I admitted this might well be true. In my first cut for a short term fit, I’d limited myself to finding the best fit based on daily sea ice extent only and using only 1 predictor. This results in fits like the ones discussed in my previous NH Ice Extent Update<\/a>. <\/p>\n As I would like to improve that model by considering current ice area, I asked for a link to daily<\/i> NH ice area data. Neven pointed me to the Cryosphere Today<\/a> NH ice area data starting in 1970. Yesterday, I fiddled around to find the best predictor of the 7-day smooth JAXA minimum ice extent using limiting analysis to data since 1979. For ice extent, I used a merge of JAXA and NASA-GSFC. For ice area I used the Cryosphere today.<\/p>\n Once I had the data, I needed to think of candidate models to test. Currently, loads of people are trying to predict the NH Ice Extent minimum, and each discussed statistical models with the predictors based on different notions of what ought<\/i> to plausibly predict ice extent or ice melt rate. My initial goal is to consider candidate models that use one<\/i> predictor to predict the ice extent. That is: For now, I am avoiding multiple regressions. <\/p>\n With the available data, I computed the corrected Aikake criteria (AICc) for simple linear regressions for the following candidate models: <\/p>\n Based on AICc, of the three candidate models, predicting remaining extent loss as a function of the amount of vulnerable ice is the most efficient. Note that I find CRANDALS is correct that the current area gives a better prediction of the NH Ice Extent minimum– though I suspect as we near the actual minimum this must change. In the limit that we reach the minimum in the ice extent, the current ice extent must give a very good prediction! Still, currently: the best predictor is amount of vulnerable ice, the second best is area. <\/p>\n The fit based on vulnerable ice is shown below: The (+) indicates extent loss, that if achieved will result in a tie with the 2010 ice extent. The (x) indicates the extent loss that will result in a tie with the 2007 minimum. Both fall inside the \u00c2\u00b195% uncertainty intervals indicating that, according to this model, we may well see a new record low NH ice extent, or we may see the NH ice extent above that seen in 2010. Based on this model, the probability of a new low is estimated at 7% while the probability of a NH ice extent that exceeds 2010’s value is 28%. These are noted in black in the lower right hand corner of the figure. <\/p>\n Some of you will note that other probabilities are listed in blue. The second set of probabilities takes into account that while the “vulnerable ice” model appears to explain the past data better than the other two models, it is not sufficiently better to discount that possibility that the other models are in reality better predictors. Taking predictions of the other models into account, I estimate the probability of a new minimum at 9%. I will discuss the estimate based on the other two fits and how I weighted the two estimates in a future post planned within 2 days.<\/p>\n If you have other methods of predicting the current ice, or know of other troves of daily data, point me to them. Right now I know lots of people are fascinated by the horserace, and I like to quantify what I think is going to happen. Even if I guess wrong, I enjoy this more than just looking at the JAXA chart. <\/p>\n Links to data sources:<\/b><\/p>\n Time for the scheduled Wednesday NH ice update which includes the new method I concocted to predict the minimum. Based on my full new method, my best estimate of the 7 day minimum ice extent is currently 4.64 million km^2 and the probability of breaking the breaking the 2007 sea ice minimum is approximately 9%. … Continue reading NH Ice Update & Vulnerable Ice Method<\/span> \n
\n![\"\"](\"http:\/\/rankexploits.com\/musings\/wp-content\/uploads\/2011\/08\/PredictNHIceLoss-500x500.png\" "\\"PredictNHIceLoss\\"")
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\nThe open black circles are data for remaining losses as a function of the amount of vulnerable ice. Note that greater losses are correlated with larger amounts of vulnerable ice. The solid blue line indicates the best fit estimate for the remaining extent loss based on the current amount of vulnerable ice; the dashed lines indicate the \u00c2\u00b195% scatter about the mean assuming the residuals are normally distributed (which they appear not to be). The filled orange circle indicates best estimate of the ice loss rate based on the current amount of vulnerable ice (i.e. a remaining loss of 1.55 million square km); the open circles indicate the \u00c2\u00b195% confidence intervals based on scatter about the best fit curve and including the uncertainty in the trend and constant term for the model. <\/p>\n\n