Climate Engineering & Carbon Capture:

Climate Engineering & Carbon Capture: The 2025 Playbook

A practical guide to transport choices, carbon removal pathways, and the policies that make them work

Intro

Climate engineering and carbon capture are not substitutes for cutting emissions. They are the safety net beneath an aggressive mitigation plan. The fastest route to a liveable climate still begins with using less fossil energy—especially in road transport and aviation—while rapidly scaling clean electricity.

The role for carbon removal is to address the residual emissions that remain difficult or impossible to abate in the near term, and to help draw down atmospheric CO₂ over time.This playbook is structured to follow that logic. We start with the choices that reduce demand for oil fuels right now: shifting from petrol and diesel cars to battery-electric vehicles (BEVs), deploying biomethane where it is genuinely waste‑based and well‑monitored, and piloting hydrogen fuel‑cell buses on duty cycles that are hard for batteries.

We then widen the lens to system levers—better public transport and fairer pricing for high‑end luxury emissions—before turning to three core carbon removal pathways: Direct Air Capture (DAC), Ocean Alkalinity Enhancement (OAE), and biochar.

Finally, we look at the policy architecture that determines what scales, what earns trust, and what should be left on the drawing board.

Throughout, we use a simple integrity filter for every claim and project:

Is it additional? Is it durable? Is it transparently measured? Is it community‑positive? If the answer to any of these is no, it is not climate‑grade.

1. Transport & Vehicles — ICE vs EVs vs Biogas vs Hydrogen (Swansea case)

Road transport is where climate engineering meets everyday life. The core decision is no longer whether electric cars work—they do—but how quickly to replace internal combustion engines (ICE) and how to decarbonise heavier vehicles that rack up mileage and require uptime.

Well‑to‑wheel (WTW) and life‑cycle views are essential. WTW tracks energy losses from primary energy to motion at the wheels. Life‑cycle analysis (LCA) adds manufacturing, maintenance, and end‑of‑life effects.

BEVs win on both, especially in countries with rapidly decarbonising grids. Even after accounting for battery manufacturing, typical drivers repay the manufacturing “carbon debt” within a modest period of use, after which every kilometre driven extends the advantage.

As grids continue to clean, the BEV advantage widens automatically.Hydrogen fuel‑cell electric vehicles (FCEVs) can be valuable for specific, demanding duty cycles—think buses or trucks with long daily routes, tight schedules, and depot refuelling—provided the hydrogen is produced with very low emissions and delivered efficiently.

The WTW efficiency of green hydrogen (electricity → electrolysis → compression → fuel cell → motor) is lower than charging a battery directly, so hydrogen makes the most sense where batteries are constrained by weight, range, or turnaround time.

Biomethane (also referred to as biogas upgraded to biomethane) is another near‑term lever, particularly for heavy goods vehicles. When derived from unavoidable organic waste streams and verified through robust certification, it can deliver material greenhouse‑gas savings versus diesel while making practical use of existing vehicle platforms.

The caveats matter: methane leakage, feedstock sustainability, and credible accounting must be monitored to ensure real‑world benefits.

Swansea’s planned hydrogen bus trial illustrates targeted deployment. A depot‑based fleet on defined routes, supported by a local refuelling hub, creates an operational test bed to gather evidence on cost, reliability, and emissions across the entire fuel pathway.

The trial should report openly on:

(1) the carbon intensity of hydrogen supplied,

(2) vehicle availability and maintenance profiles,

(3) passenger experience and air‑quality gains, and

(4) total cost of ownership compared with the best available battery‑electric alternatives.

What to prioritise now:

• Accelerate BEV uptake where charging access is feasible, with a focus on workplace and depot charging to reduce public‑charging pressure.

• Use biomethane where feedstocks are waste‑based and controls on methane slip are strong.

• Pilot hydrogen buses on appropriately demanding routes while publishing full fuel‑pathway data.

• Retire the oldest, dirtiest diesel vehicles first to maximise air‑quality benefits.

2. System Levers — Better Public Transport & Heavier Rules on Private Aerospace

Technology choices matter, but system design determines the scale of benefits. Two levers stand out: (A) improving public transport so it becomes the default for more trips, and (B) ensuring those with the most polluting, discretionary travel pay a fairer share for the damage.

Public transport improvements—bus franchising, metro electrification, simple ticketing, and reliable frequencies—unlock large, affordable emissions cuts by shifting passenger‑kilometres from private cars to buses and rail. The gains multiply when fleets are zero‑emission, cutting local nitrogen oxides and particulate matter alongside greenhouse gases.

For regions investing in networks like the South Wales Metro and modernised depots for electric or hydrogen buses, the benefits include quieter streets, more predictable journeys, and cleaner air.At the luxury end of travel, private jets emit disproportionately per passenger.

Tighter taxation and comprehensive carbon pricing—paired with sensible operational limits where good rail alternatives exist—send the right signal while raising funds that can be recycled into clean transport. Private space launches are a newer frontier.

Launch licensing that requires robust environmental assessment can address local noise, air‑quality, and stratospheric soot impacts, guiding technology choices and launch cadence before activity scales.

Policy priorities:

• Put integrated, reliable public transport first—then electrify buses and trains.

• Align private aviation with strict polluter‑pays principles and transparent accounting.

• Require environmental assessments for spaceports and launches, including monitoring plans and public reporting.

3. Direct Air Capture — Gigaton Projects Progress Report

Direct Air Capture (DAC) removes CO₂ from ambient air using chemical sorbents, then compresses and stores it—typically deep underground. Liquid systems absorb CO₂ into alkaline solutions; solid systems use functionalised materials such as amines or metal‑organic frameworks (MOFs).

Both approaches require energy for sorbent regeneration and CO₂ compression, making the source of heat and power central to climate performance.

Where we are now: early facilities are operating and larger plants are under construction, but the leap from thousands to millions—and eventually billions—of tonnes per year depends on four constraints:

(1) cost and learning curves,

(2) access to low‑carbon electricity and heat,

(3) reliable storage with transparent measurement, reporting, and verification (MRV), and

(4) siting near both clean energy and suitable geology or CO₂ transport networks.

Costs will fall with scale if deployments share common, modular designs and if supply chains mature for fans, contactors, sorbents, and heat systems. But energy dominates operating costs, so pairing DAC with curtailed renewables, geothermal, or other low‑carbon heat sources can be decisive.

For storage, deep saline formations and other geologic reservoirs provide durable options when injection, monitoring, and accounting are rigorous. Registries and purchase agreements that pay for verified removal—rather than for construction milestones—help focus attention on delivered climate value.

Checklist for credible DAC projects:

• Publish energy and heat intensity per tonne captured and share capacity‑factor data.

• Disclose the storage pathway, including monitoring plans and permanence assumptions.

• Use independent MRV and issue credits only on verified net removal.

• Build workforce and local‑benefit plans where facilities are sited.

4. Ocean Alkalinity Enhancement — Pilot Studies

Ocean Alkalinity Enhancement (OAE) increases seawater’s capacity to store carbon by raising alkalinity, which nudges carbonate chemistry toward higher dissolved inorganic carbon (DIC) at a given partial pressure of CO₂.

Candidate materials include magnesium hydroxide and certain silicate minerals; electrochemical methods can also produce alkaline streams. The science is well established in principle, but field deployment must answer practical questions about dosing, dispersion, durability, and ecological safety.

Pilot designs vary. Coastal tests might add carefully metered slurries in well‑mixed environments and monitor with high‑frequency sensors on buoys and gliders. Offshore pilots may experiment with subsurface dosing to enhance mixing and reduce visible turbidity.

Across all designs, MRV is the crux: tracking the alkalinity plume, estimating counterfactual conditions, and quantifying how long additional carbon remains stored. Ecological safeguards must be conservative at first—protecting local species, avoiding hotspots of over‑alkalinisation, and screening for impurities in input materials.

Good‑practice guardrails:

• Start small, monitor densely, and publish data openly.

• Use high‑purity materials and verify dissolution kinetics and trace‑metal profiles.

• Define ‘no‑harm’ ecological thresholds in advance and pause automatically if breached.

• Credit only the portion of carbon removal that is measured with confidence over a defined durability horizon.

5. Biochar — Supply Chains & Soil Health

Biochar is stable carbon made by heating biomass with limited oxygen (pyrolysis). Returning this porous, carbon‑rich material to soils can lock carbon away for decades to centuries while improving soil structure, water retention, and nutrient efficiency—benefits that depend on soil type, climate, and application rate.Quality and safety are non‑negotiable.

Feedstocks should be sustainable (ideally residues or wastes), and char should be tested for polycyclic aromatic hydrocarbons (PAHs), heavy metals, pH, and particle size distribution. Certification schemes and third‑party labs provide the guardrails to protect soils and buyers.

Supply chains come in two flavours. Mobile skid‑units can follow seasonal feedstocks and reduce transport emissions; centralised plants can maximise uptime, co‑generate useful heat or power, and produce consistent char.

Either way, rigorous documentation—feedstock origin, process conditions, yield, and application records—underpins MRV and credit issuance.

Agronomy must lead: target soils that benefit most (e.g., light, sandy soils with poor water retention), match char properties to soil pH, and trial appropriate doses before scaling.

Project design tips:

• Tie projects to local farms and green‑waste streams to cut logistics costs and build trust.

• Blend with composts or manures when appropriate to improve nutrient dynamics.

• Plan for long‑term monitoring to validate persistence and agronomic outcomes.

• Align claims strictly to measured carbon content and documented application.

6. Policy Landscape 2025 — Scaling High‑Integrity Negative Emissions

Policy is the throttle for negative emissions. Unlike mitigation policies that focus on reducing smokestack and tailpipe emissions, removal policies must centre additionality and durability—paying only for net, measured tonnes that remain out of the atmosphere for a long time.

The toolkit includes tax credits, carbon contracts for difference (which guarantee a strike price for verified removals), public procurement and advance purchase agreements, and clear standards for MRV and crediting.High‑integrity markets also require sound accounting.

Registries must prevent double‑counting, and any cross‑border transfers should follow transparent rules so that removals are retired once, for a defined purpose. Siting and environmental‑justice provisions ensure local communities share benefits and avoid undue burdens, from traffic and noise to water use.

A practical roadmap for 2025–2027:

• Build government and consortium procurement that pays for delivered removals with strict MRV.

• Stand up standard methodologies for DAC, OAE, and biochar with third‑party verification.

• Coordinate grid, pipeline, and storage infrastructure so projects can connect to clean energy and durable sinks.

• Require robust community engagement and benefit‑sharing before permits are issued.

Conclusion

There is no single fix. The credible path is a portfolio: cut demand first through better transport choices and system design; deploy carbon‑removal pathways that meet high bars for measurement and durability; and lock in policies that reward real climate value.

Readers, buyers, and policymakers can use one short checklist to navigate complexity:

• Additional — Would this removal or reduction have happened without this action?

• Durable — Will the carbon stay out of the atmosphere for as long as claimed?

• Measured — Is there transparent, third‑party‑verified MRV that covers the full system boundary?• Community‑positive — Are local people protected, heard, and benefiting?If any answer is no, pause and redesign.

If all are yes, scale with confidence.