1860's and later - Slightly Cooler Climate

My curiosity is peaked by the possible effects of a slightly cooler global climate on world history from the just before the American Civil War era...and later. Perhaps an average of 2 or degrees cooler globally, but otherwise parallel to the general temperature increases and decreases as in OTL. There could be more difficult winters, some more crop failures, and even the bubonic plague popping up a little more in some places. Droughts due to slightly less precipitation.

I suppose it would give Russia an advantage in WW-2.
 
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