Science Daily reports a week ago that the Pine Island Glacier, in Antarctica, is thinning four times faster than it did ten years ago. Gareth Renowden at Hot Topic pounces on this news with an enthusiastic lack of scepticism and hastens to paint it as alarming, saying:
At this rate of thinning, the glacier could disappear in 100 years, instead of the 600 years earlier estimates had suggested.
Although that merely confirms the error in the previous estimate. To raise alarm, one should always quote facts, even out of context, so he says:
Since 1994, the central portion of the glacier has thinned by as much as 90 metres, and the ice surface is currently lowering by 16 metres a year.
These useful facts are not in the link he provides, they’re from a report by the BBC, though Gareth doesn’t say so. He quotes a scientist saying material is being lost from the Pine Island Glacier at “an exponential rate” and says:
Given concerns about the stability of the West Antarctic ice sheet as the world warms and sea level rises, the words “exponential rate” sound particularly ominous…
So he links it directly with “global warming”, but in loose, ambiguous terms he can easily deny if challenged. The clear intention is to alarm. He unsurprisingly fails to mention that both the Science Daily report and the press release from Leeds say (my emphasis):
Scientists believe that the retreat of glaciers in this sector of Antarctica is caused by warming of the surrounding oceans, though it is too early to link such a trend to global warming.
There is simply no justification to link this (so far unseen) paper with global warming when the scientists themselves fail to do so. He also claims sea level is rising, so we ought to point out that globally, sea level rise has levelled off and levels have not risen since about 2005. Whatever this glacier has done, it is not presently affecting sea level.
A recent (Feb 2009) paper, “Increased rate of acceleration on Pine Island Glacier strongly coupled to changes in gravitational driving stress,” from the British Antarctic Survey, about the inland glacier (i.e. not the floating part), concludes:
Acceleration is highly correlated to slope increase and no sustained increase in longitudinal stress gradient, or decrease in basal drag, is needed to explain the force balance.
So far as I can see, that means nothing more dangerous than that a steeper slope is making the glacier slide downhill faster. Heavier bodies slide more quickly than light ones. That paper says nothing about “global warming” to explain the increased speed, because the only reason glaciers move at all is in response to gravity.
So the Pine Island Glacier seems to be thinning at the moment. For the floating portion, that could mean imminent retreat of the snout, as calving might occur quicker with thinner ice more easily broken by the movement of the sea. We can expect the inland portion to slow down as it loses mass — good news for those fearful of sea level rise.
But, if the glacier is thinning, where’s the missing water?
If it fell as snow elsewhere, there could be no net effect on sea level for several hundreds or thousands of years. If it rained elsewhere, it would add something to sea level after evaporation, absorption and storage. If it’s still in the atmosphere, it has not yet increased sea level. If it failed to fall hundreds of years ago, thereby depriving the glacier of mass, it has already done whatever it was going to do and we can disregard it; we are not told how long it takes the Pine Island Glacier to traverse its course to the sea.
However if the glacier was melted from underneath by warmer water, it was floating, so the melting added nothing to sea level. There’s a lot we don’t know about glaciers and sea level.
But there seems no reason for alarm, Gareth.
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