Global Warming Amplifies the Risk of Uncertainties in Projections of Deepened Summer Thaw Depth Across Northern Hemisphere Zone

Abstract

A warming climate endangered to destabilize the expansive permafrost zone and its summer thaw depth in the northern part of the earth. This climatic shift exacerbated the challenges associated with predicting future summer thaw depths, thereby escalating the associated risks. To examine the influence of uncertainties in future global warming on these predictions, we conducted 2,829 numerical simulations across 21,786 grids at a 0.5° resolution within the Northern Hemisphere using a land model that accurately described the physical processes of freezing and thawing. To mitigate the impact of errors in model physical parameters on the uncertainty of estimated summer thaw depths, we proposed a standardized orthogonal bounded parameter perturbation (SOBPP) method. This approach was implemented to build an ensemble prediction system (EPS) based on the advanced Lund-Potsdam-Jena Wetland Hydrology and Methane (LPJ-WHyMe) model, called as LPJ-WHyMe-OPEPS. LPJ-WHyMe-OPEPS was evaluated for its ability to simulate summer thaw depths using 264 observational data across various fields. The results demonstrated that LPJ-WHyMe-OPEPS outperformed simulations without the EPS in simulating summer thaw depths. Under global warming scenarios, uncertainties extents in projections of summer thaw depth within the northern permafrost zone increased over time when using LPJ-WHyMe-OPEPS. Additional numerical experiments revealed that the magnitude of uncertainty growth in summer thaw depth predictions due to climate warming surpassed that in the absence of climate warming. These findings underscored the escalating challenges in predicting the dynamics of the northern summer permafrost zone in response to ongoing global warming.