It depends on climate more than shifting crops from animal feed to human food. Plants evolved over millions of years under specific conditions that all are synergistic. Air and soil temperatures, hours of daylight, which are different in the spring than they are in the summer regardless of temperatures (and dark for some plants), moisture that is both atmospheric (humidity) and ground (root feeding), levels of light intensity (is it April or July light intensity), all affect the ability of plants to grow, flower, pollinate, and produce seeds (grains, the foundation of civilization). The ability to produce seed is also their ability to reproduce new plants for new crops.

People are saying that if food supplies begin to fail, we can just stop feeding the cows. Only if the reason the food supplies begin to fail is NOT because of climate problems, water problems, excess heat problems, and the rest of the conditions that all plants need. The plants we eat and the plants we feed the cows and the chickens all require the same stable growing conditions.

The biggest danger we face in connection with food sources is the reliability of stable climate, and there are a few big threats. They include extreme heat, and that can be extreme heat only for a very short duration during the time that plants produce pollen. Even if your growing season is conducive to plants doing well throughout more than 90% of the year, if there is a rise in temperatures during a short period of two weeks at the wrong time, you won't get any seeds that year. That one is scary, because it doesn't require a sustained increase in temperatures, only one of short duration. We've already seen it cause crop failure in some places, including the US.

Short-term extreme heat affects other food sources, like seafood. The heat dome of 2021 killed a billion sea animals off the coast of British Columbia, so such an effect isn't limited to plants alone. Fish stocks are also declining rapidly, even without extreme heat. Salmon fish stocks in the Pacific northwest that have existed for four to five million years are disappearing even in Alaska, which little more than a decade ago was still considered a very viable fishery region. Ocean acidification and warming are affecting food supplies and reproduction cycles.

Another serious problem is the loss of insect pollinators. Another is the failure of things like the AMOC, which could produce extreme heat in some places while producing extreme unseasonal cooling in others. We saw that last year with wavering air currents that are stablized by the differential between warm air and cold air in the northern hemisphere. The far north Pacific northwest had an extreme warm winter, even in coastal northern Canada and Alaska, almost no snow cover and relatively few days that were even below freezing. The northern midwest, however, was clobbered with extreme cold for months.

We really should never have screwed with things we don't understand so much, but the hubris of our culture won't allow us to understand how much we don't understand. We hear too much about "man's ingenuity," which consists primarily of rearranging things we cannot make, and too little about biology.