Because observed regime trends substantially exceed the forced LENS2 range for key regimes despite matching ensemble-mean signs, internal variability likely dominates the observed regime changes while a weak forced dynamical signal may be emerging.

Because observed regime trends substantially exceed the forced LENS2 range for key regimes despite matching ensemble-mean signs, internal variability likely dominates the observed regime changes while a weak forced dynamical signal may be emerging.

• The forced LENS2 ensemble mean has the same sign as all observed weather-regime trends, but the observed WR2 and WR3 trends lie entirely outside the ensemble range, and only 7 of 100 members have a more negative WR1 trend than observed.
  Evidence for this premise (4)

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Weather-regime changes as mechanisms of circulation-driven drying

  the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends.

  https://doi.org/10.1038/s41561-026-02050-w#unit-4-p3

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Weather-regime changes as mechanisms of circulation-driven drying

  the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends.

  https://doi.org/10.1038/s41561-026-02050-w#unit-4-p3

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Weather-regime changes as mechanisms of circulation-driven drying

  The ensemble mean trend agrees in sign with all observed WR trends; however, only 7 out of 100 members exhibit a stronger negative WR1 trend than observed, and the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends. This suggests that internal variability, rather than the forced response alone, plays a likely dominant role in driving the observed WR trends over the analysis period.

  https://doi.org/10.1038/s41561-026-02050-w#unit-4-p3

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Weather-regime changes as mechanisms of circulation-driven drying

  The ensemble mean trend agrees in sign with all observed WR trends; however, only 7 out of 100 members exhibit a stronger negative WR1 trend than observed, and the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends. This suggests that internal variability, rather than the forced response alone, plays a likely dominant role in driving the observed WR trends over the analysis period.

  https://doi.org/10.1038/s41561-026-02050-w#unit-4-p3
• CESM2 forced circulation trends are much weaker than the observed trends in every identified weather regime, implying that internal variability likely dominates.
  Evidence for this premise (2)

  European summer drying largely driven by atmospheric circulation changes since the 1980s

  Forced circulation trends in CESM2 are much weaker than the observed trends in each identified weather regime … which implies internal variability as a likely dominant contributor

  https://doi.org/10.1038/s41561-026-02050-w#unit-6-p4

  European summer drying largely driven by atmospheric circulation changes since the 1980s

  Forced circulation trends in CESM2 are much weaker than the observed trends in each identified weather regime … which implies internal variability as a likely dominant contributor

  https://doi.org/10.1038/s41561-026-02050-w#unit-6-p4
• Although the LENS2 ensemble-mean weather-regime trend has the same sign as every observed trend, only 7 of 100 members have a more negative WR1 trend than observed, and observed WR2 and WR3 trends lie wholly outside the LENS2 range.
  Evidence for this premise (4)

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Partitioning post-1980 hydroclimate trends between circulation and thermodynamic forcing

  the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends

  https://doi.org/10.1038/s41561-026-02050-w#unit-3-p10

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Partitioning post-1980 hydroclimate trends between circulation and thermodynamic forcing

  the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends

  https://doi.org/10.1038/s41561-026-02050-w#unit-3-p10

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Partitioning post-1980 hydroclimate trends between circulation and thermodynamic forcing

  The ensemble mean trend agrees in sign with all observed WR trends; however, only 7 out of 100 members exhibit a stronger negative WR1 trend than observed, and the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends.

  https://doi.org/10.1038/s41561-026-02050-w#unit-3-p10

  European summer drying largely driven by atmospheric circulation changes since the 1980s — Partitioning post-1980 hydroclimate trends between circulation and thermodynamic forcing

  The ensemble mean trend agrees in sign with all observed WR trends; however, only 7 out of 100 members exhibit a stronger negative WR1 trend than observed, and the observed WR2 and WR3 trends fall entirely outside the range of LENS2 trends.

  https://doi.org/10.1038/s41561-026-02050-w#unit-3-p10

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