Data from some 50 spacecraft using a variety of techniques to monitor ice sheets show a worldwide retreat in the face of rising global temperatures.
However a detail from a recent news report on ice loss struck me as being very interesting: All the ice lost from Greenland and Antarctica in the past three decades could be represented as a cube 20 km on its side. Just compare that to the height of Mt Everest – about 9 km. That’s a lot of ice.
A 20 km cube is a lot; 7,560 billion tonnes of it actually. Two thirds of it comes from Greenland with the rest from Antarctica. Greenland is melting, Antarctica is being chipped away at the edges. The combined volume of ice in Greenland and Antarctica is about 32,900,000 cubic km. Hence a 20 km cube (8000 cubic km) represents a loss of only 0.024%, over three decades.
Looked at in absolute terms that doesn’t appear that much. It has contributed to an estimated 22 mm in global sea level rise. But at what stage does this slow melt become just interesting rather than alarming? One the face of it 0.024% over 30 years doesn’t seem something to unduly worry about, after all nobody would expect ice volume to remain constant in any realistic situation of climatic change.
The main point I took from the report is that ice loss seems to be a global phenomenon. What’s happening in Greenland and Antarctica is part of a global pattern.
Another recent report comes from the Cryosat satellite which takes a global view of the 200,000 or so glaciers on earth (excluding Greenland and Antarctica). It concludes that 2,720 billion tonnes of glacial ice have been lost in the past decade. But what is that expressed as a cube of ice? It would be a cube 14.6 km on its side, or 38% of the volume of our original 20 km cube. The researchers say it represents a 2% loss in a decade. Would we be worried if it was a 1% change? And if we observed at 2% increase instead, would we be worried about a looming ice age?
On one hand these volumes of ice are relatively small. On the other, these figures show how sensitive sea levels are to the melting of relatively small volumes of ice.
Not so long ago the place where I write this (southern England) was uninhabitable tundra, not far from the greatest southerly reach of Ice Age glaciers. Thanks to globally rising temperatures England today has become a green and pleasant land. The Earth has never been unchanging, but now we have the most sophisticated technologies to measure even the smallest and most gradual changes, using a multitude of parameters and features that respond to even modest changes in temperatures and the environments. What is more, we have become hyper-sensitised to those changes and are apt to extrapolate them far into the future – over longer timespans than just few years or decades and anticipating changes far more rapid and far more than one percent.