More than a couple years at most

a–f, Changes in surface temperature (a), solar radiation © and precipitation (e) averaged over global crop regions of 2000 (Supplementary Fig. 1) and sea surface temperature (b), solar radiation (d) and net primary productivity (f) over the oceans following the six stratospheric soot-loading scenarios studied here for 15 years following a nuclear war, derived from simulations in ref. 18. These variables are the direct climate forcing for the crop and fishery models. The left y axes are the anomalies of monthly climate variables from simulated nuclear war minus the climatology of the control simulation, which is the average of 45 years of simulation. The right y axes are the percentage change relative to the control simulation. The wars take place on 15 May of Year 1, and the year labels are on 1 January of each year. For comparison, during the last Ice Age 20,000 years ago, global average surface temperatures were about 5 °C cooler than present. Ocean temperatures decline less than for crops because of the ocean’s large heat capacity. Ocean solar radiation loss is less than for crops because most ocean is in the Southern Hemisphere, where slightly less smoke is present.

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