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2026
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| Online Access: | https://doi.org/10.5281/zenodo.19635955 |
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| _version_ | 1866902071466262528 |
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| author | Mayer, Jörg |
| author_facet | Mayer, Jörg |
| contents | <p><strong>Paper 8 of the forest-climate series, version 3.</strong></p><p>Paper 8 v3 documents the same forest-water mechanism across two latitude regimes — tropical (Amazon) and mid-latitude (Central Europe) — as different phases of a single tipping trajectory. Key findings:</p><ul><li><strong>NH/SH natural experiment (ERA5, 1979–2024):</strong> Northern Hemisphere extratropical warming +1.318 °C vs. Southern Hemisphere +0.398 °C (3.31× ratio). Symmetric CO₂ forcing explains at most ~30 % (±5–8 %) via the Southern-Hemisphere baseline; the remaining ~70 % is NH-specific.</li><li><strong>Amazon-STJ causal chain (proven mechanism, PCMCI+, 425 monthly data points 1985–2024):</strong> Amazon bio-AOD → Atlantic STJ (β = +0.142, p = 0.005, τ = 3 months) → Atlantic sea ice (β = +0.150, p = 0.003, τ = 1 month). Bidirectionally coupled: NH warming → Amazon bio-AOD (β = +0.182, p < 0.001, τ = 1 month).</li><li><strong>Central European ET-tipping (currently dominant magnitude):</strong> Three-region OLS attribution (Amazon, Iberia, Central Europe) combined with a 75-year ERA5 reconstruction shows the evapotranspiration-temperature coefficient has inverted to +2.80 over Central Europe (vs. −1.64 over Amazon). JJA r(slhf, t2m) reversed sign around 2005 — the empirical fingerprint of water-limited evapotranspiration. Contribution: ~57 % of the 2003–2024 NH-SH divergence increment.</li><li><strong>Amazon channel decomposition:</strong> Direct ET −6.1 %, aerosol-CCN +3.7 %, STJ-sea-ice teleconnection +18.3 % → net ~16 % of the 2003–2024 increment.</li><li><strong>Framework limitation as finding:</strong> Baron-Kenny mediation with 5 mediators fails bootstrap for all; same data yield p < 0.005 under PCMCI+. Single-mediator linear attribution is structurally unsuitable for bidirectionally coupled systems (Runge et al. 2019).</li><li><strong>Multi-region tipping-phase heterogeneity:</strong> CALIPSO vertical profiles (2007–2019) place four mid-latitude forest systems (Iberia, SE Pine, Appalachians, Pacific NW) in an Amazon-parallel descending-convection phase. Pan-Arctic warm-band broadening +9–11° latitude across all three gateways confirms regime change is not Atlantic-specific.</li></ul><p>The policy consequence: European groundwater restoration is the currently dominant actionable lever for NH warming mitigation, alongside ongoing tropical-forest protection. Retained v1/v2 retraction banners within the PDF.</p> |
| format | Recurso digital |
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| institution | Zenodo |
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| publishDate | 2026 |
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| spellingShingle | Forest Loss and Northern Hemisphere Warming Asymmetry: Causal Evidence from a Bidirectionally Coupled System Mayer, Jörg Northern Hemisphere warming asymmetry subtropical jet stream Arctic amplification deforestation evapotranspiration tipping Central Europe groundwater PCMCI+ causal discovery bidirectional coupling NH/SH natural experiment three-region attribution ERA5 ERA5-Land CALIPSO Amazon biogenic aerosol climate tipping points <p><strong>Paper 8 of the forest-climate series, version 3.</strong></p><p>Paper 8 v3 documents the same forest-water mechanism across two latitude regimes — tropical (Amazon) and mid-latitude (Central Europe) — as different phases of a single tipping trajectory. Key findings:</p><ul><li><strong>NH/SH natural experiment (ERA5, 1979–2024):</strong> Northern Hemisphere extratropical warming +1.318 °C vs. Southern Hemisphere +0.398 °C (3.31× ratio). Symmetric CO₂ forcing explains at most ~30 % (±5–8 %) via the Southern-Hemisphere baseline; the remaining ~70 % is NH-specific.</li><li><strong>Amazon-STJ causal chain (proven mechanism, PCMCI+, 425 monthly data points 1985–2024):</strong> Amazon bio-AOD → Atlantic STJ (β = +0.142, p = 0.005, τ = 3 months) → Atlantic sea ice (β = +0.150, p = 0.003, τ = 1 month). Bidirectionally coupled: NH warming → Amazon bio-AOD (β = +0.182, p < 0.001, τ = 1 month).</li><li><strong>Central European ET-tipping (currently dominant magnitude):</strong> Three-region OLS attribution (Amazon, Iberia, Central Europe) combined with a 75-year ERA5 reconstruction shows the evapotranspiration-temperature coefficient has inverted to +2.80 over Central Europe (vs. −1.64 over Amazon). JJA r(slhf, t2m) reversed sign around 2005 — the empirical fingerprint of water-limited evapotranspiration. Contribution: ~57 % of the 2003–2024 NH-SH divergence increment.</li><li><strong>Amazon channel decomposition:</strong> Direct ET −6.1 %, aerosol-CCN +3.7 %, STJ-sea-ice teleconnection +18.3 % → net ~16 % of the 2003–2024 increment.</li><li><strong>Framework limitation as finding:</strong> Baron-Kenny mediation with 5 mediators fails bootstrap for all; same data yield p < 0.005 under PCMCI+. Single-mediator linear attribution is structurally unsuitable for bidirectionally coupled systems (Runge et al. 2019).</li><li><strong>Multi-region tipping-phase heterogeneity:</strong> CALIPSO vertical profiles (2007–2019) place four mid-latitude forest systems (Iberia, SE Pine, Appalachians, Pacific NW) in an Amazon-parallel descending-convection phase. Pan-Arctic warm-band broadening +9–11° latitude across all three gateways confirms regime change is not Atlantic-specific.</li></ul><p>The policy consequence: European groundwater restoration is the currently dominant actionable lever for NH warming mitigation, alongside ongoing tropical-forest protection. Retained v1/v2 retraction banners within the PDF.</p> |
| title | Forest Loss and Northern Hemisphere Warming Asymmetry: Causal Evidence from a Bidirectionally Coupled System |
| topic | Northern Hemisphere warming asymmetry subtropical jet stream Arctic amplification deforestation evapotranspiration tipping Central Europe groundwater PCMCI+ causal discovery bidirectional coupling NH/SH natural experiment three-region attribution ERA5 ERA5-Land CALIPSO Amazon biogenic aerosol climate tipping points |
| url | https://doi.org/10.5281/zenodo.19635955 |