Rapid Expansion of Nuclear Arsenals by Pakistan and India Portends Regional and Global Catastrophes

Pakistan’s and India’s rapidly expanding nuclear arsenals may contain 500 weapons with yields between demonstrated values of 12 kt to speculative values of a few hundred kt by 2025. We evaluate one possible scenario for nuclear conflict in 2025 in which India uses 100 strategic weapons to attack urban centers and collocated military targets, and Pakistan uses 150. About 50 million people would die if 15 kt weapons are used, almost 100 million if 50 kt weapons are used, and about 125 million if 100 kt weapons are used. Unfortunately, the consequences for humanity worldwide would greatly exceed these proximate fatalities. Nuclear explosions would start fires in urban areas releasing smoke possibly containing 16 to 36 Tg of black carbon, depending on weapon yields. We use the Community Earth System Model to show that once the smoke rises into the upper troposphere it heats the air by absorbing sunlight, causing the smoke to be self-lofted into the stratosphere where it spreads globally within weeks. Surface sunlight declines by 20-35%, cooling the global surface by 2-5 °C and reducing precipitation by 15-30% for about 4 years, with larger regional impacts. Recovery takes more than 10 years. Agriculture, fisheries and ecosystems would be adversely impacted globally. We predict loss of net primary productivity of 15-30% on land and 5-15% in oceans over 4 years post-conflict, with higher reductions in North America and Eurasia. The consequences depend on how such a war is fought, but can be eliminated if politicians act to reduce this threat to global civilization.