In anticipation of the first SEARCH Sea Ice Outlook report for 2010 (a synthesis report that describes the September sea ice predictions by several teams of scientists) I'll be posting a few short articles with summaries of predictions by scientists and knowledgeable laymen. I'm kicking off with Ronald W. Lindsay and Jinlun Zhang, both scientists from the Polar Science Center of the Applied Physics Laboratory at the University of Washington.
The reason I'm starting off with their prediction is because it's partly based on the prediction model called PIOMAS (Pan-Arctic Ice-Ocean Modeling and Assimilation System). I already knew about the model through its ominous volume reconstruction and the controversy it has been causing in some quarters (more about that when I discuss this prediction next time). The other reason is that Zhang has this nifty picture on his web page that makes my blog post look more interesting (click to enlarge):
As Ron Lindsay explains on his web page:
The model uses the observed air temperature, wind, clouds, and precipitation to estimate maps of the ice motion, ice thickness distribution, and ocean temperatures and currents for past years, up to and including the most recent month.
It seemed to work fairly well using historical data. However the summer of 2007 showed a tremendous loss of sea ice and the predictions from this method were way too conservative. This has led me to think that the statistical relationships between the ice extent and the state of the ice and ocean are changing rapidly and the past relationships cannot be a reliable guide to the future. However the most recent years are used to improve the model fits, so that extreme years such as 2007 are now included in the prediction.
And thus Lindsay predicts average extent in September to be 4.44 +/- 0.39 million square km. According to Lindsay his colleague Zhang uses 'quite a different method' for his prediction, which currently is 4.7 million square km. Mind you, these predictions are updated at the end of each month. For instance, at the end of April Linday's (very educated) guess was a September sea ice extent of 5.12 +/- 0.42 million sq km.
To put these predictions in perspective, these were the September average minimum sea ice extents in previous years according to IARC-JAXA:
2006: 5.91 million square km
2007: 4.38 million square km
2008: 4.83 million square km
2009: 5.38 million square km
Both scientists stress that "predicting ice conditions months in advance is a challenging problem for Arctic scientists". I think it's good to repeat this as there are a lot of prejudices circulating the web regarding climate scientists. As Lindsay says:
The exact thickness of the ice in spring that might survive depends on the location and on the air temperatures and cloud cover during the summer, both of which are not possible to predict more than a week or so into the future. Also, the ice extent is strongly dependent on the winds, as we saw in the summer of 2007. It is not possible to accurately predict the strength and direction of the winds months in advance. Depending on the air pressure patterns, the winds may or may not herd the remaining ice to one side of the basin, thus reducing the extent. What we do know is that the reduced ice thickness of recent years will lead to much more variability in the fall ice area and extent because the open water created during the summer is more sensitive to the initial ice conditions and the amount of melt. We still have a lot to learn about seasonal ice prediction.
The purpose of the seasonal predictions of arctic sea ice is for scientific research and education only. There are many uncertainties with the predictions and the results must be viewed with caution.
I think these predictions are on the conservative side (especially Zhang's). But hey, what do I know? I'm just an alarmist with no talent for numbers. Besides, it's only normal that polar scientists have probably become more careful after the shocker of 2007 and the following 'recoveries' in 2008 and 2009. We'll see if Lindsay's and Zhang's predictions change at the end of this month.
UPDATE: I've contacted Ron W Lindsay and Jinlun Zhang to follow up on GFW's comment that both are "giving September average predictions, not Sept minimum".
The answer: "My prediction is for the September average ice extent as reported by the Sea Ice Index. But Jinlun's is for the September average as calculated by the model."
I've updated the minima accordingly. Thanks, GFW!