Either we come up with green energy replacements for both transportation/ag energy and electricity that don't cost a lot more than current energy sources do, or we lose technological civilization, in which case I'd regard 1M as optimistic.

If there are 9.2 billion people on this planet in 2050, and we haven't switched over completely to an entirely carbon-free energy source, then we will have irreversibly changed the Earth's climate for the next 3000 years.  Nobody right now knows what that climate will look like, or whether the planet will still be habitable.

Given that fact, XOVER may be an optimist.

I personally would argue that, in the face of climate change, questions of food and water become meaningless.  You can fill the planet with mana from heaven, but if the Earth of 2050 isn't habitable, it doesn't matter.