Soil Organic Carbon shock (SSP3-7.0)

Source: IPCC CMIP6 (cSoil ensemble) Year: 2050 Category: Scenario Coverage: Global Format: Raster grid Used in risk analysis: No (contextual layer; not used in materiality scoring)

What it shows

This layer is a forward-looking scenario variant showing the projected change in soil organic carbon under the SSP3-7.0 pathway — a high-emissions, regional-rivalry development scenario. Soil organic carbon underpins soil fertility, water retention and carbon storage, so projected losses signal places where soil condition and the natural services it supports may be eroded most severely under a high-warming future.

Note on the scenario. This is the pessimistic pathway used across Darwin's stress test. It is SSP3-7.0, which replaced the previous SSP5-8.5 layer — the IPCC AR6 treats SSP5-8.5 as physically implausible, so SSP3-7.0 is now the high-end reference.

How it is built

This is a scenario projection rather than a present-day observation. Values represent the projected relative change in soil carbon content, expressed as a percentage shift relative to a baseline. The SSP3-7.0 pathway represents a high-emissions "regional rivalry" future and therefore typically the most severe end of the projected range. The result is delivered as a global grid showing the modelled change in soil carbon stocks.

How to read it

Values express how much soil carbon is projected to gain or lose relative to today under this scenario. More negative values indicate larger projected losses of soil carbon — a greater shock to soil condition — while values near zero or positive indicate stability or gain. Because this is the high-emissions pathway, projected shocks are generally larger than under the sustainable SSP1-2.6 variant, making it useful as a worst-case stress test.

Class thresholds

The underlying quantity is a physical flux expressed as a relative change: the projected percentage change in soil organic carbon (SOC) stocks under the SSP3-7.0 pathway, relative to a present-day baseline (% change). The surface is symbolised as a continuous diverging gradient rather than discrete risk classes, anchored on the SOC shock (%) field over the domain −35 % to +35 %:

The layer carries a single hazard trigger: a high SOC-shock zone is defined where the projected change falls below −30 % (i.e. more than 30 % of soil carbon is projected to be lost). This layer is a contextual scenario variant and is not used in materiality scoring, so that −30 % value acts as a flagging threshold for display rather than a live risk gate.

How these thresholds were set. The continuous SOC-change quantity is taken from the underlying soil-carbon scenario projection (formal source attribution pending). The diverging colour breaks (−35 / −10 / 0 / +10 / +35) and the −30 % high-shock cut-off are a Darwin in-house classification — symmetric round-number percentage bins around zero, not derived from a published external standard.

Source

Projected relative change in soil organic carbon under the SSP3-7.0 (regional-rivalry, high-emissions) scenario, expressed relative to a baseline. (Formal source attribution pending.)

Comparison with the WWF Risk Filter Suite

The WWF Risk Filter Suite publishes present-day indicators only and does not include forward-looking soil-carbon scenario projections, so this layer has no direct equivalent. It is a temporal/scenario variant of the underlying soil-condition theme that WWF covers (Biodiversity Risk Filter S2_1 Soil Condition) for the present day, extended here to a future high-emissions pathway.

Legend

Symbolised field: SOC shock (%)

Generated from darwin/layers/layer-soc-shock-ssp5.toml and risk_indicator_pairs.toml (develop).