The American south-west and central plains could be on course for super-droughts the like of which they have not witnessed in over a 1,000 years.
Places like California are already facing very dry conditions, but these are quite gentle compared with some periods in the 12th and 13th Centuries.
Scientists have now compared these earlier droughts with climate simulations for the coming decades.
The study suggests events unprecedented in the last millennium may lie ahead.
There is already broad agreement that the American Southwest and the Central Plains (a broad swathe of land from North Texas to the Dakotas) will dry as a consequence of increasing greenhouse gases in the atmosphere