by Gabi Hegerl
Over the coverage of 'climategate' and on lots of blogsites the view persists that Mike Mann's hockeystick is the one and only scientific obstactle to a warm (ie as warm as the late 20th century or warmer) medieval warm period.
Actually, there are scores of reconstructions of climate in the Northern Hemisphere over the last millennium, and none that I am aware of has the medieval warm period warmer than the late 20th century. Yet there are also lots of publications of individual records that show that the medieval warm period was very warm in places. This is no contradiction: the unusual thing about the recent warming is its widespread nature. While the medieval warm period was warm in places, it wasn't warm everywhere on the Northern Hemisphere, and it wasn't warm in different places at the same time. As the readers who are interested in climate point out, climate varies a lot. It is warm one place at one time and cold at another place at the same time (because the atmosphere shifts conditions around while it varies its circulation naturally, and the ocean does similar things). What the climate system cant usually do without external influences is create sustained, longterm and widespread warming trends - for that, you usually need external influences on climate.
So don't blame the hockeystick for getting rid of a warmer-than-today medieval warm period - climate science did that.