Earth was sliding toward a new ice age beginning about 2,000 years ago, but human greenhouse gas emissions brought the continental cooling trend to an abrupt halt by the 1960s. Researchers uncovered the timeline by analyzing patches of dead vegetation preserved beneath the Barnes Ice Cap on Baffin Island.
The planet should be moving steadily toward a cooler climate driven by predictable variations in Earth’s orbit around the sun. Instead, anthropogenic greenhouse gas emissions have thoroughly overwhelmed those natural astronomical cycles. A study published in Science details how a modern ice age started at least 2,000 years ago only to be derailed in the mid-20th century.
It took thousands of years for the ice age to get itself into gear, and then it was halted abruptly.
Gifford Miller, Institute of Arctic and Alpine Research fellow
Vegetation Beneath the Barnes Ice Cap Reveals a Millennial Timeline
Physical evidence of the aborted glaciation emerged from dead vegetation trapped beneath the Barnes Ice Cap on Baffin Island. As retreating ice edges exposed long-dead mosses and small shrubs, researchers collected samples to establish when permanent ice last advanced across each location. Radiocarbon dating provided exact kill dates for the plants, which were crushed and smothered as the ice expanded.
Nicolás Young of Columbia University’s Climate School explained the underlying mechanics of the natural archive.
These mosses were growing on the landscape and then all of the sudden the ice cap expands and covers them. That radiocarbon age tells you the timing of when ice killed the plant.
Nicolás Young, geochemist at the Lamont-Doherty Earth Observatory
The analysis verified two primary hypotheses. First, the preserved plants died within the last 3,000 years, confirming that a new glacial cycle was underway. Second, plants located closest to the ice edge proved older than those further out, marking the steady outward march of a growing ice sheet. The data showed the ice cap began its expansion at least 2,000 years ago, reaching its greatest extent around 1960 before shrinking reversed the trend.
Tracing the Laurentide Ice Sheet and Regional Ice Caps
The Barnes Ice Cap is the final surviving remnant of the Laurentide Ice Sheet, a massive sheet that covered much of Canada and the northern United States between 95,000 and 20,000 years ago. Spanning outward from north of the Arctic Circle all the way down to Illinois at its maximum extent, the ice sheet also featured sections exceeding two miles in thickness. While the Laurentide repeatedly contracted and regrown across North America over the past 2.6 million years, researchers sought to determine whether the ice had ever shrunk smaller than its current Delaware-sized footprint on central Baffin Island in Nunavut before beginning to regrow.
Because glacial ice scours away geological clues as it advances, pinpointing the initial re-expansion point is exceptionally difficult. To solve this, scientists examined neighboring small ice caps across the same plateau that share identical climatic conditions. Data from nearly 200 kill dates gathered beneath those adjacent ice caps revealed none older than 2,000 years, establishing when regional re-expansion began.
What that means is that all of those ice caps up there didn’t start advancing or re-expanding until about 2,000 years ago. Since the Barnes Ice Cap is right next door, it’s probably a good bet that it also started expanding 2,000 years ago.
Nicolás Young, lead author and paleoclimatologist at the Lamont-Doherty Earth Observatory
Resolving a 1970s Scientific Debate on Incoming Glaciation
The newly published timeline addresses a historical puzzle from the 1950s and 1960s, when initial studies of the Barnes Ice Cap described an exceptionally stable glacier. Researchers now understand that era coincided with a rare moment of equilibrium, where decreasing summer solar radiation and rising greenhouse gas emissions temporarily balanced each other out.
Back in the 1970s, researchers converged at Brown University for a gathering centered on theories regarding the timing of the next upcoming ice age. Concluding that a glaciation period was imminent, the group transmitted a formal caution letter addressed to President Richard Nixon. Those warnings were later seized upon by climate skeptics to dispute global warming. The new study demonstrates that scientists were correct about a pending glaciation getting underway, but rising carbon emissions quickly overwhelmed the natural cooling cycle.
Gifford Miller experienced that period firsthand during a 1972 expedition south of Qikiqtarjuaq on Baffin Island, where sea ice never retreated and the researchers were stranded.
Projected Disappearance of the Barnes Ice Cap
Edges of the Barnes Ice Cap have retreated an average of 4 meters per year since the 1980s, driven by elevated carbon emissions. The ice cap has retreated 200 to 800 meters since 1960.
The disappearance of the Barnes Ice Cap will erase the natural seed from which past continental ice sheets regrew, meaning if continental ice sheets ever begin to grow again, they may have to start without it.
