I will start off with stating that I could have just misunderstood the reading and podcast. According the the article, the plague was known to start out in rats, but they believe there was another way it came back since the plague would kill off many species. They thought it was possibly the climate that brought it back, but didn't have enough evidence to prove it. In the podcast, Monica Green talks about how the disease was transferred through grain. Could grain be how the climate is connected?
Grain grows in the ground, so whatever is in the air and soil will be incorporated into the grain. (Keepin mind I have no science background so I could be so far-off.) could the plague have been in the ground, but managed to reach the grain over many years of evolution, allowing it to spread again?