Fig. 1: The relationship between global military expenditure ratio and global CO2 emission intensity.
a Time series of detrended global CO2 emission per unit of GDP (emission intensity; kg/USD in constant 2017 of purchasing power parity; represented by the blue line), global military expenditure as a percentage of GDP (MILEX ratio; pink line), and three-year weighted average global MILEX ratio (red line) from 1995 to 2023. The global MILEX ratios for 1995 and 1996 are not weighted. The study period is divided into four phases, showcasing a relatively peaceful phase (highlighted with a light-green background) and a phase of frequent regional wars (marked with a light-orange background). The boxes below display the major events or wars of each phase. b Scatter plot of the weighted MILEX ratio and detrended CO2 emission intensity from 1995 to 2023, along with the fitted line (black line) for the two variables with a slope of 0.04 (95% confidence interval: 0.03–0.05).
