SEDAC is relatively optimistic about crop yields under climate change

That's Socioeconomic Data and Applications Center at Columbia University.

They are optimistic--very optimistic--relative to our predictions, at least for corn and soybeans in the United States.  Our predictions are based on statistical analysis; theirs are based on yield simulation models.

They have also analyzed the whole world and have a cool interactive web page where you can see maps of their predictions.

Here's their map for corn.