It's been my experience, as a farmer mind you not a climate scientist, that land becomes infertile mostly because of how it's farmed. Most of my organic farmer friends have land that is becoming more fertile overtime as they implement restorative farming practices.
Obviously climate change is altering our weather in ways that will require changes in our practices and I'm in a part of the world where those alterations are unlikely to make farming impossible. There are, none the less, a group of farmers engaged in dry farm trials here - in preparation for more limited irrigation water.
The declining levels of nutrients in food often has to do with the process of selection and breeding as well as farming techniques. Many older varieties, and some newer ones bred for better nutrition, have much higher levels of nutrients than those available in your average grocery store. Farmers like me are growing, selecting and then propagating fruit and vegetable varieties that are both more resilient to climate instability and more nutritious. In contrast to generations of ag research that bred for productivity, storage and transport without even noticing that nutrition had diminished.
Some of the most exciting research related to nutrient levels in vegetables and fruits is finding that stressful environments with insect pests, periods of drought and fungal attacks produce food with markedly higher nutrients than those farms awash in abundant chemical fertilizers and irrigation. Ted Radovich in Hawaii has done some interesting research in this.
Apples, a specialty of mine, have markedly more nutrition in areas of the fruit with scab on the surface. Truly, our most nutritious apples are in the cider bin.
I do think it's a dangerous idea that we can kill the planet and still feed ourselves and dangerous to let those leading the earths destruction spread that idea. I'd certainly rather have science and technology help us restore our ecosystems than prepare us to live in some blade runner post apocalyptic nightmare. I also concur with Neven that we can't mimic soil. Soil scientists will tell you that there are billions of microbes in a handful of soil and we understand maybe 10% of them. There is an entire other world under our feet and we are only beginning to explore it.