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California suffered a drought lasting several centuries during a period of global warming in the Middle Ages, a U.S. climatologist says.

Scott Stine of California State University in Hayward wrote in the science journal Nature that his findings could have implications for scientists studying the effects of global warming now believed to be under way."Here I present a study of relict tree stumps rooted in present-day lakes, marshes and streams, which suggests that California's Sierra Nevada experienced extremely severe drought conditions for more than two centuries before AD 1112 and for more than 140 years before AD 1350," Stine wrote.

This coincided with a long-term period of generally warm temperatures that has been recorded around the world, he said. He found similar evidence of drought in Patagonia, in present-day Argentina.

Stine suggested worldwide climatic conditions may have been altered by the warmer weather, changing wind patterns. Scientists have already warned that global warming could have similar effects today, turning forests into deserts, flooding coastal areas and disrupting weather in general.

"California's medieval precipitation regime, if it recurred with today's burgeoning human population, would be highly disruptive environmentally and economically," Stine wrote. "This emphasizes the importance of considering changes in precipitation, rather than simply in temperature, when weighing the potential impacts of future global climate change."