The reality is that we are discussing are two unpalatable possibilities.
The first choice is to radically reduce our quality of life and hugely curtail our consumer tendencies and thus our individual environmental impact.
The second choice is to curtail the human population and get it back down to a level where the global economy is sustainable whilst having a very modest environmental footprint, whilst allowing individuals to enjoy a reasonable standard of living.
The problem is that neither of these is realistic and in fact, I don't think the bulk of the countries in the world today actually have large enough populations to get their economies to grow to the point they reach a level of prosperity whereby population growth is seen as being undesirable.
The human population on Earth will hit 10 billion I think before the world's poorest reach a level of prosperity whereby they don't need to have children merely to survive.
One of the biggest obstacles to economic development is access to reliable and affordable energy, principally that means electricity.
And today, for the much same reasons no one on this thread has yet told me what the alternative is to the UK consuming 60 million tonnes of crude oil a year, the means the poorest economies in the world are going to pursue coal as an energy source for at least the next 30 years if not longer. We're talking 600+ million people in the world today with absolutely no electricity whatsoever, and probably around 3 billion people (depending on whose estimates you use) who can't yet obtain a level of energy consumption roughly equal to that which an average household in the developed world would consume without blinking: about 2000 kilowatt hours give or take.
The answer is to make the lower 50% of the human race wealthier. You do this with trade and by spreading prosperity and wealth. You enable stable government with realistic regulation and careful law making. You provide access to reliable, affordable energy and secure supplies of water, food and sanitation, along with basic healthcare.
What you do not do, is exploit other countries for their natural resources or worse, hoover up the youngest, most mobile and most productive members of their societies by enabling vast amounts of migration. That is both exploitative and a criminal waste of precious human resource.
And so now in this single post we have come nearly full circle and begun to illustrate just how complex an issue carbon emissions actually are and that there is no short or quick or simple answer because there are a huge number of moving parts to this problem. You can't hugely tax air travel in the name of saving those Islands in the Seychelles, because those same Islands rely heavily on income from tourism to sustain their way of life. Cutting off that income stream would be as damaging to them as a rise in sea levels.