Seeming as though almost every first world country is below their replacement rate, and even emerging countries (India, Nigeria, DRC) are achieving peak population much earlier than expected, I believe we'll have a global population crisis in the next 10-20 years.
It'll be an unprecedented trend that no one really knows how it will play out exactly, but there are a few ideas:
* First world countries will lean heavily on immigration to sustain the workforce (we're seeing this now), until the pipeline dries up
* Programs like Social Security and Medicare will cease to exist in their current forms since there will be more people drawing from it than paying in
* The housing market will flip upside down, there will be more houses than people so entire markets will crash and probably never recover, the hardest hit being the suburbs. Cities should still be okay.
* Global GDP will tank, so stock markets may start declining or going sideways due to smaller workforce/less innovation. Deflation is a definite possibility
* AI/Robotics will probably be a huge player in some form, maybe quantum computing finally?
Obviously it's impossible to tell the future, especially decades in advance. However, I'm sure there are some things you can invest in now that will pay off when you're close to retirement age, when you'll need it most. What are your thoughts?