Impacts of Nuclear War on Terrestrial Carbon Processes

A simulated nuclear war between the United States and Russia, resulting in an injection of 150 Tg of black carbon into the upper troposphere and lower stratosphere, would have significant impacts on climate. We used the Whole Atmosphere Community Climate Model version 4 coupled with the Community Land Model version 4 with a fully interactive carbon-nitrogen cycle to simulate this nuclear conflict and offline Community Land Model version 5 to further study the impact of nuclear war on terrestrial carbon processes. In the first five years following the conflict, global average land temperature decreases by 15 ^oC, precipitation decreases by 50%, and shortwave radiation declines by 60%. These sudden changes in the physical climate system induce large perturbations to the terrestrial biosphere. We observe a global-average reduction in gross primary production (GPP) of 60%, with 100% reductions over mid- and high-latitude regions. Plants respond differently to nuclear war depending on their location and type. The reduction in GPP is primarily driven by temperature reductions in the extra-tropics, and by the reduced solar radiation in the tropics. We also observe reductions in autotrophic and heterotrophic respiration, driven by reductions in temperature, precipitation, and radiation. The reduction of GPP is much stronger than autotrophic respiration, and therefore net primary production under nuclear winter significantly decreases. Together with soil respiration, the global terrestrial biosphere releases 6.5 Pg C yr^-1 more in the first 5 years following the conflict than in the current climate.