, reforestation, and revegetation (ARR) efforts through nature conservation and stewardship. If we can walk this narrow path, we can do more than avoid harm;, we can build thriving societies with cleaner air, healthier cities, and flourishing ecosystems.

Explore the One Earth razor's edge Climate Model