Sometime in the past 1.1 million years, the thickest part of the Greenland Ice Sheet melted completely, scientists said in a study released today that analyzed fossilized bits of moss, wood shards, insect and fungi fragments, as well as the seed of an Arctic poppy.

The samples, gathered decades ago from beneath 2 miles of ice, show there was a rocky tundra landscape in central Greenland, with patches of moss, willows, flowers and bugs, when the ice melted at a global average temperature close to the level projected for the end of this century.

If the ice covering the center of the island was melted, he said, then most of the rest of it had to be melted too, “and probably for many thousands of years, enough time for soil to form and an ecosystem to take root.”

“We now have direct evidence that, not only was the ice gone, but that plants and insects were living there,” he said. “And that’s unassailable. You don’t have to rely on calculations or models.”

Similar evidence came from a 2016 study showing a “cosmic ray burn” in Greenland rocks that are also now covered with two miles of ice, “from a time within the last million years or so, when temperatures were not much higher than now,” said Richard Alley, a Pennsylvania State University geoscientist who was not involved in the new study.

“The new paper confirms and extends that information, showing that the ice was gone long enough to establish a tundra ecosystem recognizably similar to cold modern ecosystems,” he said. The record doesn’t show the exact temperature or how fast the ice melted, but the new study “confirms that a lot of sea-level rise occurred at a time when causes of warming were not especially extreme, providing a warning of what damages we might cause if we continue to warm the climate.”

Co-author Halley Mastro, a paleoclimate researcher at the University of Vermont, spent long hours studying the biological remnants under a microscope, and said the finding was not a total surprise. Previous studies from the same core sample of gas bubbles in ice layers above the sediments had elevated levels of organic compounds like nitrogen that couldn’t be explained with atmospheric variations, leaving ground-level organic material as the likely source.

Like Bierman, Mastro thinks the organic sediments date back to an interglacial period about 400,000 years ago, when carbon dioxide levels were probably much lower than today, but summertime temperatures were higher and ocean currents quite different than now. Comparable samples taken under thinner ice, at Camp Century in northwest Greenland, were stored in a way that enabled more accurate dating.

Greenland Meltdown Already Intensifies Climate Extremes

Research published in January 2024 showed that scientists had previously been underestimating Greenland’s rate of ice loss by about 20 percent, and other recent studies show new threats, like huge areas of accumulating slush, as well as an increase in extreme rainfall and a newly documented web of micro-cracks on the ice sheet that could also speed melting.

Along with raising the level of oceans, water flowing into the North Atlantic from Greenland’s melting ice and other parts of the Arctic is also contributing to extreme weather in Europe, according to a March 2024 study. And that same influx of icy water is probably also disrupting the Atlantic Meridional Overturning Current (AMOC), which carries heat from the equator toward the Arctic. A failure or significant weakening of the AMOC would have disastrous climate consequences, especially in Europe, including the potential collapse of agriculture in northern Europe. 

Bierman said global warming is eating away at the ice sheet edges, but also melting it from the top, with worrisome feedback loops. At the periphery, when the ice melts, it exposes darker rocks and ground that heat up and accelerate the melting of the edges. And as the elevation of the top of the ice sheet drops, it warmer layers of the atmosphere also speed melting.

As the ice sheet summit lowers, eventually snow will stop accumulating, and “that’s the end of the ice,” he said. “I think that’s the real fear, why we should be frightened.” 

In 2023, scientists showed conclusively that the 2000-2010 period was the warmest decade on record in at least 1,000 years on the surface of the ice at the summit of the Greenland Ice Sheet. 

Joseph MacGregor, a research scientist with the NASA Goddard Space Flight Center, who was not involved in the new study, said scientists had already suspected that the ice sheet melted during one of the interglacial periods in recent geological history. 

The new study bolsters the case that “Greenland’s landscape could look very different in a few generations if anthropogenic warming continues its present path,” he said.

“The common and still relatively popular perspective is that the Greenland ice is more stable than parts of the Antarctic Ice Sheet,” he said. “That may still be true, but Bierman’s study helps build the case that the Greenland Ice Sheet is still quite sensitive to warming.”

Bierman said none of the Greenland changes should be a surprise to anybody who’s been watching and listening to science during the past few decades, “but the rapidity at which it’s caught up to us is a bit surprising.”