It's an interesting bar bet for armchair historians: Name the worst year in human history. For Harvard medieval historian Michael McCormack, the smart money is on 536. "It was the beginning of one of the worst periods to be alive, if not the worst year," he tells Science. Start with the then-mysterious fog that descended over Europe, the Middle East, and Asia—and stayed for 18 months. Not only was it dark and freezing pretty much all the time, the resulting crop failure led to mass starvation. A team led by McCormick and a glaciologist now think the fog can be blamed on the eruption of a volcano in Iceland, one that blew again in 540 and 547. The fog helped give the decade following 536 the unwanted distinction of being the coldest in 2,300 years, but it was only part of the era's misery.
Bubonic plague came along in 541, and this "black death" took a devastating toll on a populace already decimated by starvation. As news.com.au notes, all of this was taking place a mere 60 years or so after the collapse of Western Roman Empire. Roads and bridges were crumbling, and violent "local strongmen" filled the leadership void. So when did things finally start turning around? McCormack suggests an answer for that as well: Figure around 640. In a study in Antiquity, his team reports a spike in particulate lead in layers of ice from that time. The appearance of the lead suggests the global economy was on the mend: It came from silver mining needed to produce coins, say the researchers. (Read more discoveries stories.)