“A new study based on 1,000 years of temperature records”
Funny the thermometer wasnt invented until 1592 and it certainly wasnt accurate.
You can get moderately accurate temperature data from (1) tree rings, (2) ice cores, (3) local pollen, and (4) written descriptions of weather events. Cross-referencing these sources produces a statistically reliable estimate, so long as the statistics are done honestly. We know there was far less snow and ice during the Medieval Optimum than there is today. We know the Thames froze annually throughout the Little Ice Age. Both observations are well supported by the reconstructed temperatures from the various proxies for temperature.