Steve McIntyre is back, posting on the latest exchange between Jay Zwally, who recently published a paper saying that Antarctica is gaining ice, and Jonathan Bamber, who attempts a rebuttal over at Real Climate. McIntyre shows that Zwally’s position is worth considering and that Bamber’s criticism is either naive or disingenuous. As usual, McIntyre’s post is careful and logical. It seems clear that although we can’t be certain, the balance of probabilities is that ice in the Antarctic is increasing, despite significant losses in the Western Antarctic Ice Sheet. That’s because the WAIS is small and the rest of Antarctica is large. Ice is increasing at a very small rate in the large part and decreasing at a rapid rate in the small part. Yeah, McIntyre explained it better.
The total is a drop in the bucket, almost literally. Zwally wrote in 2015 that ” that there had been ice mass gain gain of ~112±61 Gt/year over 1992-2001 and ~82±25 Gt/year over 2003-2008. ” Bamber doesn’t give an estimate at Real Climate, but says (incorrectly) that Zwally is an outlier and that additional lines of evidence suggest that Antarctica is losing mass, estimated by the IPCC in AR5 at an of 147 ± 74 Gt/year.
There are about 150 million Gt of ice in the Antarctic ice sheets. Antarctica won’t even notice either Zwally’s gain or Bamber’s loss. But will we?
It takes 361 Gt to raise ocean sea level by one millimeter, 9,137 Gt to raise sea level by one inch. So, at the current rate of even the IPCC’s view of loss, not any time soon.
But that’s not what we’re worried about. The Western Antarctic Ice Sheet is not stable and may disintegrate over a period of 100-200 years, although this disintegration has not yet started. That’s the reason that the WAIS figures in climate conversations.
But this has nothing to do with climate change. As T. Hughes wrote in 1973, “A study of published data concerning the past and present ice cover of West Antarctica indicates that during the last few million years the ice sheet has been retreating in stages, each retreat stage being preceded by an advance of comparable duration. Thus disintegration of the west antarctic ice sheet seems to follow the disintegration pattern of other continental ice sheets and may be the last phase of the worrldwide Late Cenozoic ice age.” As Conway et al wrote in 1999, “Current grounding-line retreat may reflect ongoing ice recession that has been under way since the early Holocene. If so, the WAIS could continue to retreat even in the absence of further external forcing.”
This conversation, motivated by those wishing to attribute a drop in the bucket of ice melt to human contributions to climate change, is typical of the fevered state of the climate conversation. It is also insane.