Climate Change Medieval Style

"Between around 950 and 1250 global temperatures in the Northern Hemisphere rose, and although this rise was by no means evenly felt across the globe, it provided the longest sustained period of benign climate conditions in the west since the Roman Climate Optimum. Although, as we shall see, the so-called Medieval Warm Period would not last throughout the Middle Ages, it made conditions in Europe relatively favorable to agriculture. The natural advantage coincided with the development of new horse harnesses and large iron plows ("heavy" plows) that allowed massively more efficient large-scale agriculture. And as this technologies combined with the effects of fluctuating climate, landholding became ever-more profitable and landowners had ever more income to spend."  

From Dan Jones Powers and Thrones. Many echoes from that period and today.