Arguments
Has Arctic sea ice returned to normal?
Posted on 24 April 2010 by John Cook
An argument gaining popularity in 2010 is that Arctic sea ice has recovered from its long-term decline. Winter sea-ice extent bounced back strongly in the cold Arctic winter of 2010. Anthony Watts tells us that Arctic sea ice is returning to normal. However, this argument only looks at one piece of the puzzle while neglecting the full picture of the Arctic sea ice. Consequently, I've added a new rebuttal to the argument 'Arctic sea ice has recovered' (the 108th skeptic argument). This is basically a simplified version of Peter Hogarth's comprehensive review of peer-reviewed research into Arctic sea ice (and also includes useful information from the comments).
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.
http://psc.apl.washington.edu/zhang/IDAO/index.html
It includes forecasts for the Bering Sea and the whole Arctic. It looks like the model is at least underestimating the ice extent as of today. It'll be interesting to see how this works out.
If I understand this right the issue with sea ice extent is in regards the lower albedo of open sea during the summer months, right? Winter sea ice extent has little effect on albedo because the arctic is mostly in darkness. My question is, are the folks at WUWT being disingenuous to make any claims about sea ice extent in March when winter sea ice extent is going to have very little negative feedback?
GOSH NO!!! Because This NASA page from October of 2007, after the record summer low, explains how the lower "perennial" ice during the previous two winters combined with unusual wind patterns is what led to the record low. Also, NASS specifically states in their article that the March 2007 ice was the lowest ever for that month, so, in turn, NASA knows that the March Ice extent, which leads to perennial ice, is very important. What is going on is that many, including NASA - see YouTube, made predictions that the Arctic Ice was on a one way downhill slide because of feedbacks caused by open water, but just like the stock market and other things in nature (think Hurricanes after Katrina) nature has a way of fooling us all. We ALL just have to wait and see what happens. Things have a habit of reversing themselves and it is VERY IMPORTANT that artctic ice recovered in 2008 from the 2007 low and even recovered more in 2009 and is showing signs of continuing that recovery, it is what it is.
In this sense sea ice extent is measured, volume is not measured, not even calculated. These values are based on a computational model, heavily interlinked with other models. It is extremely difficult to verify such a thing.
However, they have a Seasonal Ensemble Forecasts of Arctic Sea Ice from April 2 to September 26, 2010 in three days steps made at the end of March (for scientific research and education only). I have made a backup, just in case.
In five months we can check if sea ice extent prediction is correct or not.
That is, the model is falsifiable. We can put more faith into ice volume reconstructions provided the ice extent prediction in fact will not be falsified. The September 2010 arctic sea ice extent is predicted to be 5.3 million square kilometers. We'll see.
robhon, in addition to albedo not being much of an issue during the arctic Winter it needs to be understood that sea ice extent is not DIRECTLY determinative of albedo. Sea ice area, the total surface area of ice floating in the ocean, determines albedo. This differs from extent in that extent is not the area of the ice itself, but rather the area of the ocean which is at least 15% covered with ice. So the extent can be as much as 1 / 0.15 = 667% as great as the ice area. This means that minor fluctuations in extent may or may not tell us anything about albedo... the extent could have changed because the area of the ice did OR because the ice was more or less spread out. This is one of the reasons why extent is really only useful for determining long term trends and making statements about 'recovery' based on minor variations in a couple of years are not just 'disingenuous' but clearly unfounded.
I'm actually asking less about the disingenuousness of WUWT and more about the lack of negative feedback because winter ice extent occurs mostly during the 24 hr darkness of winter.
I'm not suggesting that the winter ice extent isn't important - it's a relevant data point - but with regards to climate change winter ice extent is going to offer very little of what one might hope for: Increased albedo and some negative feedback.
(FWIW - We should ALL be hoping that there are more negative feedbacks out there than science seems to be currently finding.)
The layer below newly formed sea ice initially gets more saline but then tend to sink due to an increase in density. This contributes to the stratification of the Arctic Ocean.
The solidification temperature of sea water decreases by about 0.28 °C for every 5 PSU increase in salinity.
Sea ice melting may play a role as a CO2 sink. When ice melts the resulting water is depleted in CO2 and then can absorb more of it from the atmosphere.
A new paper in Nature used the latest ERA reanalysis product (called ERA-interim) to study the possible causes of the well known polar amplification.
They found that the impact of sea ice reduction is the largest contribution to the effect, more than atmospheric transport which is commonly believed to be dominant. They also considered humidity and cloud cover as possible causes.
One of the improvements of ERA-interim reanalysis is a more realistic troposheric temperature derived from satellite based irradiance measurements, which overcomes the lack of land based temperature measurements.
you may have noticed the meaning of the last three letters of the acronym PIOMAS: Modeling and Assimilation System. This means that it is not a pure model for projection; instead, measured relevant weather data are used to calculate actual ice volume. Projection ability relies on the quality of the weather data input and eventual failings do not disprove the ability to assess current ice volume.
Assuming no trivial errors in the model, the only way to disprove its calculation ability is with independent direct measurements of ice volume.
And it intersected it at a steep slope. Compared to 2007, the 2007 extent was limited the whole time and followed the curve pattern of the 30 year average. This year, the decline is much steeper than the 30 year curve.
How shall we hide THIS decline?
http://nsidc.org/data/seaice_index/images/daily_images/N_stddev_timeseries.png
(usual caveats about weather is not climate apply, and of course I am just eye-balling the graph.
For those who complain that 30 years isn't long enough – here is a graph that incorporates data back to 1900.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seasonal.extent.1900-2007.jpg
indeed they show the comparison with ICEsat for 2003-2007 here.
Martin Hartley, a member of the team, said the condition of the ice was unpleasantly bad.
“We spent a couple of days walking on ice that was three or four inches thick with no other thicker ice around, which was a big surprise to us,” he told the news conference.
“On more than one occasion we came across enormous areas of very thin ice, which is quite stressful to travel on. We came across open water which we had to swim across.”
At one point an ice floe the team’s tent was moored on broke apart, although no one was injured.
Last month explorers at the team’s ice base some 680 miles further south reported a three-minute rain shower, which they described as a freak event.
Arctic team reports unusual conditions near Pole
Team also reported rapid drift rates, far higher than anticipated, so perhaps we're looking at another 2007 where wind and warmth combined to make an excursion more noticeable than other years in a downward trend?
I haven't found any followup on their 1 year predictions for 2008, probably because they realize there are too many weather variables that are outside the scope of the model. Looks like the best use of the model is to run it in the spring to predict the fall minimum. The 2010 prediction is here http://psc.apl.washington.edu/zhang/IDAO/seasonal_outlook.html and is for 5.3m sq km, slightly less than 2009.