Has Arctic sea ice returned to normal?
What the science says...
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Arctic sea ice has been steadily thinning, even in the last few years while the surface ice (eg - sea ice extent) increased slightly. Consequently, the total amount of Arctic sea ice in 2008 and 2009 are the lowest on record. |
Climate Myth...
Arctic sea ice has recovered
"Those who have been following NSIDC and JAXA sea ice plots have noted that this has been an extraordinary year so far, with Arctic sea ice hitting the “normal” line on some datasets. ...
As of today,JAXA shows that we have more ice than any time on this date for the past 8 years of Aqua satellite measurement for this AMSRE dataset." (Anthony Watts, 22 April 2010)
When people talk about the state of Arctic sea ice, they most commonly refer to sea ice extent. This is the area of ocean where there is at least some sea ice (the most common cut-off is 15%). Sea ice extent shows a strong seasonal cycle as Arctic ice melts in the summer, reaching a minimum in September, then refreezes in the winter, peaking in March. Temperature is the main factor driving changes in sea ice extent, although other factors like wind patterns and cloudiness play a part. While sea ice extent has been steadily declining in recent decades, it fell to a record low in 2007 due to a combination of factors.
Figure 1: Sea ice extent with trend from 1953 onwards.
Sea ice extent gives us a reasonable indication of the amount of Arctic sea ice but does have its limitations. Extent tells us about the state of the sea ice at the ocean's surface, not what's happening below. A better metric for the total amount of sea ice is, well, the actual total amount of sea ice, measured by sea ice volume. Satellite radar altimetry (Giles 2008) and satellite laser altimetry (Kwok 2009) find that Arctic sea ice has been thinning, even in 2008 and 2009 when sea ice extent showed a slight recovery from the 2007 minimum. So while some claimed Arctic sea ice was recovering after 2007, the total volume of Arctic Sea ice through 2008 and 2009 were the lowest on record (Maslowski 2010, Tschudi 2010).
Figure 2: Continuously updated Arctic Sea Ice Volume Anomaly Polar Ice Center.
Currently, websites such as Watts Up With That are using sea ice extent in 2010 to claim Arctic sea ice has returned back to normal. A few days ago, Watts claimed that we had "more ice than any time on this date for the past 8 years". On the contrary, in March 2010, the total Arctic sea ice volume was 20,300 km3 - the lowest March value for total sea ice volume over the 1979-2009 period. Those who claim Arctic sea ice has returned to normal are focussing at the thin shell at the top and neglecting the steadily thinning sea ice below.
Intermediate rebuttal written by Daniel Bailey
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
Last updated on 21 October 2016 by MichaelK. View Archives
The volume chart above relies on the PIOMAS model. The model seems fine for predicting the summer minimum near the beginning of the melt season. See for example, the predictions for 2008: http://psc.apl.washington.edu/IDAO/seasonal_outlook.html Here they made an essentially correct prediction of substantially higher ice in Sept 2008 than Sept 2007. During the previous winter (2007-2008) they wrote a paper predicting the 2008 summer ice extent: LINK In this paper they predicted less ice than 2007 (a new record low) provided that weather forcings (not part of their model) remained substantially similar to 2007. Apparently they did not because the prediction was wrong. Unfortunately I have yet to find a followup paper explaining why the prediction was wrong. The paper emphasizes the use of thickness in the model as a major part of the prediction of extent. But if the thickness is wrong, then the predicted extent would also be wrong. Likewise, if the thickness is wrong in hindcasts when thickness was not measured extensively, then hindcasts of volume would also be invalid. I believe that caveat belongs on fig 2 above.
No, No, everything's OK with Arctic ice (kidding). Steven Goddard has a plot on his site showing that recently, there was the "Most Ice Gain Ever Recorded". What the plot seems to show is sea ice area change from the summer minimum to the cold season maximum. If the summer minimum extent is in a general, pronounced, downward direction, but spring max ice extent is holding steady or decreasing much less slowly it seems maybe the plot could reflect reality. But of course he's misusing that reality to imply something that is not true: i.e there's no "problem", by only highlighting a fraction of the story and then counting on his readers lack of curiosity and predjudices to make the incorrect assumption that arctic is is just fine - instead of for example seeing that the graph would represent the replacement of multiyear-age ice with one year old ice, among other things. "Skeptics", sheesh.
The most recent PIOMAS current ice volume anomaly graphic (31 January 2013) suggests to me that the Arctic Ocean is beginning to behave much more like a seasonally frozen lake or pond than a permanently frozen large expanse of ocean that melts around the edges. Note in particular the annual pattern in the graphed data from the 2010 maximum to the end of January, 2013:
http://psc.apl.washington.edu/wordpress/wp-content/uploads/schweiger/ice_volume/BPIOMASIceVolumeAnomalyCurrentV2.png?%3C?php%20echo%20time%28%29%20?
Yes, quite striking. Far be it from my place to criticize (because I'm way too ignorant) but the pattern of the last handful of years makes me wonder if we're overestimating the volume of ice left in the Arctic ocean. Those excursions just leap out at the eye.
doug,
I'm no expert either, but I trust that the recent volume calculations are fine. But I do wonder if the visible bouncing might be due to the shift to satellite observations which might possibly be better at recording the last stages of the summer melt season. That said, I think the explanation for the plunges is that there is now too little year-round ice both in terms of volume and area to keep the Arctic basin functioning as a year-round freezer. In other words, when most of the Arctic Ocean remained ice-covered throughout the melt season, the summer lows in ice area were reached by a fairly steady and slow process of melt around the edges and from below and this helped keep the volume loss low because the ice lid was still mostly in place. The last few melt cycles seem to simply reveal that the thin ice that does manage to form each winter is almost completely melting away with relative ease each summer--and then some of the old ice is also lost, hence the overall decline.
We need to remember that in previous years a fairly signficant portion of each winter's new ice survived to live another year, but that is no longer happening. I'd say that the magnitude of the annual range in volume is going to become even more dramatic--with much lower lows and gradually lower highs going forward until the summer ice volume bottoms out, whereupon the seasonally frozen pond/lake comparison will be very clear.
I'm curious about the relative temperatures of the ice in the pre-1980 days and more recently. I suspect that the current season's ice of the new Arctic is on average warmer, thanks to the influence of the ocean water beneath it and the relatively warmer air above it, at the start of the melt season than the old season's ice cover, which included more multiyear ice and had a colder atmosphere above it and potentially colder water below it, would have been.
It will be intersting to see if the climate models can explain thr 60% growth in artic ice this summer:
Link
[DB] Debunked here.
I doubt if climate models can explain the 2013 regression toward the mean, dadown. Why? Because big CMIP5 regime climate models aren't really designed for short-term projections. Modeling hasn't done well with Arctic sea ice in general. Note that we're a good 60 years ahead of the CMIP3 ensemble model mean for extent. In other words, Arctic sea ice could stabilize for half a century and the ice would still be ahead of its projected loss.
I'm curious, though: what does the 2013 melt season mean to you? I mean, what conclusions do you draw from it?
What I would like to know is why the ESA is not publishing a constantly updated graph of ice volume from cryosat as NSIDC does on ice extent. The weather patterns we have had in the summer of 2013 have a tendency to spread ice out (coriolis) and anything over 15% ice cover is recorded by NSIDC as full coverage. The increase in ice extent may be an reading glitch, at least to some extent. The ice volume results should clear up by how much the ice has actually increased between the middle of Sept 2012 and 2013 but the ESA seems oddly reluctant to tell us what their results are.
William, ice volume is not measured directly but calculated via the PIOMAS model. This is done monthly. You can get details here
...and US government shutdown is making data they need unavailable delaying the run.
Just wondering how the dismissives will fit this news into their "60% recovery" meme. Nah, they won't, they'll just quit talking about it.
Arctic Sea Ice Sits at Record Low for Mid-February - Climate Central