One way of understanding how climate change is likely to affect global food production and food security is to better understand the recent past. That is, how have changes already influenced agricultural activities and production? For example, considerable debate has taken place on whether
future impacts in agriculture will be driven mainly by rising temperatures, or if instead precipitation changes are the main concern. The answer to this would influence strategies to adapt, such as investing in heat tolerance versus waiting for better rainfall projections.

http://iis-db.stanford.edu/pubs/23212/policy_brief_trends11.pdf