 Out of the blue in 1998 Britain s leading science journal Nature long supportive of the warming orthodoxy published a new paper on global temperature changes over the previous 600 years back to 1400 Its chief author was Michael Mann a young physicist turned climate scientist at the University of Massachusetts who had only completed his PhD two years before In 1999 he and his colleagues published a further paper based only on North America but extending their original findings over 1000 years 