Implications
Even at today's slightly elevated temperatures, with a rise of around half a degree centigrade, mountain glaciers are receding significantly, as also seem to be, locally, the margins of the ice in Greenland and Antarctica. The Greenland icecap is vulnerable, and its loss would mean a sea level rise of some 7 metres; as it creates its own regional climate, its loss may be effectively permanent. In Antarctica, the recent break-up of ice shelves has precipitated increased streaming of ice from much farther inland, which potentially represents the initiation of a phase of much more serious ice-sheet collapse.
This recently observed behaviour has shown clearly that ice-sheets are not relatively inert masses responding sluggishly to temperature change. Rather they are now perceived in much more dynamic terms, showing strong - and potentially dangerous - responses to small changes in external conditions. This would accord with geological evidence indicating past ice-sheet collapses, releasing 'iceberg armadas' and causing sea level rises of several metres in a decade.
The threat to humanity is clear: such a disappearance of living space (with some 100 million people living within less than 1 metre above present sea level) would represent a virtually impossible burden to a human population that is already struggling to feed itself, and is set to add another three billions to its numbers this century.
We note that it may not be the amount of sea level rise, as its speed, which may be catastrophic for a large section of humanity. The geological record shows that the melting of icecaps does not proceed smoothly, but occurs in fits and starts. Thus, the last retreat of the great ice-sheets included at least three episodes where sea level rose some 5-10 metres within the space of a decade. This is because a modest sea level rise can destabilize the edge of a mass of land ice, causing large parts of it to rapidly slide into the sea.
The consequences of such a sea level rise would be calamitous, comparable (and perhaps including as a consequence) a global war. Unlike a world war, though, civilization cannot get back to normal afterwards, as much of the landscape will have been drowned, effectively forever. We consider the threat to be imminent, the timescale of the global changes seeming likely to include the lifespans of our children.
Global warming: A Perspective from Earth History
ebulletin University of Leicester
Dr Jan Zalasiewicz (Chair), et al.
Stratigraphy Commission of the Geological Society of London
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'We don't have much time'
Jan Zalasiewic/Guardian UK
26.Nov.04
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