fix(ciceroscmpy2): hold aerosols at PI for idealised conc-driven runs#108
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benmsanderson merged 2 commits intoJun 25, 2026
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On the concentration-driven path (abrupt-4xCO2, 1pctCO2) _build_scendata_list sets emstart=nyend so CO2 stays concentration-driven. That also gated the user-supplied emissions overlay in _build_hybrid_emissions_data at `year >= nyend`, so the PI-flat aerosol / ozone-precursor emissions were applied only at the final year and every prior year fell back to the rising historical_em baseline. The result is a spurious growing aerosol cooling that drifts ERF down ~0.6 W/m2 across a 4xCO2 step (GSAT peaks ~1950 then cools) instead of holding flat. Decouple the overlay-application year from the model emstart via a new overlay_from argument, and pass nystart for idealised runs so the supplied PI emissions apply across the whole window. CO2 is unaffected: it is not supplied on the conc-driven path and stays concentration-driven via conc_run. The emis-driven esm-flat10 family already used emstart=1850 and is unchanged. Verified on abrupt-4xCO2: ERF now flat to +/-0.000 W/m2 (was -0.64) and GSAT rises monotonically with no spurious mid-run cooling. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
benmsanderson
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openscm:feat/fair2-ciceroscmpy2-adapters-and-runmode-nonfork
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Problem
On the concentration-driven idealised path (
abrupt-4xCO2,1pctCO2),_build_scendata_listsetsemstart = nyendso CO2 stays concentration-driven.But that value also gated the user-supplied emissions overlay in
_build_hybrid_emissions_dataatyear >= emstart— so the PI-flat aerosol /ozone-precursor emissions a caller supplies were applied only at the final
year, and every prior year fell back to the rising
historical_embaseline.The effect is a spurious growing aerosol cooling: ERF drifts down ~0.6 W/m²
across a 4×CO2 step (so GSAT peaks ~1950 then cools) instead of holding flat.
The emissions-driven
esm-flat10family was unaffected because it usesemstart = 1850.Fix
Decouple the overlay-application year from the model
emstartvia a newoverlay_fromargument to_build_hybrid_emissions_data, and passnystartfor idealised runs (
natural_off and lu_zero) so the supplied PI emissionsapply across the whole window. CO2 is unaffected — it is not supplied on the
conc-driven path and stays concentration-driven via
conc_run.Verification
abrupt-4xCO2, CICEROSCMPY2, 10 members: ensemble-median ERF now flat to±0.000 W/m² (was −0.64 W/m² 1850→2000), and GSAT rises monotonically toward
equilibrium with no mid-run cooling.
Surfaced during AR7 WG1 Ch5 idealised-experiment QA.
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