Although global nuclear arsenals have shrunk since the Cold War, global society continues to face the risk of a global or regional nuclear warfare with emerging nuclear states and rising geopolitical tension. In a hypothetical nuclear war scenario, along with the extreme local destruction, firestorms that are triggered at targeted urban centers are capable of injecting aerosols into the upper troposphere – lower stratosphere. The aerosols, which are comprised of black carbon (BC), can be transported and spread globally. BC is a highly absorbing aerosol. Using global climate models, previous studies have shown that the BC can absorb incoming solar radiation, locally heat the upper atmosphere, and cause prolonged surface cooling for years. Consequently, shortage in global food supply, famine, and further conflicts may be caused. However, considerable uncertainties remain in the estimated amount of injected BC and in the climate response. In this study, CanESM has been used to study the climate response to a nuclear war scenario for the first time. The results will be shown for a scenario that corresponds to a lower estimated amount of injected BC. The transport of BC as well as the surface impacts will be discussed. A robust and long-term global surface cooling is found, consistent with the literature. A rapid short-term surface warming is also found in the first year of the simulations, following the very initial cooling.