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Highly energetic events, such as asteroid or comet impacts, regional explosive volcanism, and combined nuclear explosions, are now recognized as capable of ejecting sufficient material into the air to induce large variations in transmitted sunlight and cause global perturbations in the Earth's atmosphere. Depending on seasonal timing, pronounced changes in the global atmospheric temperature to colder, hotter, or rapid cycling could greatly stress the biosphere, including the forest ecosystems. For example, if global temperatures rapidly dropped 10°C during late spring in the Northern Temperature Zone, we predict from new cold-hardiness studies that on the order of 50 percent of the forests in these latitudes could be killed within a few days. We further estimate that the forests killed under these conditions would have a minimum total wet biomass of about 0.5 × 1012 m3. After drying, the dead forest will have a biomass equal to about 0.2 × 1012 t. Wildfires initiated by lightning strikes would burn this dry biomass and should be significantly larger and more numerous than in normal years. The total amount of fuel consumed from all sources would vary globally depending on the weather, but we estimate that the atmospheric soot produced by wildfire burning of just the forest biomass killed in the Northern Temperate Zone could reach and probably exceed 108 t over a short time. In addition, we infer that such a complex environment could cause cyclic periods of both dark/cold and light/hot conditions in the atmosphere.

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