A Post-1998 Transition from Water-Vapor to Joint Greenhouse Gas Forcing regime over Nigeria

Abstract. Anthro-forced climatic oscillations across the West African sub-region present severe challenges to regional ecological resilience, yet the fine-scale causal interactions governing localized thermal feedback loops remain elusive. This study bypasses traditional linear constraints by deploying a novel multivariate causality block network tracking architecture to evaluate multi-decadal surface air temperature (SAT) fluctuations across Nigeria. Utilizing a spatially continuous 44-year atmospheric profile from the NASA MERRA-2 reanalysis platform (1981–2024), this paper maps the evolving coupling between thermodynamic states and localized trace gas mixtures. The causality tracking identifies a profound, systemic regime shift structurally anchored to the historic 1998 climate tipping point. This transition is marked by a sharp SAT anomaly step-change, climbing from a pre-1998 baseline of −0.64 °C to a post-1998 mean of 0.16 °C, coupled with a 66 % expansion in internal thermal variance. While individual trace gas metrics yield weak standalone diagnostic correlations, masking their true impact, non-parametric distributional tracking confirms deep structural divergence across the two temporal eras (p < 0.001). Crucially, the multivariate network analysis uncovers a fundamental atmospheric paradigm shift: Nigeria's historical thermal baseline, once regulated by natural water-vapor feedbacks, has transitioned into a highly sensitive, multi-driver configuration. Forecast error variance decomposition demonstrates that contemporary Nigerian SAT shifts are now explicitly driven by a synergistic combination of internal chaotic atmospheric dynamics and joint greenhouse gas forcing. These findings uncover a localized thermodynamic vulnerability, providing an empirical basis for further investigation into the underlying climate mechanisms, spatial heterogeneity, and subcontinental patterns of climate sensitivity and adaptation.