Global warming could have halted a new glaciation that had already begun about 2,000 years ago. This is the main conclusion of an investigation published on October 22 in the scientific journal Science, which has reconstructed the evolution of an ancient ice mass located in the Canadian Arctic and has discovered that its expansion was interrupted during the 20th century, coinciding with the rise in temperatures caused by human activity.
The work, carried out by researchers from Columbia University and other international scientific institutions, focuses on the Barnes ice cap, located on Baffin Island, in Canada. It is the last great vestige of the ancient Laurentide ice sheet, which during the last glaciation covered much of North America and reached thicknesses of over three kilometers. According to the scientists, this ice cap began to regain surface area about two millennia ago, in a process of natural cooling that could have represented the first steps toward a new expansion of the continental ice sheets.
However, growth stopped around 1960, when warming summers began to cause a greater loss of ice than the amount accumulated during the winters. Since then, the ice cap has retreated and scientific models indicate that it could disappear completely during the coming centuries. The discovery has opened a relevant question for climatology: whether humans have been capable of interrupting one of the longest-lasting and most regular natural processes in the climatic history of the Earth.
A ice cap in Canada reveals the possible beginning of a new glaciation
The research has focused on the Barnes ice cap, located on Baffin Island, within the Canadian territory of Nunavut, one of the northernmost regions of America. Although it currently occupies an area comparable to that of the U.S. state of Delaware, it constitutes what remains of a mass of ice that once extended from the Arctic Circle to areas of the current state of Illinois.
During the last great glaciation, the Laurentide ice covered enormous extents of Canada and northern United States. Its retreat occurred as temperatures rose at the end of that cold period, about 11,700 years ago. However, a small part of that structure survived in the Canadian Arctic, where climatic conditions allowed the Barnes ice cap to be preserved.
The researchers have discovered that the ice mass reached its minimum dimensions about 3,600 years ago and began to expand again about 2,000. This growth was slow, but sustained over centuries, and is especially significant because it coincided with a natural reduction in the solar energy that the northern hemisphere receives during the summer.
According to the team led by geochemist Nicolás Young, of the Lamont-Doherty Earth Observatory at Columbia University, this behavior could represent the beginning of a new glacial period. The expansion of the ice would have continued for thousands of years if climatic conditions had maintained their previous evolution, although that interpretation depends on how the start of a glaciation is scientifically defined.
How scientists discovered that the ice was advancing 2,000 years ago
One of the particularities of the research is that the scientists have managed to reconstruct thousands of years of ice evolution through the analysis of ancient plants and mosses preserved beneath the glaciers. The Barnes ice cap is frozen directly onto the rock, which limits its movement and makes it possible to preserve plant remains that were buried when the ice advanced over them.
When a tundra area is covered by a glacier, the plants that grew in that land die and remain trapped beneath the ice. If centuries later the glacier retreats and exposes those remains, the researchers can analyze their age using carbon 14 dating techniques. This procedure makes it possible to approximate the moment when the ice first covered a given surface.
The team combined these analyses with other geological techniques, including the measurement of beryllium 10 in the rocks, which helps determine how long they have remained exposed at the surface. The comparison of the results made it possible to reconstruct the initial retreat of the ancient ice sheet and its subsequent expansion.
The researchers also used samples obtained from other small ice caps in the same region. The data indicate that the new expansion began approximately 2,000 years ago and continued until the mid-20th century, when the process reversed. The current retreat is exposing land and plant remains that had remained frozen for centuries, offering new evidence about the evolution of the Arctic climate.
20th-century warming interrupted the growth of the ice
The turning point occurred around 1960, when summer temperatures rose enough to break the balance between the snow accumulated during winter and the ice that was lost in summer. Until then, the ice cap had maintained progressive growth, but from that moment it began to register net mass losses.
Scientists relate this change to the warming caused by the increase in concentrations of greenhouse gases, especially carbon dioxide released by the burning of fossil fuels. Human influence ended up prevailing over the natural cooling trend associated with the planet's orbital variations.
The research indicates that the expansion of the ice had continued despite the warming produced by greenhouse gases already beginning to offset part of the natural cooling. However, the acceleration of industrial emissions ended up altering that balance and caused the retreat of the glacial margins.
"It was beginning, everything was normal, the next glaciation was about to occur and, nevertheless, it stopped", Nicolás Young explained when presenting the results. For the researcher, the phenomenon constitutes a demonstration of the capacity of human activity to modify climatic processes that develop over thousands of years.
The study maintains that the evolution of the Barnes ice cap offers physical evidence of that change. However, observing the retreat of a specific mass of ice does not by itself prove that the entire Earth was inevitably entering a continental glaciation. That is the broader interpretation proposed by the authors and one of the main elements of scientific debate raised by the work.