[mrpopo]

This is a reasonable question to ask, although it's also a terribly wrong assumption.

First the ship has already sailed for most of Asia, where the fertility rate is already below 2 or near 2, and the billions extra are just from people getting older. China's population for instance is already expected to decrease from 2030-2035. Asking from these countries to reduce their population is equivalent to asking them to reduce their life expectancy.

In central Africa, the fertility rate is still very high, indeed. But now, remember we are talking about splitting carbon emissions? They already don't emit any carbon. Reducing the fertility rate would still be a good idea, for other reasons (they will be the most impacted by climate change-related disasters for instance).

[melling]

Of course it is the right question to ask.

If 100 million people fly and contribute 2.5% of emissions, and 7 billion people contribute 25% of the omissions are using coal generated electricity, which probably should you solve?

[mrpopo]

1) This is a false dichotomy. We need to reach net zero by 2050 to keep warming below 2 degrees (if we're lucky), therefore we need to solve both.

2) The 100 million people who fly have the most concentrated wealth and therefore have more leeway to implement alternatives to flying (high-speed rail for flights within the US for example).

3) You could also imagine the 100 million people investing to build new low-carbon electricity generation infrastructures in developing countries via a carbon tax on their flight ticket. Of course, they could donate directly as well, either solution is fine. That was actually the spirit of the Paris agreement, which Trump walked out of. Since the 100 million people who fly actively refuse to let go of their wealth, alternative options such as 2) are being considered, even though they might have lower impact (since they affect on the 2.5% of GHG emissions instead of the 25% of GHG emissions).

[melling]

If we had addressed the coal problem 2 decades ago, our net zero goal would have been 2060 or 2070?

Ignoring the coal problem, and actually greatly increasing the coal usage in the past 20 years, has pushed us into a corner where we need miracles. Now "everything" must be addressed!