PM2.5 shock (SSP1-2.6)

Source: IPCC CMIP6 (GFDL-ESM4, GISS-E2-1-G, MIROC-ES2L) Year: 2050 Category: Scenario Coverage: Global Format: Raster grid (~100 km) Used in risk analysis: No (contextual layer; not used in materiality scoring)

What it shows

This layer measures the projected change in fine particulate matter (PM2.5) air pollution between today and mid-century under a sustainable-development future. Rather than showing the absolute level of pollution, it highlights where air quality is expected to deteriorate or improve the most, so users can see where future change — not just present conditions — drives air-pollution risk.

How it is built

The shock is derived from CMIP6 climate-model projections under SSP1-2.6, an optimistic low-emissions pathway. For each location it compares projected 2050 PM2.5 against a 2014 baseline and expresses the difference as a relative change. The change is then dampened in already very clean areas: where baseline concentrations sit below a health-relevant "very low" threshold, the signal is attenuated so that ultra-clean regions such as the Arctic and open ocean do not show misleadingly large percentage shocks. The result is a coarse global grid (roughly 100 km cells).

How to read it

Higher positive values mean a larger projected worsening of fine-particulate pollution by 2050; values near zero mean little expected change; negative values indicate projected improvement. Because clean baseline regions are deliberately down-weighted, the most prominent signals appear in already-populated or already-polluted areas.

Class thresholds

The underlying quantity is a physical flux expressed as a relative change: the projected percentage change in fine-particulate (PM2.5) air pollution between a 2014 baseline and a 2050 projection, under the SSP1-2.6 pathway (% change). It is computed as (PM2.5_2050 − PM2.5_2014) / (PM2.5_2014 + 1st_decile) × weight, where weight = min(1, PM2.5_2014 / 5.8×10⁻⁹ kg/kg) attenuates the signal in ultra-clean regions (concentrations below the health-relevant "very low" threshold of 5.8×10⁻⁹ kg/kg).

This layer is not split into discrete risk classes. It is symbolised on the PM2.5 purity shock (%) field as a continuous diverging gradient over its native unit, the shock percentage:

The layer is contextual and is not used in materiality scoring, so it carries no five-class risk table. It does, however, define a single trigger: a location is marked as a High PM2.5 shock zone when the projected degradation exceeds 30 % (purity shock below −30 %), which feeds the Enabling/Supporting Services dimension.

How these thresholds were set. This is a Darwin in-house classification: the PM2.5 concentrations come from the CMIP6 multi-model ensemble (GFDL-ESM4, GISS-E2-1-G, MIROC-ES2L) under SSP1-2.6, but the shock formula, the 5.8×10⁻⁹ kg/kg attenuation threshold, the ±90 % gradient anchors and the −30 % High-shock trigger are fixed round-number cutoffs chosen by Darwin's scenario pipeline, not a published CMIP6 or WWF class break.

Reference: CMIP6 (WCRP Coupled Model Intercomparison Project Phase 6) — wcrp-climate.org/wgcm-cmip/wgcm-cmip6.

Source

CMIP6 climate models (WGCM CMIP6 ensemble), models GFDL-ESM4, GISS-E2-1-G and MIROC-ES2L, scenario SSP1-2.6; 2014 baseline versus 2050 projection.

Comparison with the WWF Risk Filter Suite

The WWF Risk Filter Suite publishes present-day risk indicators, not forward-looking scenario shocks. This layer is a temporal change-variant of an air-quality risk WWF only assesses for current conditions, so it has no distinct WWF equivalent and is a Darwin scenario extension.

Legend

Symbolised field: PM2.5 purity shock (%)

Generated from darwin/layers/layer-pm25-shock-ssp1.toml and risk_indicator_pairs.toml (develop).