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The decade ending in 2006 was the warmest such period in the Northern Hemisphere for at least the last 1,300 years and possibly longer, says a new study written by a University of Arizona researcher and six other researchers.

The study, slated for publication next week, is the latest of three reports by some of these researchers contrasting recent temperatures with those of hundreds or more years ago.

Because this study used a broader array of research data, the scholars say they have more confidence in their findings than in the earlier studies. Those studies, involving what was called a “hockey stick” diagram showing a dramatic rise in recent temperatures, brought them worldwide scientific fame and recognition by an international climate change panel that studies global warming. But they also sparked controversy and a congressional investigation.

The new study concluded that the average Northern Hemisphere temperature over that recent decade was at least a bit more than half a degree Fahrenheit warmer than the historical, decade-long averages dating back 1,300 to 1,700 years. More likely, they were close to a full degree warmer than historical averages, the study found.

The paper is “one brick in the wall” of the case for saying that human-induced causes such as greenhouse gas emissions are raising temperatures, said Malcolm Hughes, a dendrochronologist at UA’s Laboratory of Tree-Ring Research.

Other pieces of evidence are more important, including the atmosphere’s basic physics and what is already known about the amounts of gases such as carbon dioxide, methane and nitrous oxide that humans have been putting into the atmosphere, Hughes said.

“It is not the foundation stone. We are not claiming that,” Hughes said of the latest study’s contribution to theories of human-caused global warming. “We are part of the supporting cast of this case. The results that we have are consistent with what we know about how climate is controlled, as consistent as they can be given the uncertainties.”

But this study also offers much more reliable conclusions than the earlier studies, because they relied much more heavily on tree ring records for data, said another researcher who like Hughes worked on both this study and the earlier ones. The new study made much more use of other sources, including data sediments, stalactites and stalagmites from caverns and other things.

The original studies by Hughes and his colleagues led to a congressional investigation in 2005. That led directly to a National Academy of Sciences investigation.

In the academy’s 2006 report, it agreed with a critic of Hughes’ research that it is hard to quantify that one decade is hotter than any going back 1,000 years. But it said that there is high confidence that surface temperatures during the late 20th century were warmer than any comparable period over the past 400 years.

The problems with going back 1,000 years, the academy review panel said at the time, was a lack of evidence besides tree rings such as boreholes, ice cores and retreating glaciers.

By broadening their data-gathering, the latest study sought to address the academy’s concerns. The academy, by concluding that the earlier research was overly dependent on one type of data, had put “sort of an asterisk” on the earlier research, said Michael Mann, a Penn State University meteorology professor and colleague of Hughes on both the older studies and the new one.

“We sort of removed that asterisk,” because the new study’s conclusion didn’t depend as much on one kind of data, said Mann, director of Penn State’s Earth System Science Center.

The two earlier studies, published in 1998 and 1999, compared recent temperatures to those dating back first 600 years and then 1,000 years.

The latest study will be published Sept. 9 in the Proceedings of the National Academy of Scientists.