i at least know what the word "marginal" means, which your comment makes clear you do not. reducing population to 1 billion in foreseeable future can only be achieved through genocidal means, it is an absurdist suggestion.
I have several decades in exploration geophysics, in my actual experience "forseeable future" has a long timescale, something your comment makes clear you do not think in.
"Reducing population" is phrased as an active control of population numbers. Populations fluctuate by other means than just genocidal ones, and I made no mention of one billion as a taget.
have a good one