Moss that froze under the ice caps of Baffin Island tens of thousands of years ago is now melting out into daylight. In 2013 a team led by Gifford Miller of the University of Colorado Boulder radiocarbon-dated those plants and concluded that average summer temperatures in the Canadian Arctic over the past century are the highest in at least 44,000 years, and perhaps in 120,000 years.
Baffin Island and its shrinking ice caps
Baffin Island, in the Canadian territory of Nunavut, is the largest island in Canada and the fifth-largest in the world, covering about 507,000 km². Only around 13,000 people live there, mostly in Iqaluit, the capital of Nunavut, and in Inuit communities such as Pond Inlet, Pangnirtung and Clyde River.
The island's interior is mountainous and icy. Mount Odin, the highest summit, rises to at least 2,143 metres, and Auyuittuq National Park holds Mount Asgard and Mount Thor, famous for one of the greatest vertical drops on Earth. The Barnes Ice Cap in the centre of the island has been retreating since at least the early 1960s, and the small high-altitude ice caps are thinning fast.
Radiocarbon dating ancient moss
When an ice cap forms over tundra, it freezes the plants beneath it in place and preserves them for as long as the ice survives. When the ice melts back, the dead plants reappear at its edge. Their radiocarbon age tells scientists when that ground was last ice-free, and therefore when summers were last as warm as today.
- The team collected 365 pieces of freshly exposed plant material from 110 sites along a 1,000 km transect across Baffin Island, at a range of altitudes.
- 145 samples gave usable radiocarbon dates.
- Most dated from the past 5,000 years, a period of strong Arctic cooling, but some had been buried 24,000 to 44,000 years ago.
Warmer than the early Holocene
The study, published in Geophysical Research Letters in October 2013, was the first to show that present Arctic warmth exceeds the peak of the early Holocene, which began about 11,700 years ago. At that time the summer sun delivered about 9 percent more radiation to the Arctic than it does today. The researchers also used Arctic ice-core records to reconstruct past temperatures. Warming has been under way for about a century, with the steepest rise since the 1970s.
"This study really says the warming we are seeing is outside any kind of known natural variability," Miller told Live Science. "All of Baffin Island is melting, and we expect all of the ice caps to eventually disappear."
Further information: Miller and colleagues: Unprecedented recent summer warmth in Arctic Canada
Video report on the study
Video: Study: Arctic Warmest It's Been In 44,000 Years (published by Secular Talk).
Explore more: checking a single Arctic melt-pond image; comparing glacier photographs across time. More stories on the Arctic.
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