Question: what is nuclear winter?

Philip Dolan answered on 13 Jun 2011:

I’m not an expert in this, but a nuclear winter is a predicted climatic effect should large numbers of nuclear weapons be detonated. I think it was a bigger worry back in the cold war (when the USA and USSR were making large numbers of nuclear weapons). The idea is that when you make lots of these kinds of explosions, loads of ash and dust and debris get shot up really high in the atmosphere. This then stops a lot of the sunlight getting down to the surface (for a long time, like 3 or 4 years), as it takes a long long time to settle. This makes the surface much colder, and could possibly trigger ice ages.

Interestingly it is thought that the exact same thing killed off the dinosaurs, except rather than nuclear weapons it was caused by a big meteor hitting the earth (or possibly a massive volcanic eruption). Either way the same thing happens, that the sunlight gets blocked and the surface temperature plummets, and in this case all the cold blooded lizards (i.e. the dinosaurs) couldn’t bask in the sun to warm themselves up, and were supplanted by us warm blooded mammals, that generate all our body heat from our food and don’t really need so much sunlight.

Sorry it’s a bit of a long answer!