Solar activity cycles (1868–2022) and global GDP with a lag of 2 years (1870–2024): R2=1.0 (SA growth phase, 58 years of observations) and R2=0.9971 (SA decline phase, 111 years of observations)

Subject of the study: This paper examines the causal relationship between solar activity cycles (1868-2022) and global GDP growth rates for the period 1870-2024, i.e., with a lag of two years. Methodology: The author develops the methodological approach of W.S. Jevons and A.L. Chizhevsky, supplementing it with the modern biochemical concept of Russell Reiter. Key results: 1. Statistical reliability: A very high correlation was found between the indicators: the determination coefficient was 0.95 for all twelve years of the average solar activity cycle over 155 years of observations. 2. Three-zone biochemical model: The mechanism by which ultraviolet (UV) radiation influences the economy through human neurochemistry is substantiated: - "Biological depression" zone (Wolf number (W) < 20): UV deficiency leads to decreased serotonin levels, creating pessimism and stagnation in global GDP with a 2-year lag. - "Biological optimum" zone (W = 20 - 140): Sufficient levels of serotonin and melatonin ensure optimism and peak global GDP growth rates with a 2-year lag. - "Biological stress" zone (W > 140): Extreme solar activity suppresses melatonin production (according to R. Reiter's concept), causing "exhaustion pessimism" and a sharp decline in global GDP growth with a 2-year lag. Forecast: Based on the model, the expected global GDP growth rates are calculated: 2.91% in 2025, 2.4% in 2026, and 3.3% in 2027. A significant slowdown in growth to 2.4% is predicted in 2032 due to reaching the solar minimum in 2030.