Someone in reddit (http://www.reddit.com/r/askscience/comments/reo35/the_discus...) pointed to an article noting that a 7 degree warming would suck moisture from the ground and substantially inhibit plant/food growth.
From http://www.nasa.gov/topics/earth/features/climate_by_any_oth...
>> But temperature change itself isn't the most severe effect of changing climate. Changes to precipitation patterns and sea level are likely to have much greater human impact than the higher temperatures alone. For this reason, scientific research on climate change encompasses far more than surface temperature change. So "global climate change" is the more scientifically accurate term. Like the Intergovernmental Panel on Climate Change, we've chosen to emphasize global climate change on this website, and not global warming.
Edit: and of course a bunch of other times during the Phanerozoic - I just picked one.