Tree ring data reconstructs the local effects of global warming on maize farming in the 1200s.

During the Medieval Warm Period of the 1200s, around 40,000 people moved north in Colorado due to drought leaving them unable to grow their crops. The temperature change was around 1 ^oC (much smaller than the temperature change we are seeing now), but the localized change in precipitation had a significant effect on the Pueblo culture.

The study of localized regions in assessing the effects of climate change is therefore extremely important in determining what type of environments will be most effected by climate change. The study in Nature Communications has used two different types of tree rings to reconstruct the temperature and rain profile across Southwest America for the past 2000 years. The shift in precipitation and temperature patterns allowed the regions where maize, the staple crop of the 1200s (and today), to be identified and this temperature change caused a mass migration North.

Large climate differences in such a small geographical area suggest that some regions will be hit harder than others during global warming. Although the full impact of this temperature fluctuation is small, it is clear that the Southwest went through a major change at this time.

Humans will have to adapt to the larger and more rapid climate change occurring today. In the past our ancestors clung on to their farming techniques by moving region, but there will be less suffering if humans are able to develop and employ alternative strategies. The implications of this study are that detailed local studies to identify present and future farming environments are key in assessing resources and their distribution change during climate change.

http://www.nature.com/ncomms/2014/141204/ncomms6618/full/ncomms6618.html