The Climate Change Committee’s recent adaptation framing rests on a simple but powerful claim:
Britain was built for a climate that “no longer exists”, and therefore public policy must now be reorganised around climate risks projected for 2°C of global warming by mid-century and, at the high end, 4°C by 2100. No serious policy-maker should ignore flood risk, heat risk, drought risk, infrastructure vulnerability or water stress. Practical resilience is necessary.
But the CCC’s approach raises a serious question of scientific proportionality: are high-end model scenarios being treated as risk-management tools, or are they quietly becoming the policy baseline?
The problem begins with UKCP18.
UKCP18 is a major Met Office climate-projection suite designed to help decision-makers assess exposure to future climate risk.
However, the most spatially detailed UKCP18 regional and local products are heavily tied to RCP8.5, the high-emissions pathway in which greenhouse gas emissions continue to grow largely unmitigated.
In Met Office guidance, RCP8.5 is associated with a best-estimate global temperature rise of about 4.3°C by 2100. The CCC’s own report uses RCP4.5 for its 2050s 2°C framing and RCP8.5 for its 2100 4°C framing in parts of the analysis. It also presents 4°C warming by 2100 as a possibility that should be considered in long-term planning.
That may sound prudent, but the scientific context has changed. RCP8.5 and its later equivalent SSP5-8.5 are no longer widely regarded as credible “business as usual” pathways. Recent scenario work for CMIP7 explicitly recognises that the former high-end scenario has become implausible for the 21st century because of observed emissions trends, the growth of climate policy and changes in the global energy system. Even mainstream analysts who strongly support climate action now argue that current-policy warming is more likely to sit below the old RCP8.5-type trajectory, with central estimates closer to the mid-range rather than the extreme high-end pathway.
This matters because scenarios are not forecasts. They are conditional exercises: “if the world follows this pathway, then these modelled consequences may follow.” But when an extreme pathway is used repeatedly in public-facing policy documents, local authority guidance, infrastructure planning, flood-risk mapping, housing standards, public-health planning and economic-cost estimates, it can become psychologically and administratively converted into an expected future. That is how a low-probability scenario becomes a governing assumption.
There is a second, deeper scientific issue. Conventional climate-policy modelling often gives the impression that climate response is essentially a linear function of greenhouse-gas forcing, moderated by feedbacks. Yet the Earth’s climate is not a passive CO₂ control knob. It is a dynamic heat-engine system involving solar absorption, albedo, clouds, water vapour, convection, thunderstorms, ocean circulation, latent heat and poleward energy transport.
The recent Constructal climate model proposed by Willis Eschenbach is not final proof of a low climate sensitivity, but it is an important challenge model.
It treats climate as a self-organising flow system, using albedo and greenhouse parameters derived from satellite observations, and reports that a simple model can reproduce broad hot-zone and cold-zone temperature behaviour using far fewer assumptions than conventional general circulation models. Its estimated equilibrium climate sensitivity is around 1.1°C per CO₂ doubling, far below the IPCC’s central estimate.
That figure should not be adopted uncritically. But neither should it be ignored.
Its significance is not merely the exact number. Its significance is that it demonstrates a plausible alternative physical framing: the climate system may be more actively self-regulating than policy models assume. If albedo, cloud formation, convective timing, water-vapour behaviour and poleward heat transport provide stronger stabilising feedbacks than current models represent, then projections derived from high-sensitivity, high-emissions pathways will exaggerate future risk.
The CCC’s adaptation case therefore needs a stronger uncertainty discipline. It should clearly separate observed climate change from modelled future change. It should distinguish central scenarios from upper-tail scenarios. It should show which recommendations survive under lower-sensitivity or mid-range emissions assumptions, and which depend materially on high-end RCP8.5-style outcomes. It should also disclose where local UKCP18 products are constrained by RCP8.5 availability and therefore may not represent a balanced range of plausible futures.
This is not an argument against sensible adaptation. Flood resilience, drainage maintenance, reservoir capacity, urban shade, care-home cooling, water efficiency and infrastructure hardening can all be justified as practical resilience measures where costs are proportionate and benefits are local, measurable and robust. But it is an argument against using uncertain high-end projections as a mandate for open-ended statutory duties, centrally directed spending, planning restrictions or wider Net Zero policy acceleration without transparent probability-weighting.
A better policy test would be simple.
First, identify the observed hazard using real-world UK data.
Second, test the proposed intervention against a central scenario, not only a worst-case pathway.
Third, run sensitivity tests using lower and higher climate sensitivity assumptions.
Fourth, publish a cost-benefit case showing whether the measure remains justified if warming tracks closer to 2–3°C by 2100 rather than 4°C. Fifth, avoid using RCP8.5-derived outputs as public-facing evidence unless they are clearly labelled as low-probability, high-impact stress tests.
The CCC is right that the UK should prepare for weather risk.
But preparation is not the same as panic, and resilience is not the same as model-driven central planning. Public policy must be grounded in measured hazards, realistic scenarios, engineering practicality and democratic consent.
Climate is not a simple CO₂ control knob. It is a dynamic heat-engine system with powerful self-regulating mechanisms. Policy should reflect that uncertainty, not conceal it behind the apparent precision of modelled projections.
The conclusion is clear:
The CCC’s adaptation advice should be reframed from “prepare for modelled climate futures” to “build proportionate resilience against observed and plausibly forecast risks.” RCP8.5 may have a limited role as a stress-test scenario, but it should not be allowed to function as the hidden backbone of UK public policy.
Shane Oxer — Campaigner for fairer and affordable energy
SAY NO TO THE DESTRUCTION OF OUR LAND 
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