Mass spectrometry and similar analysis methods to look for unexpected proteins in the food parts, followed by feeding the food parts to animals and seeing what happens.
1. Can be solved with phytoplankton, and separately also by more land-area-efficient farming e.g. greenhouses, 2. Can be improved with genetic engineering.
Do the right generic engineering and you even get the oil feedstocks you need for plastics. You could even put the algae in a tube on a rooftop as an alternative to PV, if you could resolve the issue of unwanted other phytoplankton getting in and gumming it up.
A lot of agricultural land is wasted growing crops to feed to animals. If we were to lower meat consumption, agriculture land could be freed for other uses without taking away poor people’s food supply.
If we could convert Sahara back into a savannah or farms, the amount of carbon required for the new soil and plants would exceed the amount of extra carbon we have added to the atmosphere so far. And there are many viable routes to do that. E.g. building large number of ocean thermal energy conversion plants [1] to reduce temperature of the north hemisphere, recreating conditions that have caused green Sahara in the past. There are numerous possibilities to use engineering to revert adverse effects of climate change, and to actually improve the climate. The only scenario when we are doomed, is if population declines significantly so that we get runaway effect from carbon we have already produced melting permafrost, and not have large enough economy to use geoengineering on a large enough scale.
There was a minor problem with stating in air, having plants with large edible parts, talking with people far away. Science and engineering have helped with all these minor problems, and they can help with the new one if we spend money on geoengineering research instead of wasting it on inefficient "clean energy".
Does this include ocean farming based carbon capture? That sounded like a pretty positive route in terms of land use limitations when I heard about it.