About 3 million years ago, evergreen forests — not tundra — carpeted the Arctic, Greenland was green, and sea ice only formed for a few months in the winter, if it formed at all, according to analysis of sediment pulled from a Russian lake.

“Where we are going is into this warmer world,” Julie Brigham-Grette, a geologist at the University of Massachusetts Amherst, told NBC News.

At the time — the Pliocene — concentrations of the greenhouse gas carbon dioxide were around 400 parts per million, the same as they are today. But Arctic temperatures were about 14.4 degrees Fahrenheit (8 degrees Celsius) warmer than today, explained Brigham-Grette, who led the analysis.