One at a time. Not 100s within a short time. Krakatoa effected global climate:
Peering through volcanic veils
climate.nasa.gov
One of modern history's largest volcanic eruptions caused tsunamis 3,000 miles away.
qz.com
That is one explosion in the bottom corner of the world.
The US has 1644 deployed warheads,and if you include our ones and the French,probably almost 2000. Russia has 1588:
Russian President Vladimir Putin has announced a deal to deploy tactical nuclear weapons to Belarus.
www.aljazeera.com
3600 between both. A full exchange would be 100s of megatons in a few hours. If you even assume a few 100 that is large quantities of lands irradiated and lots of dust into the air.
People in this thread are watching all the explosions of weapons dumps,etc 100s and 1000s of feet into the air. Make that 100s or 1000s of those at the same time,with 100x or 1000x bigger explosions.
People here are also have this fantasy the russian/american abm systems will shoot down 100% of incoming missiles. If they were 100% reliable,one side would have destroyed the other side by now.
India has more advanced air and missile defences than Pakistan. Will India try and proactively hit Pakistan nuclear sites?
What about North Korea? Why doesn't the US and South Korea strike their nuclear sites first?
Typical internet one-upmanship. I hope for our collective survival we have commonsense people in charge.