It's during the cooling periods (i.e. the Little Ice Age from around 1300 to 1850, or Dark Ages from 300 to 900 AD) that plagues increase (along with other calamities like crop yields going down and rain patterns harder to predict). But during warming periods plagues go down. I know it's hard to see that with last year and the Spanish Flu after WW1, but we have less plagues during the Current Warming Trend (since around 1850) and during the Medieval Warm Period (900 to 1300) and Roman Warm Period (the time of Christ) than during the cooling periods.
By the way, the calamities of the Little Ice Age was a factor, not the only one, of most of the historical atrocities we're supposed to forever be angry about. Things like western expansion into the America's, the demand for slaves, the African leaders capturing and selling slaves when crop yields went down (not enough crops to export, but they had too many people to feed), and intertribal wars in the Americas. I'm not saying there weren't other motivations (i.e. some intertribal wars were revenge wars). I'm just saying when crop yields go down you're motivated to have war for crop land (instead of war for oil). When you have to feed and clothe tons of people back home you need a ton of labor to work that land to squeeze out what you can from it (demand for slaves). When the land you live in gets too cold you take over land south of you (like an Iroquis splinter tribe did when it kept taking over land from other tribes further and further south until it settled in modern day Georgia and Alabama -- we call them the Cherokee).
I'm not justifying all of these events. I'm just saying the same left that wants us to be obsessed with past atrocities is somehow also the ones that don't want us to celebrate that we keep moving away from the recent cooling period that motivated a lot of the atrocities.
Just about ten thousand years ago, or so, there was no such thing as the great lakes.
Cant let the truth get in the way though. Around 535 AD one of the largest volcanic eruptions in history happened and that kicked in a major disruption in earths climate.