Well tonight I get the great pleasure of redoing a post in the face of an inconvenient truth. To add insult to injury the error in my ways was pointed out by none other than my favorite liberal – Tamino who pointed out this section of the NSIDC data center. How I missed it in the hours I spent reading the site is beyond me. He did owe me one, at least we know he’s reading.
Note that unlike ice extent, the Arctic values for ice area do not include the area near the pole not imaged by the sensor (the “pole hole”). This area is 1.19 million square kilometers for SMMR (from the beginning of the series through June 1987) and 0.31 million square kilometers for SSM/I (from July 1987 to present). Therefore, there is a discontinuity in the “area” data values in this file at the June/July 1987 boundary.
This means that the sea ice area prior to 1987 was actually 0.88 million kilometers higher than the dataset indicated (if we assume 100% filled). Why it isn’t corrected in the data is due to the fact that the actual fill level is less than 100%. This results in an exaggerated downslope. Anyway here’s the new graphs (with a somewhat exaggerated downslope).
Here’s an image from the IUIC cryosphere page first which shows global trend.
Here’s the link check it out yourself. This isn’t that different from my original post but there is some down slope.
———————–Results from my exaggerated correction are below. ——————————–
Raw data looks like this after adding 880000 km^2 to the raw data before 1987.
A much more substantial downslope, value of – 37520 km^2/year or 1,050,000 km^2 over the 29 ish years. For the bootstrap algorithm the graph is below.
Bootstrap raw data above shows a reduced downslope of -26522 Km^2 per year or 740,000km^2 reduction.
The anomalies should be used instead for slope calculation because they clean up end point bias.
The slope from the nasateam plot was -40845 km^2/yr and the slope from the preferred bootstrap algorithm was -32037 km^2/year.
It was great that Watts up picked up my previous post followed by the disappointment of my huge mistake. Anyway this slope isn’t very strong but it is real, the arctic ice loss is greater than the gain in the southern hemisphere after the corrections are added in. It will be interesting to see how this changes when the increased area of 2008 data is added back into the curve.