http://mwplisbon2010.fc.ul.pt/pdf/Abstracts.pdf

Evidence from 180 proxy records of widespread Northern Hemisphere warmth in the 9th to 11th centuries

Fredrik Charpentier Ljungqvist (1), Paul J. Krusic (2), Anders Moberg (2), Hanna S. Sundqvist (2), and Håkan Grudd (2)

(1) Department of History, Stockholm University; (2) Department of Physical Geography and Quaternary Geology, Stockholm University

We find evidence of a widespread medieval warming culminating in the 10–11th centuries, followed by a gradual cooling into the 17th century, succeeded by a dramatic warming from the 18th century that accelerated into the 20th century. Our result also indicates that the warmth in the 10th and 11th centuries was as uniform as is the current 20th century warming.

h/t to Marc Morano