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Human activity was changing the Earth's drought and rainfall patterns as far back as the early 20th century, new research shows.

Drying in many regions, the researchers suggested, will get worse, with sobering implications for feeding the planet’s billions of people.

The new paper tracks long-term patterns of moisture levels in soil across regions of the world, including North America, Central America, Eurasia and the Mediterranean. The researchers found a “fingerprint” of human effects from producing greenhouse gases, as distinct from natural variability, as far back as 1900.

Scientists have long known that the planet has shown an overall pattern of warmer temperatures since that time — the phenomenon is the subject of a famous cartoon by Randall Munroe — but the new research shows the effects of that warming correlate with drier soil in some parts of the world and wetter soil in others. Climate scientists have long suggested that in a warming world, dry parts of the planet will become drier and wet parts of the planet will become wetter.