The ice of Greenland is melting, and the difference is discernible in our sea levels. [15 October 2013 | Peter Boyer]
As a child I’d spend hours studying maps and pondering what lay behind them. I recall being intensely fascinated by a strange land mass, clearly much bigger than Australia, at the top of the world map. Greenland was its name, and I imagined it as a forested land like tiny Tasmania.
I eventually worked out that its huge size on the map was a trick of Mercator’s projection, that in area it was actually somewhere between Western Australia and Queensland, and that it wasn’t really a green land, but a white one.
Greenland and its southern counterpart, Antarctica, are known for their great expanses of ice, the two biggest ice sheets in the world — so wide and deep as to seem everlasting.
But both lands were once ice-free, and will be again. It won’t be in our lifetimes or for thousands more years, but they’re showing early signs of throwing off their frozen overburdens. The state of Greenland’s ice is now recognised as being a key indicator of global climate change.
When it’s cold enough for snow to stay on the ground long enough to be covered by more snow, and the process keeps repeating itself so that enough has accumulated to last through summers, the compressed snow eventually becomes an icecap. When this continues for thousands of years and covers a large area connecting many icecaps and the glaciers that flow off them, you get an ice sheet.
Antarctica’s ice sheets began to form around 35 million years ago, while the Greenland ice sheet is about half that age. They have fluctuated in size since then, but they never disappeared. They formed when declining atmospheric carbon dioxide crossed a threshold, sparked largely by shifts in Earth’s orbit around the sun. This led to colder temperatures and other climate feedbacks that caused ice caps to expand and join together.
The accumulating ice locked away vast quantities of water, enough to cause the sea level to drop by tens of metres. In the past few million years sea levels fluctuated as ice ages came and went, but for thousands of years now, ever since humans have been growing crops, they’ve been pretty stable. Until now.
The 2013 report of the Intergovernmental Panel on Climate Change says it’s “virtually certain” that the rate of global mean sea level rise has accelerated over the past 200 years, from changes measured in tenths of millimetres a year to millimetres a year today. The IPCC reports that while sea level has risen since 1901 at an average rate of about 1.7 mm a year, the past 20 years have seen levels rise by over 3 mm a year, much of it caused by increased outflow from the Greenland and Antarctic ice sheets. Which means they’re getting smaller.
Hobart-based geomorphologist Chris Sharples makes a living out of studying the effect of the seas on coastal lands. For years he has mapped in detail the impact of rising sea levels, storm surges and changing currents on our coasts, first in Tasmania and then all around Australia. When he decided to spend part of the last northern summer in Greenland, the key role of this big island in global climate change was in the back of his mind. But most of all he was attracted by its wild, stark, beautiful landforms and the experience of humans there over thousands of years. His travels took him to the island’s west coast, where he traversed the narrow band of tundra between the edge of the ice sheet and the shores of Davis Strait before taking a ferry north to Ilulissat, near Greenland’s fastest-flowing glacier, Kujalleq, or Jakobshavn.
Sharples’ Australian coastal studies have focused on how moving masses of water affect specific coastal landforms, such as beaches, clay formations and cliffs that can be undermined. Greenland has some such issues, but there are much bigger ones in play there.
Unlike other parts of the world, the sea around most of Greenland’s coast is actually falling relative to the coast. Or rather, the land is rising because the icecap is getting lighter. In each year of the past decade, according to the IPCC, it’s lost an average of 215 gigatonnes (billions of tonnes) of ice. The whole Greenland ice sheet weighs more than 2.8 million gigatonnes, so at today’s depletion rate it would be many thousands of years before it’s all gone.
But with accelerating global carbon emissions, the IPCC expects the rate of Greenland’s ice loss to rise sharply. There’s little doubt, according to the IPCC, that in the decade to 2011 the annual contribution to sea levels of Greenland’s melted ice was over six times higher than through the previous 10 years. The report finds that in the years to 2100, out of a probable total sea level rise of about half to one metre, Greenland alone could contribute between four and 21 cm, well above the IPCC’s 2007 forecast of between one and 12 cm.
The 2013 summer in Greenland was close to normal, but each of the three summers before that were warmer than anything in the instrument and proxy records since at least the 1400s. In 2012, for the first time on record, it rained on the northern Greenland icecap. Receding ice has given Greenlanders much to be happy about, including better access to their land’s known mineral wealth. But it’s also convinced them that their climate in changing, massively and radically. As Chris Sharples reports, there are no debates there about a “warming pause”.
Sharples’ stories of his arctic wanderings took me back to my childhood fantasies of Greenland. White is the predominant colour for most of the year, but as his photographs show, with the summer melt the land is indeed green. As long northern summer days continue to warm, both the greening of Greenland and the ice sheet’s contribution to sea level will gather pace over this century and beyond. In the storytelling traditions of far-northern lands and peoples, this saga will be long in the unfolding.