Bad Science: NSIDC disappears Arctic sea ice extent going back years

Bad Science: NSIDC disappears Arctic sea ice extent going back years

http://ift.tt/2CMBbnk

From the “Arctic is screaming louder thanks to Mark Serreze and his adjustment shenanigans” department, I don’t think this is going to fly. Some of the adjustments are as much as 1.2 million square kilometers of sea ice, which is as much as some yearly variations. -Anthony

Guest essay Tom Wiita

I came across this month’s page posted at the NSIDC web site detailing the sea ice findings for the current month. It mentioned a revision to the way NSIDC calculates the sea ice area which was made last month. Curious, I went to last month’s page to check it out.

As a veteran NSIDC-watcher, before reading the page I made a falsifiable prediction bet with myself. I bet that this change in computation method increased the rate of decline of arctic sea ice compared to the rate of decline calculated under the old method. If the rate was greater, I win. If the rate of decline was lower, I lose and my prediction is falsified. You know, like in real science. This time I’m applying it to a social science study, of the behavior of NSIDC.

Would you believe it, I won my bet!

Here’s the link to the page:

http://ift.tt/2B7qOJQ

And here’s the relevant section describing the change copied straight off their public web site:

“Revised computation of the monthly mean extent

clip_image001

Figure 6. This chart compares the monthly October Arctic sea ice extents generated from the old (black dashed line) and the new (solid black line) averaging method. Sea Ice Index data. About the data
Credit: National Snow and Ice Data Center
High-resolution image

We have updated the way the monthly average sea ice extent is calculated in the NSIDC Sea Ice Index, the source for our sea ice extent estimates. The monthly average total extent (and area) are now computed as an average of the daily values over the month. Historically, the monthly mean sea ice extent has been calculated based on the monthly mean averaged sea ice concentration field. While there is a rationale for both approaches, the new method is more intuitive and eliminates unusual and unexpected results in months when there is rapid ice growth and retreat. Most of the new monthly mean extents are smaller than the previous values with a mean extent difference between -0.45+0.24 and -0.23+0.16 million square kilometers for the Arctic and Antarctic, respectively. The largest differences for the Arctic occur during the month of October due to the rapid ice growth rates typical at that time of year, with the largest difference of -1.20 million square kilometers in October 2012. Changes in rankings and trends were much smaller because the new method tends to affect all years of a given month in a similar manner. October is also the month with the largest trend difference, increasing in magnitude from -7.4 percent per decade to -9.3 percent per decade. Changes in Arctic trends for other months are much smaller.

Similarly, in the Antarctic, differences in averaging methods results in the largest changes during the month of December when the ice cover is rapidly receding. The largest difference of -1.27 million square kilometers occurs in December 1981. The largest changes in the trends are for January and December with a change in value from +2.7 to +3.5 and +1.2 to +1.9 percent per decade, respectively. For more detailed information on the impacts of the revised averaging methods on trends and rankings, please see NSIDC Special Report 19.”

Let me just point out a couple of things that stood out to me in the explanation above.

  • First, the bet-winning difference is that sea ice decline goes from 7.4% per decade to 9.3% per decade. Mark Serreze will be so happy – the arctic is screaming 1.9% louder per decade.
  • Second, all the values are lower after the revision. Every single one. “It’s worse than we thought!”, worse than we measured, worse than we reported to the world, worse, worse, worse. This has got to be one of the largest classic “worse than we thought” examples driven solely by a change in methods. They’re still after all looking at the exact same satellite pictures.
  • Third, look at the magnitudes of some of those differences. I mean, we missed that there were 1.2 MILLION fewer square kilometers of sea ice than we thought? Only 5 years ago in 2012? And we’ve been tracking this since 1979? And this is settled science? Come on!

Now, to be fair, the computation change giveth and the computation change taketh away.

Antarctic sea ice extent is growing faster after this change. But of course, as usual, they put anti-narrative results someplace safe, like into Antarctic sea ice growth, where they’ve always had a problem and already have multiple explanations/excuses: climate change is causing that, too; it’s going to turn around real soon, just you wait; ozone hole changes; more fresh water melting and freezing; at least West Antarctica is warming fast so something fits the narrative down there, etc.

Happy New Year to all!

Superforest,Climate Change

via Watts Up With That? http://ift.tt/1Viafi3

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