Pursuant to yesterday's discussion, particularly for those looking for a bigger picture than just cereal yields. The above shows global production, by weight, of the major food crops. Even by weight, cereals are more than half, and if we were to look at calorie content this would be much more strongly true as fruits and vegetables have a lot of water content.
If we look at the total weight of all these crops, it's been increasing at a very slightly above linear pace:
Thus the picture is the same - global food production is increasing steadily, and the global food supply is becoming more stable. This is not to say there aren't constantly problems with the weather/climate in various places, and many people going hungry. But overall, at the moment, the trend is to greater food production and more stable supply.