Amid the "pick your apocalypse" options the world faces right now - climate change and nuclear annihilation loom pretty high.
Just two weeks ago the Bulletin of Atomic Scientists moved the Doomsday Clock forward by a second, to make it 89 seconds to midnight.
Someone who knows an awful lot about what a catastrophic nuclear conflict would result in is Alan Robock, one of the world's leading experts on the climatic effects of a nuclear conflict.
He's also an expert in geoengineering - that's a broad term for interventions to combat the effects of climate change - and something he's expressed concerns about.
He's in New Zealand and giving a talk tonight at Victoria University of Wellington on the human toll of nuclear winter.
