Researching climate in the Arctic, an international team of geochemists has finally hit pay dirt.

Digging up layers of ancient lake sediment and residue from glacial ice, they have pieced together a detailed temperature history of the Arctic over the last two thousand years.

Close analysis of these sediments has confirmed scientists’ suspicions that the Arctic had slipped into a long cooling phase at the turn of the first century A.D. Summer temperatures dipped steadily lower, decade-by-decade, until the nineteenth century as the industrial revolution took hold. The Arctic then began to warm, the study says, and has been warming steadily since.

Until lake sediments are dug up and analyzed, or trees hewn and their rings counted, scientists must turn to computers to simulate temperature histories of regions like the Arctic. Now, the computer calculations and physical data match, proof of the dependability of computer models for historical temperature reckoning and future forecasting.

Darrell Kaufman, lead author of the study, is very pleased with his team’s results. “All of our projections for the future are dependent on the models we have now,” he says. “Our paper is a huge step in demonstrating the success of computer models in predicting climate.”

Coinciding with a marked increase in greenhouse gas emissions, the phenomenon of Arctic warming is one more grain in a growing mound of evidence that shows the effects of human activities on global climate.