Plants Buried Under a Canadian Ice Cap Show Glaciers Had Started to Regrow

Plants preserved under a shrinking ice cap on Canada's Baffin Island suggest that glaciers in the region were growing again well before industrial warming, according to a study published in Science. New Atlas, reporting on the Columbia University research, said the team argues the Arctic may have been at the start of a new glaciation when human-caused warming interrupted it.

The finding does not mean a new ice age was certain to arrive. It is evidence from a single corner of the planet, and the researchers say it gives climate models something to explain.

How buried plants revealed the ice's history

A team led by Columbia University geochemist Nicolás Young studied Barnes Ice Cap, the last surviving remnant of the Laurentide Ice Sheet that covered much of North America during the last glacial period, New Atlas reported. As the huge ice sheet retreated, plants colonized the exposed ground, and were buried again when the ice advanced. Because there was little movement in the ice above, the plant material was preserved relatively well. Today's retreating ice is giving those plants back.

The researchers produced 88 new radiocarbon ages from the previously buried vegetation. Because the ratio of radioactive to decayed carbon changes after an organism dies, each measurement estimates when advancing ice killed the plants at that spot. Mineral samples added another clue: beryllium-10 builds up in exposed rock through interactions with cosmic rays, which indicates when the ice first pulled back.

A timeline of growth, retreat and regrowth

• Roughly 3,600 years ago: the edges of the Laurentide ice had withdrawn inside the recent boundaries of Barnes Ice Cap before expanding again.
• Roughly a thousand years ago: the plant record documents the ice's expansion up to about this time. Another 186 previously published radiocarbon dates from neighboring ice caps suggest the glacier began regrowing around a thousand years before that.
• Mid-20th century: Barnes Ice Cap reached its largest extent in recent history, before retreat exposed the vegetation used in the study.
• Since around 2010: the elevated accumulation zone that once kept part of the ice cap's surface high enough to gain snow has disappeared.

Why a new glaciation may have been starting

The timing fits a familiar pattern in Earth's climate, New Atlas reported. Slow changes in the planet's orbit and axial orientation shift how sunlight is distributed. Cooler summers let more winter snow survive, which builds ice that reflects more sunlight and reinforces the cooling.

Young and his colleagues argue that the renewed growth could count as a glacial inception, the point when an ice sheet starts to grow again after an interglacial minimum. “It's a very powerful example of how we have jolted the system,” Young said.

The question of when the current warm interval would have ended without industrial activity has been debated. A 2016 modeling study in Nature suggested an inception was “narrowly missed” before the Industrial Revolution and that, without human interference, the current interglacial could have lasted another 50,000 years, according to New Atlas.

What this means for the ice and for climate research

Evidence from one location does not show that growing glaciers would have merged into continent-spanning ice sheets again, and the reconstruction leaves that later path open. Whether the earlier growth marks the formal beginning of another glaciation remains a matter of interpretation and scale.

What is happening now is clearer. Rising summer temperatures are removing more ice from Barnes Ice Cap than winter snowfall replaces, and rising carbon dioxide from human activity has sharply sped up the warming. Projections suggest this remnant of a once-great ice sheet will melt entirely within the next few centuries.

Around Prague, based on reporting by New Atlas