Climate change is bad for crop yields. That much has been shown to be true his week. We have had a fantastic summer (now firmly over in this part of the Northern hemisphere). But crop and animal feed yields have been badly affected, not just in the UK but in many parts of the Northern hemisphere. Wheat yields could be well down in both Russia and the Ukraine as well as other places. The situation was complicated since the crop yield could be OK but the protein content affected. Almost every crop in the UK is said to be affected by the hot dry weather and not in positive way.
A number of years ago a right wing American think tank (I believe the American Enterprise Institute) ran an ad campaign along the lines of “they call it pollution we call it fertilizer” stating the scientifically illiterate idea that climate change would increase crop yields due to the increased CO2 levels increasing photosynthesis. Its complicated but this has been found to be untrue. In any case this ignores the other problems to do with climate change. That is the change in weather patterns not just temperatures. When you think about crops have to survive the following wind, sun and rain. The problem with climate change is that the same crops could have excess of the all the above in any one growing season. You can use classical breeding techniques, GM or CRISPAR-CAS9, but engineering resistance to all three will be tricky. So climate change is bad for crop yields. The above idea also ignore the effects of warmer weather on pests and diseases as well. Like many problems related to climate change what we do about this is another matter?