Sunday, May 04, 2008

Sea Ice Continued

A friend of mine sent me a pointer to an interesting online article written to clarify some of the technical controversies endemic to climate change debate. I learned the following:
  • yes; it is acknowledged that some scientists have argued that sea ice in the Antarctic has increased until 2002.
  • the increase is possibly due to changing wind patterns due to the hole in the Ozone.
  • less warm air in the interior causes more ice to accumulate in the winter.
  • in contrast, on the exterior, sea ice is shrinking overall.
  • By 2006, the overall total is lower.
First, let me emphasize that sea ice on the exterior floats (e.g. the Wilkins Ice Shelf) so overall sea levels are inelastic with respect to changes in exterior ice. Second, the Ozone story is post-hoc interpretation; it is not science. Soft scientific analysis is only impressive when it makes successful and risky predictions. How did climate scientists do on that score? In 2006, it was reported that the total amount of ice was shriking at an alarming rate:

THE first survey of gravity changes caused by the Antarctic ice sheet has confirmed that it is shrinking at an alarming rate.
I turns out that the scientists looked at 2002-2005 data and yes, over that time that the total sea ice (mass; as opposed to area) in the Antarctic was indeed shrinking. Woops! If they had actually bothered to consider past data they would have seen the reality for what it is: changes that are well within the limits of natural variation. In fact, 2005 was an unusual large drop in area (as it can easily be seen from my previous graph) and that should have been noticed. A good analysis would have predicted some regression back to the overall mean in area (all the more so if the Ozone hole theory were taken into account). Three more years later and we are right back on the general increasing trend. Yet, our "climate change" guru has this to say

A more recent study based on satellite measurements of gravity over the entire continent suggests that while the ice sheets in the interior of Antarctica are growing thicker, even more ice is being lost from the peripheries.
Alas; the study was not current by the time this was written. It was already contradicted by current data and now with the 2008 numbers it seems that the point is wholly wrong.


At 1:31 PM , Blogger Abhishek said...

Nature has had some interesting articles on natural variation in climate
v453/n7191/full/453043a.html (with links to various other articles)

The first article talks about how the ocean currents play a role in creating natural climate variations. Keenlyside et. al. predict that the effect of greenhouse gases will lead to weakening of meridional overturning circulation (MOC), and lead to a dip in the temp in the North Atlantic. The other study (article 2) finds that around 3.5 million years ago the ice-sheet at Antarctica might have totally disappeared for a span of around 200,000 years.

It would be interesting to see how with limited data (a century or so?) predictions will be made of variations which might have natural cycles of decades, centuries or millennia.


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