TUCSON, Ariz. (AP) - Did global warming spur severe drought in the Western United States? A new study co-authored by a tree-ring researcher at the University of Arizona shows a possible connection.

The width of tree rings over the past 1,200 years show that temperatures were unusually high during "megadroughts" between 900 A.D. and 1300 A.D., according to the study.

It said the era may be an indication of what's to come for the West as the planet keeps getting hotter.

"It's kind of a cautionary tale," said lead author Edward Cook of Columbia University's Lamont-Doherty Earth Observatory. "Any warming in the future, whether due to greenhouse gases or natural variation, would not be good for the West."

Global warming is at least partly due to heat-trapping greenhouse gases from tailpipes and smokestacks.

So will the Earth will keep getting warmer this century?

The study's authors note there's no proof global warming has caused the West's current dry spell.

"I think it's way too speculative to say that warming is in any way responsible for these last four years of drought," said David Meko, associate research professor at UA's Laboratory of Tree-Ring Research. "A four-year drought is a little blip in the tree-ring record."

But the scientists believe the synchronicity between the warm and dry periods wasn't just a coincidence.

They say the warmer temperatures are at least partly due to heat-trapping greenhouse gases from tailpipes and smokestacks. And they suspect higher temperatures made the eastern Pacific resemble the La Nia pattern that typically makes the West drier than normal.

The study is scheduled to be published in the journal Science in the next few weeks. It was reported earlier this month in the prestigious publication's online edition.

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Information from: Arizona Daily Star, http://www.azstarnet.com