New to Worldbuilding

Hi, I have recently had ideas for a post environmental apocalypse world set in our world during the 21st century. The idea is that following a major world war the world's nations turned their focus to space exploration. The new increase in rocket launches and space travel caused a rapid increase in climate change. This rapid change in climate and its effects on the world caused the collapse of all major organised governments. That is a brief summary of my idea and if anyone has any other suggestions they would be very welcome as Im brand new to this. Im also not sure what part of the world to focus on, Im from the UK but my inspirations such as Fallout and The Walking Dead are focused in the US. Also does anyone have any advice on storing this information or even what to use it for? Thanks in advance