Population decline is very well documented. The global trends hide countries like Germany, South Korea, and Japan where the numbers have sunk as low as 1.3 births / female, far below replacement.

The world might have more people by 2100 but many countries, including US, Europe and others will be shrinking, unless they take aggressive action on immigration reform.

My personal belief is this is ultimately how humans will go extinct. Not with a bang (apocalyptic global warming, war, famine, etc) but a whimper (gradual fade out into black over the next 1000 years).