In order to avoid certain charge, the analysis involves

New research into global warming published in the journal Science says the northern hemisphere is uniformly warmer now than at any time in the past 1,200 years. It says the present warm period in northern regions is the longest and most widespread temperature anomaly since the 9th century. Researchers have said in the past that the 20th century warming was unprecedented over the past thousand years, at least in the northern hemisphere. But critics disputed the claim, citing periods of extreme warm in certain regions during the Middle Ages. The new study sets out to tackle that criticism head on. Looking at the regional patterns of temperature for the past millennium, it finds while there have been patchy periods of warmth in the past, only in the late 20th century are regions across the hemisphere heating up simultaneously. The analysis is also statistically simpler than previous studies, avoiding the charge that mathematical quirks have generated a false picture of the climate.