Using studies of tree rings going back centuries, scientists have unearthed clear evidence that the rise of human-generated greenhouse gases was having an effect on global drought conditions as early as 1900.

A new, first-of-its-kind study by scientists at Columbia University’s Earth Institute, published Wednesday in the journal Nature, largely confirms what climate models have shown. In the absence of strong historic data on precipitation, those computer models forecast not only future scenarios, but shed light on historical trends.

The dovetailing of the tree-ring studies, which correlate to soil moisture, with climate models gives scientists the assurance that the computer models are, in fact, correct, they say.

“These tree-ring reconstructions let us go back in time and get a