A nuclear leakage or tactical nuclear weapon use in a limited war could cause immense and long-lasting ecological consequences beyond the direct site of exposure. We call upon all scientists to communicate the importance of the environmental impacts of such an event to all life forms on Earth, including humankind. Changes to ecosystem structure and functioning and species extinctions would alter the biosphere for an unknown time frame. Radiation could trigger cascade effects in marine, atmospheric and terrestrial ecosystems of a magnitude far beyond human capabilities for mitigation or adaptation. Even a “tactical nuclear war” could alter planet Earth’s living boundaries, ending the current Anthropocene era.