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2026
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| Online Access: | https://doi.org/10.5281/zenodo.19593523 |
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| _version_ | 1866902071323656192 |
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| author | Mayer, Jörg |
| author_facet | Mayer, Jörg |
| contents | <p><strong>⚠️ THIS VERSION (v1) IS SUPERSEDED BY v2. Please cite the concept DOI 10.5281/zenodo.19593522 which always resolves to the latest version.</strong></p><p><strong>Reason for supersession:</strong> The Baron–Kenny mediation analysis claiming "42.4% of NH warming via STJ–sea-ice cascade" did not survive bootstrap robustness testing (pair bootstrap, block bootstrap, parametric Monte Carlo; all 95% CIs include zero). v2 removes this claim, adds pan-Arctic gateway analysis, documents bidirectional coupling limits, and reframes around PCMCI+ as the primary attribution tool.</p> <p><strong>Paper 8 of the forest-climate series.</strong></p><p>We present three lines of evidence that tropical forest loss — not greenhouse gas forcing — is the primary driver of Northern Hemisphere (NH) warming asymmetry. Using ERA5 reanalysis (1979–2024) and a NH/SH natural experiment, we find that CO₂ explains at most 30.2% of NH extratropical warming (+1.318°C vs. SH +0.398°C). The NH subtropical jet stream (STJ) has weakened significantly (−0.237 m/s/decade, p=0.045, N=46), while the SH shows no trend (p=0.766). Baron–Kenny mediation confirms 77.5% of this STJ weakening propagates to NH excess warming via Arctic sea ice loss (R=−0.863, p<0.001). Monthly PCMCI+ causal discovery (N=425 months, 1985–2024) resolves the full deforestation cascade: Amazon bio-AOD → Atlantic STJ (β=+0.142, p=0.005, τ=3 mo) → sea ice (β=+0.150, p=0.003, τ=1 mo), with total lag ≈11 months. A positive feedback loop is also confirmed: NH warming → Amazon bio-AOD (β=+0.182, p<0.001, τ=1 mo). Aerosol sensitivity analysis using IPCC AR6 best-estimate forcing shows that even under maximum aerosol-unmasking assumptions, at least 30–40% of NH warming requires NH-specific forest–STJ mechanisms. The detected feedback loop implies potential irreversibility of the deforestation-driven warming cascade.</p> |
| format | Recurso digital |
| id | zenodo_https___doi_org_10_5281_zenodo_19593523 |
| institution | Zenodo |
| language | |
| publishDate | 2026 |
| publisher | Zenodo |
| record_format | zenodo |
| spellingShingle | Forest Loss as the Primary Driver of Northern Hemisphere Warming Asymmetry: A PCMCI+ Causal Attribution Study of the Subtropical Jet–Arctic Cascade Mayer, Jörg Northern Hemisphere warming asymmetry subtropical jet stream STJ Arctic amplification deforestation PCMCI+ causal attribution NH/SH natural experiment sea ice Hadley circulation Amazon biogenic aerosol Baron-Kenny mediation ERA5 MERRA-2 tropical forests climate tipping points <p><strong>⚠️ THIS VERSION (v1) IS SUPERSEDED BY v2. Please cite the concept DOI 10.5281/zenodo.19593522 which always resolves to the latest version.</strong></p><p><strong>Reason for supersession:</strong> The Baron–Kenny mediation analysis claiming "42.4% of NH warming via STJ–sea-ice cascade" did not survive bootstrap robustness testing (pair bootstrap, block bootstrap, parametric Monte Carlo; all 95% CIs include zero). v2 removes this claim, adds pan-Arctic gateway analysis, documents bidirectional coupling limits, and reframes around PCMCI+ as the primary attribution tool.</p> <p><strong>Paper 8 of the forest-climate series.</strong></p><p>We present three lines of evidence that tropical forest loss — not greenhouse gas forcing — is the primary driver of Northern Hemisphere (NH) warming asymmetry. Using ERA5 reanalysis (1979–2024) and a NH/SH natural experiment, we find that CO₂ explains at most 30.2% of NH extratropical warming (+1.318°C vs. SH +0.398°C). The NH subtropical jet stream (STJ) has weakened significantly (−0.237 m/s/decade, p=0.045, N=46), while the SH shows no trend (p=0.766). Baron–Kenny mediation confirms 77.5% of this STJ weakening propagates to NH excess warming via Arctic sea ice loss (R=−0.863, p<0.001). Monthly PCMCI+ causal discovery (N=425 months, 1985–2024) resolves the full deforestation cascade: Amazon bio-AOD → Atlantic STJ (β=+0.142, p=0.005, τ=3 mo) → sea ice (β=+0.150, p=0.003, τ=1 mo), with total lag ≈11 months. A positive feedback loop is also confirmed: NH warming → Amazon bio-AOD (β=+0.182, p<0.001, τ=1 mo). Aerosol sensitivity analysis using IPCC AR6 best-estimate forcing shows that even under maximum aerosol-unmasking assumptions, at least 30–40% of NH warming requires NH-specific forest–STJ mechanisms. The detected feedback loop implies potential irreversibility of the deforestation-driven warming cascade.</p> |
| title | Forest Loss as the Primary Driver of Northern Hemisphere Warming Asymmetry: A PCMCI+ Causal Attribution Study of the Subtropical Jet–Arctic Cascade |
| topic | Northern Hemisphere warming asymmetry subtropical jet stream STJ Arctic amplification deforestation PCMCI+ causal attribution NH/SH natural experiment sea ice Hadley circulation Amazon biogenic aerosol Baron-Kenny mediation ERA5 MERRA-2 tropical forests climate tipping points |
| url | https://doi.org/10.5281/zenodo.19593523 |