James Haywood, University of Exeter & Hadley Centre, Exeter, UK

Model studies suggest that intense fires subsequent to the detonation of nuclear warheads would create so-called ‘nuclear-winters’ that could persist for many years leading to global famine. Even regional-scale wars could pose an existential threat to ecosystems and humanity. Here, we utilise a fully-coupled version of the UKESM1 Earth System model to assess the impacts of three different nuclear scenarios i) all-out USA-Russia nuclear war, ii) war between India-Pakistan, iii) more limited nuclear conflicts in eastern Europe. Different numbers of nuclear detonations, vertical profiles, and seasons of conflict are assumed over each area and the climate response is analysed over the subsequent twenty year period. For USA-Russia and India-Pakistan nuclear scenarios, the results are compared to those from significantly less sophisticated and significantly coarser resolution models to examine the fidelity of the earlier results. The new scenarios examine the climatic impacts of the detonation of as few as ten Hiroshima sized nuclear warheads over eastern Europe. Analyses include the physical evolution and longevity of the stratospheric plume and the response in terms of near-surface temperatures, precipitation, stratospheric ozone, induced changes in atmospheric and ocean dynamics, impacts on net primary productivity, ecosystem adaptability and impacts on crop productivity.