Let me reiterate here that Liam Dodd is not an expert in this period of history. He's a very good Physicist, but his expertise is largely due to information that I fed him about the conditions, plus some statistics that he was able to dig up.
It's a great overview, but he's careful to tell me that we have to dig deeper for the most up to date and precisely informed thinking in the field. Academics. Always covering their backs.
(And for the record, I trust his opinion on this stuff.)
From about 1250, and throughout the rest of the 13th and 14th centuries, temperatures began to drop. Glaciers crept forward and heavy rain destroyed crops throughout Northern Europe, America and Asia. Thousands died in famines, especially between 1315-17. So what had Physics done to us, Liam?
"The reason that it rained a lot is that the cold front was screwed up, due to the encroaching glaciers. This caused the climate cycle to be off. As the cold front advanced, there was much more stormy weather. It was hitting the warm front in places where it hadn't before."
By the 15th century, the weather was swinging through extremes. One year would see everyone shivering in the cold all year round, buffeted by terrible storms and unseasonal snow. The following year would be a heatwave.
Liam had a stark warning, even more unsettling than those weather conditions. "What happened then is what is going to happen to us soon." Undeterred by my alarm, he plunged on. "The shifting weather systems caused large variables. The whole weather system was being knocked out of play."
"So it was like a pendulum?" I asked. "The weather swinging around trying to find something it liked?"
"No. One variable would cause the next." Liam informed me, in a tone of voice which discouraged thinking of the weather as something sentient. "It was a positive feedback loop, whereby each climatic event would push the next even further out of whack. The weather patterns kept changing, because that cold front was colliding with the warm front ever further south."