Global crop failures is pretty far fetched. Even the IPCC lowers the projections every year. Not a denier in the least, but we have over-estimated the impact in a huge way.
Im sure it wont be like a biblical plague, but the IPCC report that came out moments ago reiterated the 20 year to 1.5 C+ timeline. What matters is if a crop failure hits a nation with few friends and lots of nukes.