So the authors are expecting higher prices for products based on grain.
What I worry about it the wealthy countries command so much more wealth that the increased costs wouldn't be enough for us to reduce our consumption of grain. For me the difference between a pound of wheat for 70 cents and 1.70 isn't all that significant, but for global poor living on less than $2/day that's a gigantic change.
Reducing our grain consumption in America can be done easily by simply eating less meat. For example according to Eating to save the Earth if just America reduced its meat consumption by 10 percent the grain saved would be sufficient to feed 60 million people.