April 06, 2010
By Randall Hoven
There is an entity called the National Snow and Ice Data Center. If you go to its web site, you can find data and plots of sea ice extent. In particular, you can find the size of the Arctic ice cap, or what the NSIDC calls Northern Hemisphere sea ice. The graph shown on April 2, 2010 is reproduced below.
The data points in this chart reflect the extent of northern hemisphere sea ice in March of each year. The chart indicates that the arctic ice cap is melting - at a rate of 2.6% per decade (about 0.41 million square kilometers). At that rate, the polar ice cap would be gone in 385 years.
Such data have a lot of folks dismissing the CRUgate shenanigans as not all that relevant. Who cares about temperature data when you have the Arctic ice cap staring you in the face? For example, Katie Couric said, "A picture is worth a thousand emails and pictures of the polar ice caps show a 20% decrease since 1979."
First off, the above graph shows only an 8% decrease over the last 31 years, not a 20% decrease. So Katie would seem to have exaggerated.
But things get really interesting if you look at NSIDC's raw data, which come from the National Ocean and Atmospheric Administration (NOAA). You will notice that the above chart is of sea ice "extent." The data actually come in two versions: "extent" and "area," which are not quite the same. Here is how the NSIDC explains it.
"Important Note: The ‘extent' column includes the area near the pole not
imaged by the sensor. It is assumed to be entirely ice covered with at least
15% concentration. However, the ‘area' column excludes the area not imaged
by the sensor. 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."
My reading of those "important" words is that the only thing really measured by satellites was "area." Yet the plot showed "extent," something more than was measured. And the difference is something they "assumed." (If you have a better explanation of that "Important Note," please enlighten me.)
What were the differences? From the above words from NSIDC, you would think the differences would be constant offsets (1.19 million sq km from 1979 through June of 1987, and 0.31 million since). But the actual differences in the data file were not constant at all; they varied between 1.93 and 3.42 million sq km.
Why is the area of an assumed region included in the NSIDC's graph? More importantly, why does that assumed, non-measured, area vary from year to year and month to month in no apparent pattern?
The NSIDC does not provide a plot of the one thing that is measured: area. But I do, below, all based on the raw data provided at NSIDC's web site.
Using the raw data from NSIDC, I was able to reproduce its results for "extent." My calculations using the raw data showed a decline of 2.6% per decade, just as NSIDC said. So far, so good. (Or bad, depending on your point of view.)
However, the "area" is a different story. Just by eyeball, no trend is apparent. In fact, calculations say it is growing 0.3% per decade!
That is simply astounding. The Arctic sea ice that is actually measured by imaging sensors is growing, not shrinking at all. Shout it from the rooftops: we are saved!
Actually, the rate of growth is statistically insignificant, meaning a statistician would say it is neither growing nor shrinking; it just bobs up and down randomly. More good news: no coming ice age either.
All the above data was only for the month of March. What about other months? I tabulate below the growth rates (% per decade) for each of the months of the year.
Northern Hemisphere Sea Ice Growth 1978-2010, by Month
As a Percentage of the 1979-2000 Average
Growth of "Extent"
Growth of "Area"
You see that "extent" always shows more shrinkage than "area." In the months of maximum sea ice, February and March, the area trend is upward. And for winter months generally, December through May, any trend in area is statistically insignificant. For summer months, July through October, the trend is downward and statistically significant.
Katie Couric should have used the month of September as her example. In three decades, the Arctic sea ice "extent" shrank by 34%. She could make such claims while stating, truthfully, that the data come from NSIDC/NOAA and the trend is statistically significant. It's science.
If she had wanted to stretch the truth even further, she could have compared September of 1980 (extent of 7.85 million sq km) to September of 2007 (extent of 4.3 million sq km). That's a decline of 45%, almost half! (Katie needs a better cherry picker.)
Let's look more closely at those summer months. Below is the graph for September, the month showing the most shrinkage.
Again, the red line represents "area," the only thing actually measured. A downward trend is evident to the eyeball. But look closely and that downward trend is fairly recent, say since 2000. Indeed, the calculated trend was slightly upward through 2001. That is, the entire decline is explained by measurements since 2002, a time span of just eight years.
We are told by climate scientists themselves to ignore short-term anomalies. If we do, then even the more alarming ice cap shrinkage numbers, which were only for the summer months in the first place, disappear as well; they are short-term blips. In fact, September's sea ice area has gone up in the most recent two years of data.
Moreover, the verb "measured" is overly simplistic. The numbers result from computer algorithms working with satellite images. NSDIC has a section of its documentation called "Error Sources."
"There are a number of algorithms in use that convert channel brightness temperatures to sea ice concentration. All perform slightly differently under varying weather and ice conditions. Relatively few papers were published that compare algorithms or compare results with validation data... In summer, passive microwave overestimates open water by a larger amount, as the instrument cannot distinguish open water between ice floes with melt ponds on the floes, and other factors such as the ice-snow interface come into play (Comiso and Kwok 1996) and (Fetterer and Untersteiner 1998). This makes it difficult to interpret trends and anomalies for the summer months."
Well how about that? The very months where we found the most apparent shrinkage were the months that are the most "difficult to interpret trends and anomalies" and where the error would tend to underestimate ice.
This little Northern Hemisphere sea ice example captures so much of the climate change tempest in microcosm.
- When presenting data, the "scientists" include an unexplained adjustment to the measured data. In this case, the adjustments explain the entire evidence for Arctic ice cap shrinkage in winter months.
- Measurement processes depend on computer algorithms with scant validation -- "few papers were published that compare algorithms or compare results with validation data."
- Using only measured data, and all the data, there are no alarming trends. Winter months show no ice cap shrinkage at all. While there is shrinkage in summer months, that shrinkage is only evident in the last eight years, a time span too short to make a long-term conclusion, and in the months of least confidence in measurement techniques.
- The data allow cherry-picking. A Katie Couric, if she were cleverer, could say the Arctic ice cap shrank almost in half in the last three decades. On the other hand, I could say it grew 6% in that time period. We would both be telling the truth, by comparing cherry-picked months and years.
And all this was only for the north polar ice cap. The south one was more obviously growing over the last three decades. The Katie Courics of the world completely ignore that one.
And remember, even if we could clearly show that the planet is getting warmer, we would still need to show that such warming is bad, that it is caused by man and that the best cure is drastic cuts in fossil fuel usage. We are not even through step one of such an analysis.
By the way, I have not received a penny from Big Oil. But Big Oil can contact me at firstname.lastname@example.org.
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