The IPCC’s Sixth Assessment Report highlights the reliance on sustainable socio-economic pathways to meet the 1.5 °C or 2 °C targets. However, these scenarios lack a quantitative assessment of the impact of global military spending on CO2 emissions. Our study shows that events such as the 2001–2011 war on terrorism and the 2022 Russian-Ukrainian war led to an increase in CO2 emission intensity of 0.04 (95% CI: 0.03–0.05) kg/USD for every 1% escalation in global military expenditure as a percentage of GDP (MILEX ratio). This increase accounts for 27% of the total change in CO2 emission intensity between 1995 and 2023. In scenarios where the global MILEX ratio exceeds thresholds of 12% (for SSP1-1.9) or 24% (for SSP1-2.6), the 1.5 °C or 2 °C climate goals would become unattainable by the end of the century, highlighting the urgent need for a more peaceful international environment to effectively limit global warming. Rising global military spending significantly increases CO2 emission intensity, potentially jeopardizing the 1.5 °C and 2 °C climate targets if military expenditure ratio exceeds critical thresholds.