May 9, 2013 at 2:03 PM ET
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.
Assuming the interpretation is correct — and it is consistent with other research — she added, then the models currently used to forecast future climate underrepresent the power of carbon dioxide to warm the planet.
Brigham-Grette hopes that the modeling community can tune its parameters to better match her team's data "so that we can have faith that they are doing the best job possible of making projections into the future," she said.
The 1,043-foot-long (318-meter) sediment core is a story book of environmental change ever since a meteorite plunged into northeastern Russia some 3.6 million years ago and blasted out an 11-mile-wide (18-kilometer) crater that then filled with water.
Key to the story are bits of pollen from Douglas fir and hemlock, types of evergreen trees, that grew around Lake El'gygytgyn, about 62 miles (100 kilometers) north of the Arctic Circle. The pollen tells researchers what vegetation grew there, which in turn paints a picture of how warm and wet it was.
In the Middle Pliocene, the record suggests summer temperatures were around 59 to 61 degrees Fahrenheit (15 to 16 degrees Celsius) and annual rains of about 24 inches (60 centimeters).
It allows a "reconstruction of the way the world was," Mark Pagani, a geologist at Yale University, who was not involved with the new research, explained to NBC News. "It is really useful; it is not a model anymore."
The analysis from this and other studies suggests that the carbon dioxide already in the atmosphere has baked several degrees of warming into the climate system, which is in the slow process of reaching a new balance. "You have to wait awhile if you want to see how warm it can get," Pagani noted.
Brigham-Grette and colleagues detail a time series from the lake sediment core in a paper published online today in Science that focuses on the transition from the warmer, wetter Arctic of the past to the beginnings of the last ice age, known as the Pleistocene.
Earlier work indicated that glaciers started to form in the Arctic during the Pliocene, but the Lake El'gygytgyn sediment core suggests that "it is too warm in the summers to preserve the ice," Brigham-Grette said. "We don't start getting summers colder than present until about 2.5 million" years ago.
Going forward, the sediment core should allow the research community to refine its understanding of what the onset of glaciation looked like — perhaps a slow start with a scattering of small glaciers, she noted.
"That's the academic question: what drove us into glaciation," Brigham-Grette said. "The more practical one for the world today is understanding what the response time of the planet is to increasing greenhouse gases."
"And this new record from the Arctic is going to show that in fact it is quite reasonable to expect the warming we are seeing now to actually have major changes in the high latitudes."
John Roach is a contributing writer for NBC News. To learn more about him, visit his website.