The problem is one that future generations of people are living 'better' lives, so can afford more meat, can afford air travel, can afford to buy something like a smart phone.
20 years ago, the idea of a smart phone was very uncommon, now most people consider them an essential item. It doesn't really matter how much effort we put on to the material engineering, the fact is it's a new category of environmentally unfriendly things, one that everyone wants, and probably only for a few months before replacing too.
So whilst we can try and be more efficient in these matters, It's obvious that a decline in population is going to be the fastest. This is before we get on to those pesky places that have recently massively improved their quality of life, such as China or most of SEA.