According to a post on Celsias, rice yields drop 10% for every degree of warming (celsius or fahrenheith isn't specified). The article continues, "it’s not just temperature overall, it’s actually the warmer night time temperatures that has the adverse effect. At the same time, population increases require a 1% annual increase in rice production to keep up with demand."
So much for that longer growing season for one of the staple crops of a very large portion of the worlds population. Some countries are taking steps to prevent unrest over rising costs and reduced availability by banning or reducing exports. Read more about it at "Fears of Unrest as Rice Prices Surge 30%."