"For example, a paper published Aug. 19 in Geophysical Research Letters by a scientist from the California Institute of Technology shows that even the apparently drastic decrease of summer-autumn Arctic sea ice is not unprecedented but merely an effect of Arctic Ocean geography."The paper, Geographic muting of changes in the Arctic sea ice cover, undermines the notion that AGW is a primary cause of decrease of Arctic sea ice in summer-autumn by showing that the actual mechanism is related to Arctic geography, which restricts the buildup of winter sea ice and thus shifts the semi-sinusoidal pattern of summer-autumn ice melt northward at a constant (not accelerating) rate of 8km/yr since the beginning of the satellite era in 1979. This explains why September Arctic sea ice extent has declined much more rapidly (1.1%/yr) than March sea ice extent (.26%/yr) since 1979.
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| March Arctic Sea Ice extent decreasing only 0.26%/yr |
References:
Explanation of the paper (translated from Icelandic)
A paper by the same author finds we are nowhere near a "tipping point" regarding Arctic Sea Ice
Even Tamino thinks the paper is correct
This is the author of the paper discussed in this blog post ("Geographic muting of changes in the Arctic sea ice cover"). Many thanks for your interest in my work. I want to clarify two points regarding my paper. First, the findings of this work, as summarized in the final two sentences of the paper, suggest that Arctic coastlines mute wintertime sea ice changes rather than amplifying summertime sea ice changes. In other words, these results say nothing to refute the well-known point that the summer minimum Arctic sea ice cover is rapidly retreating. Rather, they show that the wintertime sea ice cover is also rapidly retreating, from year to year, although this has not been as easy to notice due to the geography of the Arctic coastlines. Second, the findings of this work suggest that the Arctic sea ice edge moves poleward at a steady pace over the course of the year. From year to your, however, the pace does accelerate, consistent with previous studies discussing the acceleration of Arctic sea ice retreat. This can be seen, for example, in my Figure 3E.
ReplyDeleteIn a sentence, the results presented in my paper broaden the case for rapid and accelerating recent Arctic sea ice retreat. These results certainly no not undermine the notion that greenhouse-induced warming is a primary cause of recent Arctic sea ice changes. The Milwaukee Journal Sentinel piece that you link provides a completely inaccurate description of my paper (it is also worth noting that my paper says nothing about whether the decrease of Arctic sea ice is "unprecedented", as they write). The "Tamino" blog post that you link provides an accurate description of my paper.
The brief summary in your blog post of my separate paper on sea ice tipping points is accurate.
Ian,
ReplyDeleteThank you for your comments and clarifications. May I ask your opinions of the following?:
1. http://wattsupwiththat.com/2010/09/08/inconvenient-ice-study-less-ice-in-the-arctic-ocean-6000-7000-years-ago/
2. How is it possible for greenhouse gases emitting LWIR to heat the oceans, as outlined in the post
http://hockeyschtick.blogspot.com/2010/08/why-greenhouse-gases-wont-heat-oceans.html
Here is a summary of the paper from AGU Journal Highlights published today:
ReplyDeleteLandmass shape affects extent of Arctic sea ice
Arctic sea ice has retreated significantly in recent years, reaching a record low in September 2007. It is known that the seasonal cycle in Arctic sea ice extent is not symmetric—seasonal ice retreat proceeds gradually during early summer and then accelerates toward end of summer, while in winter, ice growth is rapid at first and then slows later in the season. Scientists have observed that ice cover has retreated far more rapidly in September than during other times of the year.
Some scientists have suggested that this seasonal asymmetry is due to factors such as temperature changes. However, Eisenman finds that the seasonal differences in rate of ice growth or retreat are caused by the geometry of the landmasses surrounding the Arctic Ocean. Because the Arctic Ocean is mostly surrounded by land, coastlines block the southward extent of sea ice growth during the winter, but coastlines have little effect on the extent of ice during the summer.
The author suggests that to better interpret changes in Arctic sea ice, instead of considering sea ice areal extent, scientists should track the line marking the latitude of the Arctic sea ice edge, averaged zonally over locations where the edge is free to move. He finds that this line moves northward or southward at a steady pace over the course of the year, with no seasonal asymmetry. In recent years, this line has been migrating northward at a rate of about 8 kilometers (5 miles) per year, consistent with overall ice loss. The study explains some aspects of the seasonal Arctic sea ice cycle and could help scientists better interpret sea ice evolution in the future.
Title: Geographic muting of changes in the Arctic sea ice cover
Author: Ian Eisenman: Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA and Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL043741, 2010 http://dx.doi.org/10.1029/2010GL043741