Snow on snow: vanishing glacial ice

Winter’s white blanket of snow is becoming rarer. We must learn to appreciate it.

Antarctica is losing ice from coastal glaciers at a record rate. PHOTO Australian Antarctic Division

Antarctica is losing ice from coastal glaciers at a record rate. PHOTO Australian Antarctic Division


There could be no better description of how our planet begins its descent into an ice age than Christina Rossetti’s haunting 1872 Christmas carol: “Snow on snow, snow on snow, in the bleak midwinter long ago”.

Year after year snow stays longer on the ground, reflecting sunlight as it builds layer upon layer as subtle shifts in Earth’s axis and rotation around the sun cause a drop in mean temperature over thousands of years. Thus did mountain glaciers form, and ice sheets on polar lands.

It was on the edge of the world’s biggest ice sheet, in Antarctica, that I had my first and only experience of skiing. Large drifts on coastal sea ice were an ideal place for a timid novice to learn some basics without breaking a leg.

I never took up the sport, but that happy memory helps me understand why people put so much effort and money into chasing snow. And why, when the snow doesn’t come, they feel so let down.

The first appearance of snow on the ground, transforming dull browns and greens to a brilliant white, is for the child and the romantic in all of us. If you have to live with it for a while it’s possible to dislike it. But you can never be indifferent to it.

Snowfall often comes as a surprise because it’s hard to predict. The Australian ski season got a lift with the weekend’s snow and ought to be in full swing pretty soon, but the Bureau of Meteorology cannot say with any assurance how things are going to pan out.

The global long-term picture is clearer, with today’s small downward trend in snow cover set to become more pronounced. Mean snow cover will become less deep, less extensive, and of shorter duration in coming decades with higher winter temperatures and more erratic precipitation.

Science is telling us Australia should anticipate a relatively rapid decline in snow cover. Altitude is a telling factor, and that’s something this country doesn’t have.

Tasmania’s low-altitude ski slopes are most vulnerable, but the higher mainland fields are little better off. A Victorian study out last week anticipates most resorts will close by mid-century. By 2100 skiing on natural snow in this country is likely to be just a faded memory.

The much younger, much higher Southern Alps will ensure New Zealand’s skiing industry survives longer, but its diminishing mountain glaciers remind us that nowhere is safe from climate change. Last summer’s record warmth there saw some glaciers retreat hundreds of metres.

Plenty of people other than skiers worry about glaciers. Disappearing ice in the Himalayas and Andes is causing real hardship for people downstream, while the fate of Greenland and Antarctic glaciers is a nagging worry for all the world’s coastal dwellers.

The scale of the glaciers that drain the Antarctic ice sheet is almost beyond imagining. The largest ones could swallow up an average-sized European country, with an ocean frontage stretching over the horizon. Their fate is linked inextricably with that of coastal lands everywhere.

Antarctica was a late starter in responding to global warming, decades behind Greenland. Since 1992 melting of glaciers and coastal ice shelves has contributed 8 mm to global sea level, but on a steadily warming planet the Antarctic contribution will eventually be measured in metres.

Last week a team of 84 scientists from over 40 international organisations, including some from Australia, released a combined verdict on what is currently happening there.

The news is not good. They found that Antarctica’s ice sheet currently sheds over 200 billion tonnes of ice into the ocean each year, which equates to half a millimetre a year of global sea level rise.

The ice sheet’s melt rate is now three times what it was 15 years ago. Parts of the continent, notably the Antarctic Peninsula, are experiencing melting at five times the level in the 1990s.

This is not what nature intended. Our planet has been relatively cool since modern glacial-interglacial cycles began 2.6 million years ago. The present state of our ever-changing relationship with the sun tells us we should soon be starting a very slow descent into another glacial period.

But the more powerful forcing of man-made greenhouse warming has disrupted that pattern. Science has calculated that left unchecked, our emissions will delay the next glaciation for at least 500,000 years, and indefinitely if emissions remain unmitigated.

All the humans who ever lived, and all of our humanoid ancestors, knew only a world that includes ice and snow. If we bring about the end of the ice ages we will truly be living in a new world.

The skiers are right. We need snow – snow on snow, in fact – to replace lost glacial ice. With David Walsh and Dark Mofo, we should wholeheartedly celebrate bracing winters. They become more precious with each passing year.

This entry was posted in Antarctic, carbon emissions and targets, changes to climate, climate sensitivity, glaciology, marine sciences, modelling, palaeoclimatology, science, sea level. Bookmark the permalink.

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