Thursday, February 19, 2009

"Missing" Arctic Sea Ice Found!

[Updated 22 Feb 2009]

One of the strongest pieces of evidence for the truth of Global Warming has been the reports of reduction in Arctic Sea Ice. According to the chart, published on 16 January 2009 by the National Snow and Ice Data Center (NSIDC), we have lost about one million square kilometers of Arctic Sea Ice extent in the 2008-2009 winter compared to the average extent for the winters of 1979-2000.

The solid gray line is the average for 1979-2000. The dashed green line is for the 2006-2007 winter and the blue line is reported data for the 2008-2009 winter. (NSIDC is funded by NASA/NOAA/NSF)

Have a look at the chart and notice a sudden, drastic drop of almost 1 MSq KM reported for the second week of February 2009. Watts Up noticed that additional drop and questioned it on 16 February 2009.

NSIDC checked and issued a statement dated February 18, 2009 admitting that "sensor drift" due to issues with one channel of the satellite sensor had caused an error of half a million square kilometers and that error has existed at least since early January:

NSIDC - National Snow and Ice Data Center

Arctic Sea Ice News & Analysis

Satellite sensor errors cause data outage

As some of our readers have already noticed, there was a significant problem with the daily sea ice data images on February 16. The problem arose from a malfunction of the satellite sensor we use for our daily sea ice products. Upon further investigation, we discovered that starting around early January, an error known as sensor drift caused a slowly growing underestimation of Arctic sea ice extent. The underestimation reached approximately 500,000 square kilometers (193,000 square miles) by mid-February. Sensor drift, although infrequent, does occasionally occur and it is one of the things that we account for during quality control measures prior to archiving the data. See below for more details.

We have removed the most recent data and are investigating alternative data sources that will provide correct results. It is not clear when we will have data back online, but we are working to resolve the issue as quickly as possible. ...

On February 16, 2009, as emails came in from puzzled readers, it became clear that there was a significant problem—sea-ice-covered regions were showing up as open ocean. The problem stemmed from a failure of the sea ice algorithm caused by degradation of one of the DMSP F15 sensor channels. Upon further investigation, we found that data quality had begun to degrade over the month preceding the catastrophic failure. As a result, our processes underestimated total sea ice extent for the affected period. Based on comparisons with sea ice extent derived from the NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, this underestimation grew from a negligible amount in early January to about 500,000 square kilometers (193,000 square miles) by mid-February ...

While dramatic, the underestimated values were not outside of expected variability until Monday, February 16. Although we believe that data prior to early January are reliable, we will conduct a full quality check in the coming days.

Sensor drift is a perfect but unfortunate example of the problems encountered in near-real-time analysis. We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice, which is based on the the consistent, quality-controlled data archive discussed above.

We are actively investigating how to address the problem. Since we are not receiving good DMSP SSM/I data at the present time, we have temporarily discontinued daily updates. We will restart the data stream as soon as possible.

Anthony Watts, who runs the Watts Up website wrote: "...I applaud NSIDC for recognizing the problem and posting a complete and detailed summary today."
[I added the RED and BLUE annotation on the above chart. I believe the sensor error first occured in December and continued until the drastic drop reported February 16th. The dashed BLUE curve is my estimate of what the true Arctic Sea Ice extent will turn out to be when the data is reconstructed from alternative sources.]

Despite this recent sensor drift, I believe a significant part of Arctic Sea Ice loss over the past several decades is almost certainly real. It is due to actual warming of the Earth.

We need to watch the Arctic Sea Ice over the coming years. If, as I hope, we see a stabilization or an increase in ice cover over a period of years, that will be a sign Global Warming has stabilized, at least for a while. That would bolster the argument that "It's the Sun, stupid."

This sensor drift error reminds me of the bias in temperature data. Could it be that measurements showing a sharp increase in CO2 are also biased by urban locations or other factors?

We now know for sure the mistaken correlation is causation Al Gore "hockey stick" assumption that rising CO2 leads rising temperature is unfounded in the ice core data.

However, if human activities plus the current warming cycle have actually raised global CO2 levels by a third since the 1700's, with 10% in the past forty years, that cannot be good for the longer term and we need to take action on carbon.

Ira Glickstein


Ira Glickstein said...

I updated this posting today to indicate my estimate of what the true Arctic Sea Ice extent will turn out to have been when the "sensor drift" error is corrected using data from other sources.

It appears (to me) that the sensor error began in December 2008 and continued until it was discovered due to a drastic drop reported 16 February 2009 and publicly acknowledged by NSIDC 18 February 2009.

Assuming the data from last winter (2007-2008) is correct, the Arctic Sea Ice has increased by about 0.5 MSq KM since last year and is now within 0.5 MSq KM of the 1979-2000 average. That means Arctic Sea Ice extent is only about 3% below the 1979-2000 average.

BOTTOM LINE: Arctic Sea Ice extent is down from the average, but is recovering a bit. If the recovery next year is equal to the recovery experienced this year, Arctic Sea Ice extent will be back to the average levels experienced over the past few decades.

Ira Glickstein

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