Climate Risk Transmission: How Climate Moves From Hazard to Balance Sheet

Climate risk rarely appears on an insurer’s balance sheet labelled as climate risk. It arrives as an elevated catastrophe loss ratio, a reinsurance renewal that costs 22% more than the prior year, a downgrade on a corporate bond held in the asset portfolio, or a court award that extends liability to an underwriting class that never priced for it. The original driver is climate; the balance sheet line item is market risk, underwriting risk, credit risk, or operational risk. Between the driver and the line item sits a transmission channel — and the channel is what actuaries need to model, not the driver itself.

This matters because the standard climate-risk taxonomy — physical, transition, legal/reputational — is useful for framing but not for pricing. An insurer cannot take “physical risk” and attach capital to it. What the insurer can do is trace the chain from a specific physical event, through the economic and financial mechanisms by which it transmits, to the specific contract cash flow or asset holding it affects. That trace is the transmission channel.

flowchart LR
    C1[Physical Risk] --> M1[Micro Channel:<br/>Firms and Households]
    C2[Transition Risk] --> M1
    C3[Legal / Reputational Risk] --> M1
    C1 --> M2[Macro Channel:<br/>Economy and Markets]
    C2 --> M2
    C3 --> M2
    M1 --> BS1[Underwriting Risk]
    M1 --> BS2[Credit Risk]
    M2 --> BS3[Market Risk]
    M2 --> BS4[Liquidity Risk]
    M1 --> BS5[Operational Risk]

    style C1 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0
    style C2 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0
    style C3 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0
    style M1 fill:#0A0F1E,stroke:#C9A84C,color:#F0F0F0
    style M2 fill:#0A0F1E,stroke:#C9A84C,color:#F0F0F0
    style BS1 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0
    style BS2 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0
    style BS3 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0
    style BS4 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0
    style BS5 fill:#0A0F1E,stroke:#00C2CB,color:#F0F0F0

1. Physical Risk

Physical risk is the most intuitive channel. Acute events — a Western Cape storm, a KwaZulu-Natal flood like the one that hit Durban in April 2022 — produce immediate insurance claims. Chronic effects — rising sea levels, drought frequency, heat stress — produce gradual shifts in claims frequency and severity that may not trigger a catastrophe model but reshape the expected loss ratio over years.

At the micro channel, physical risk translates directly into underwriting risk: the loss emergence on property, motor, agriculture and business interruption books. It also translates into operational risk when the insurer’s own premises, staff, or key service providers are affected.

At the macro channel, physical risk translates into market risk through asset repricing. A coastal property portfolio held by a listed REIT loses value when flood projections update; the bond issued by that REIT widens; the insurer holding the bond takes a mark-to-market hit. None of this shows up as “climate risk” in the capital calculation. It shows up as spread widening on the asset side and an unexpected correlation between catastrophe losses and asset losses on the same balance sheet event.

2. Transition Risk

Transition risk is what happens when the economy shifts away from the emissions-intensive activities that currently drive underwriting demand and asset values. The policy lever — carbon pricing, emissions caps, disclosure requirements — is usually the proximate trigger. The economic mechanism — stranded assets, sector rotation, technology substitution — is where the balance sheet impact lives.

For motor insurers, the transition to electric vehicles is a live example. EVs change the claims-cost distribution (higher parts cost, different repair supply chain, lower mechanical-failure frequency, distinct thermal-event risk). For a book priced on internal-combustion vehicle data, the pricing assumption becomes wrong as fleet composition shifts. That is transition risk arriving through underwriting risk, via a micro channel.

For life insurers and pension funds, transition risk arrives through the asset portfolio. Equities and bonds in carbon-intensive sectors reprice as investors internalise transition pathways. In South Africa, Sasol and the coal-heavy municipal bond market are the obvious exposures. The macro channel here is sector rotation compounded by liquidity drying up in parts of the fixed-income market — and the insurer’s liability profile determines whether this rotation is tolerable (matched long-dated life book) or painful (short-dated general insurance portfolio).

3. Legal and Reputational Risk

Legal risk is the transmission channel that climate-risk frameworks consistently underweight. The mechanism is not complicated: a party suffers a climate-related loss, identifies a contractual or tortious route to recover from a defendant, and the court agrees. The defendant is often a carbon-intensive company. The insurer is often on the hook via D&O, public liability, or professional indemnity cover.

The reputational channel adds a second loop. An insurer that is publicly tied to underwriting a controversial transition-exposed sector — coal mining, for example, or exploration permits in environmentally sensitive areas — can lose retail and corporate customers independently of any claim or pricing change. This is a channel that affects growth, retention, and eventually the cost of capital.

Both sub-channels hit operational risk and underwriting risk simultaneously, and both are difficult to calibrate because the historical data is sparse. Scenario analysis is the right tool; stress testing on historical losses is not.

Why Channels, Not Drivers

The practical reason to work in channels rather than drivers is that channels map onto capital models. An insurer running a SAM standard formula or internal model already has lines for underwriting risk, market risk, credit risk, operational risk. Climate risk does not need a new capital component. It needs to flow through the existing components via documented transmission assumptions, with the climate driver as the scenario variable that parameterises each channel.

The Prudential Authority’s climate-risk guidance for South African insurers implicitly adopts this framing. So does the Bank of England’s approach, the EIOPA guidance for Solvency II, and the IAIS application paper. The instruction to insurers is consistent: do not calculate a standalone climate capital charge; do demonstrate that climate drivers are reflected in the scenarios and assumptions that feed the existing capital model.

For an actuarial team starting on this work, the first deliverable is a transmission map — a concrete table listing, for each major book and each major asset class, which climate drivers affect it, through which channel, over which horizon, and with what initial assumption for the sensitivity. The map is crude at first. It gets better each cycle. But until it exists, climate-risk reporting is a narrative exercise rather than a quantitative one, and the balance sheet remains exposed to movements the capital model cannot see coming.