Drawing one of the strongest links yet between global warming and human conflict, researchers said Monday that an extreme drought in Syria between 2006 and 2009 was most likely due to climate change, and that the drought was a factor in the violent uprising that began there in 2011. The drought was the worst in the country in modern times, and in a study published Monday in Proceedings of the National Academy of Sciences, the scientists laid the blame for it on a century-long trend toward warmer and drier conditions in the Eastern Mediterranean, rather than on natural climate variability