Threshold effects of CO₂ on Sea-Ice Volume:Empirical Evidence with Data from Global Circulation Models of the Arctic and Antarctic

Alvaro Escribano and Juan Andrés Rodríguez

UC3M Working papers. Economics from Universidad Carlos III de Madrid. Departamento de Economía

Abstract: The year 2024 marked a critical milestone in global warming, with global mean temperatures exceeding pre-industrial levels by 1.55 °C. Polar ice loss, largely driven by anthropogenic CO₂ emissions, exhibits highly nonlinear dynamics that challenge conventional linear modeling approaches. This paper investigates the nonlinear effects of CO₂ on Arctic and Antarctic sea-ice volumes using regime-switching econometric models defined for both accumulated concentration levels and annual changes in CO₂. Specifically, we estimate reduced-form Smooth Transition Autoregressive (STAR) and Threshold Autoregressive (TAR) specifications using data generated from General Circulation Models (GCMs). We consider the identification of CO₂ thresholds and the evaluation of sea-ice dynamics under alternative CO₂ emissions trajectories, such as the IPCC’s Shared Socioeconomic Pathways (SSPs). Our results reveal important threshold effects across hemispheres. For the Arctic, a single CO₂ threshold is identified at approximately 330 ppm (or 𝛥𝐶𝑂2 = 1.16 ppm), while for the Antarctic, two thresholds emerge at 285 ppm (or 𝛥𝐶𝑂2 = 0.13 ppm) and 321 ppm (or 𝛥𝐶𝑂2 = 0.56). Beyond these points, the decline in sea-ice volume accelerates sharply. Forecasts under business-asusual (BAU) scenarios suggest that the Arctic could become ice-free around 2060 [2045, 2078], while Antarctic sea-ice loss may extend well beyond 2100. Under an intermediate emissions path, such as SSP2-4.5, recovery of sea-ice volume remains feasible if global CO₂ growth begins to decline after 2035 by an average of 3.2 ppm every year, with projected reversion to historical levels around 2075 for both hemispheres.

Keywords: Climate; change; Climate; econometrics; Sea-ice; volume; Shared; socioeconomic; pathways; (SSPs); Smooth; transition; autoregressive; (STAR); models; Threshold; autoregressive; (TAR); models; CO₂; concentration; thresholds (search for similar items in EconPapers)
JEL-codes: C32 C38 C5 C51 C52 (search for similar items in EconPapers)
Date: 2025-11-18
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