In an unusual new study, scientists say they have detected the fingerprint of human-driven global warming on patterns of drought and moisture across the world as far back as 1900. Rising temperatures are well documented back at least that far, but this is the first time researchers have identified resulting long-term global effects on the water supplies that feed crops and cities. Among the observations, the researchers documented drying of soils across much of populous North America, central America, Eurasia and the Mediterranean. Other areas, including the Indian subcontinent, have become wetter. They say the trends will continue, with severe consequences for humans. The study appears this week in the leading journal Nature.