How Extreme Space Weather Impact Earth’s Atmosphere and Climate: Exploring N₂O and the Faint Young Sun Paradox

Space weather (SWE) strongly influences Earth’s atmospheric chemistry and climate. The young Sun, far more magnetically active than today, produced frequent and intense solar energetic particle (SEP) events that continuously bombarded Earth’s upper atmosphere. These high‑energy particles triggered chemical pathways capable of generating greenhouse gases such as CO, H₂, N₂O, and HCN [1–4].Using a three‑model framework—a thermochemical–photochemical kinetics model [5,6], a radiative–convective model (EOS) [7], and an energy balance model (ESTM) [8,9]—we investigated how an extreme SWE event alters atmospheric composition and affects climate. Our goal was to test whether SEP‑driven chemistry could contribute to resolving the Faint Young Sun Paradox (FYSP), as suggested by Airapetian et al. [1].SEP‑induced dissociation of N₂ produces N(²D), initiating chemical pathways that form N₂O, HCN, H₂, and CO. For Archean‑like atmospheres (90% N₂, 10% CO₂, with trace CH₄ or H₂), CO and H₂ are the dominant products, but the resulting surface warming does not exceed 0.3 K—insufficient to address the FYSP. Nitrogen‑bearing species contribute negligibly. Even enhancing SEP fluxes by an order of magnitude leaves atmospheric composition and climate response largely unchanged. Under modern atmospheric conditions, repeated Carrington‑like SEP events would instead cool Earth’s surface by ~4 K. These results indicate that although extreme space weather significantly alters atmospheric chemistry, its climatic impact remains too small to resolve the FYSP.This work has recently been published in The Astrophysical Journal (ApJ) as Biasiotti et al. (2026), ApJ, 996, 93 [10].References [1] Airapetian, V. S., Glocer, A., Gronoff, G., Hébrard, E., & Danchi, W. (2016). Nature Geoscience, 9, 452. [2] Solomon, S., Roble, R. G., & Crutzen, P. J. (1982). J. Geophys. Res., 87, 7206. [3] Solomon, S., Reid, G. C., Rusch, D. W., & Thomas, R. J. (1983). Geophys. Res. Lett., 10, 257. [4] Jackman, C. H., & McPeters, R. D. (2004). In Solar Variability and its Effects on Climate, Geophysical Monograph 141, 305. [5] Locci, D. et al. (2022). Planetary Science Journal, 3, 1. [6] Locci, D. et al. (2024). Planetary Science Journal, 5, 58. [7] Simonetti, P. et al. (2022). ApJ, 925, 105. [8] Vladilo, G. et al. (2015). ApJ, 804, 50. [9] Biasiotti, L. et al. (2022). MNRAS, 514, 5105–5125. [10] Biasiotti, L. et al. (2026). ApJ, 996, 93.