Update CHANGELOG

Author: znichollscr

changelog/413.breaking.md

@@ -1 +1,26 @@
-Added data with the source ID `FZJ-CMIP-ozone-2-0` and recommended that the historical data from `FZJ-CMIP-ozone-1-2` not be used for historical simulations
+Added data with the source ID `FZJ-CMIP-ozone-2-0`.
+This data updates the historical forcing data provided in `FZJ-CMIP-ozone-1-2`.
+
+As a result of an issue being found ([#400](https://github.com/PCMDI/input4MIPs_CVs/issues/400)),
+models that rely on exogenous ozone forcing are now required to use different versions of the ozone files
+for pre-industrial control (and related) simulations and historical (and related) simulations.
+For all historical (and related) simulations, files with the source ID `FZJ-CMIP-ozone-2-0` should be used.
+For pre-industrial control (and related) simulations, files with the source ID `FZJ-CMIP-ozone-1-2` should be used
+(note that this guidance differs from the email communication sent by the CMIP IPO on 12 February 2026).
+For details of your options for pre-industrial control simulations,
+please see [the ozone dataset page](https://input4mips-cvs.readthedocs.io/en/latest/dataset-overviews/ozone/).
+
+The CMIP Panel co-chairs are recommending that,
+for modelling centres who rely on ozone as an external forcing,
+historical, and other relevant DECK (e.g., AMIP), simulations
+should be re-run with the `FZJ-CMIP-ozone-2-0` ozone if possible.
+(Pre-industrial control simulations do not need to be re-run
+because they are unaffected by the release of `FZJ-CMIP-ozone-2-0`.)
+
+If any modelling centres cannot re-run their historical simulations,
+they should contact the ozone forcing providers for guidance on
+how to ensure a smooth connection between the scenario ozone forcing files.
+
+If any modelling centres run historical simulations
+with both the `FZJ-CMIP-ozone-1-2` and `FZJ-CMIP-ozone-2-0` forcing,
+these simulations would be of interest to the Forcings Task Team.