Scenario Analysis vs Stress Test: Two Tools, One Climate Question

In climate-risk submissions I’ve reviewed, scenario analysis and stress testing are often presented as interchangeable labels for the same exercise. They are not. They are two distinct tools that answer two different questions, produce two different sets of outputs, and serve two different regulatory purposes. Treating them as synonyms is one of the most common mistakes in climate-risk reporting, and it shows up as soon as a reviewer asks which decision the output was meant to inform.

Scenario analysis is exploratory. It asks: under a defined future pathway, how does the insurer’s position evolve? It produces a narrative plus quantitative outputs across multiple time steps, showing how losses, assets, and capital ratios develop along the pathway. The horizon is long, the number of scenarios is modest, and the point of the exercise is strategic — to identify which pathways the insurer is robust under and which it is not.

Stress testing is a point-in-time integrity check. It asks: if this shock hits the balance sheet today, can the insurer still meet its obligations? It produces a single post-stress position for capital ratios, liquidity coverage, and solvency. The horizon is short, the shock is severe, and the point of the exercise is regulatory and prudential — to prove resilience at a defined confidence level.

The Two Tools Side by Side

Dimension	Scenario Analysis	Stress Test
Core question	How does the insurer evolve under this pathway?	Can the insurer survive this shock?
Horizon	10–30 years (NGFS: 30)	Instantaneous or 1 year
Path dependence	Yes — outputs depend on the full trajectory	No — single-period shock
Number of paths	Usually 2–4 contrasting pathways	Usually 1 severe case, sometimes with reverse stress
Output shape	Time series of KPIs and balance-sheet items	Post-shock balance sheet and solvency ratios
Primary regulatory use	IFRS S2, ORSA forward-looking view, strategic planning	SAM/Solvency II capital adequacy, PA returns
Typical question it answers	Where should we be underweight by 2040?	Have we capitalised the tail today?

The overlap is real. Both exercises use severe-but-plausible future conditions. Both require an economic scenario, a mapping to the insurer’s exposures, and a re-valuation of assets and liabilities. Both should inform management action. But the outputs are not substitutable — and a submission that presents a single catastrophe-loss shock as a “climate scenario analysis” is not meeting the requirement.

A Worked Mini-Example

Consider a short-term insurer with a Western Cape property book, exposed to a combination of fire, flood, and storm peril. Two climate-linked exercises on the same book:

Scenario analysis (NGFS-aligned, 1.5°C disorderly transition, 30-year horizon). The scenario parameterises an emissions pathway, a physical-hazard trajectory, and a macroeconomic response. The insurer projects, across 30 annual time steps, the expected loss ratio on the property book, the market value of the asset portfolio, and the resulting capital ratio. The output is a chart showing capital ratio by year under the pathway, compared to baseline. The strategic finding: the book is tolerable until year 12, after which rising physical losses compound with transition-driven asset-price declines, and the capital buffer erodes.

Stress test (2% P&L shock on the same book). The scenario is a single-period catastrophe event: a 1-in-200-year storm producing a gross loss equivalent to 2% of pre-stress surplus. The insurer calculates the post-loss SCR coverage ratio. The output is a single number: SCR coverage after the event. The prudential finding: the book is capitalised against the defined stress, with the SCR ratio remaining above the supervisory threshold.

These two findings are not redundant. The scenario analysis tells the insurer where to reposition over time. The stress test tells the insurer whether it survives the next twelve months. Neither one on its own is sufficient for an ORSA submission that claims to address climate risk.

Where Each Tool Belongs

For ORSA purposes, the Prudential Authority’s guidance — and the IAA’s practice guidance on climate-risk ORSA — is explicit that both tools have a role. Scenario analysis covers the forward-looking, strategic dimension: does the business model remain viable under defined pathways? Stress testing covers the point-in-time resilience dimension: is the current capital sufficient for defined adverse events? An ORSA that presents only one of the two leaves a known gap.

For IFRS S2 disclosure, scenario analysis is the primary tool. The standard requires disclosure of the resilience of the insurer’s strategy to climate-related risks and opportunities, assessed through scenario analysis. Stress-test outputs can appear as supporting metrics but do not substitute for the scenario work.

For internal capital-model work under SAM, stress testing and reverse stress testing are the immediate tools; climate-aware scenario analysis increasingly feeds the calibration of the market-risk and catastrophe-risk modules.

The Trap to Avoid

The trap is presenting a climate-coloured catastrophe loss estimate as a scenario analysis. A single 1-in-100-year Cape Storm modelled with 2050 hazard parameters is a stress test with a climate-adjusted input. It is useful. It is not scenario analysis. It does not tell you whether the book is viable under a 1.5°C disorderly transition pathway; it tells you whether the book survives one hypothetical event under a plausible future hazard.

The reverse trap is presenting a 30-year scenario output as evidence of current solvency. The capital ratio in year 15 of a 2°C pathway is informative for strategic planning. It is not a statement about whether the balance sheet is adequate today.

Both tools are necessary. They are not interchangeable. A climate-risk programme that invests in one without the other is going to miss either a strategic risk that compounds over years, or a prudential risk that crystallises in a single event. The insurers I’ve seen handle this well treat the two tools as complements: the scenario analysis sets the long-run direction of travel, and the stress test checks that the next quarter is survivable while the strategy plays out.