Image Credit: WoodForTrees.org
Guest Post By Werner Brozek, Edited By Just The Facts
RSS stands for Remote Sensing Systems, which is a satellite temperature data set similar to the University of Alabama – Huntsville (UAH) dataset that John Christy and Roy Spencer manage. Information about RSS can be found at here and the data set can be found here.
The plot of the number on the left column from November 1, 1996 to October 31, 2013 can be found in the graph at the head of his article and here. When the “Raw data” is clicked, we see that for 204 months, the slope is = -0.000122111 per year. I wish to make it perfectly clear that the focus is not on the magnitude of the negative number since this number is zero for all intents and purposes. The only thing that is noteworthy is that the slope is not positive.
And of course, 204 months is equal to 17 years. In the “Separating signal and noise in atmospheric temperature changes: The importance of timescale” Benjamin Santer et al. stated that:
“Our results show that temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature.”
I am sure that I will be corrected if I am wrong, but in plain English, my interpretation of this statement is as follows:
“There is a lot of noise in the climate system and it is quite possible that the noise can mask the effects of man-made carbon dioxide for a period of time. However if the slope is zero for 17 years, then we cannot blame noise any more but we have to face the facts that we humans do not affect the climate to any great extent.”
Is that reasonably accurate interpretation?
Richard Courtney offered a very interesting perspective in a comment previously:
“The Santer statement says that a period of at least 17 years is needed to see an anthropogenic effect. It is a political statement because “at least 17 years” could be any length of time longer than 17 years. It is not a scientific statement because it is not falsifiable.
However, if the Santer statement is claimed to be a scientific statement then any period longer than 17 years would indicate an anthropogenic effect. So, a 17-year period of no discernible global warming would indicate no anthropogenic global warming.
In my opinion, Santer made a political statement so it should be answered with a political response: i.e. it should be insisted that he said 17 years of no global warming means no anthropogenic global warming because any anthropogenic effect would have been observed.
Santer made his petard and he should be hoisted on it.”
Some may wonder why I am ignoring UAH. In response, I would just say that while UAH does not have a slope of 0 over the last 17 years, within the error bars of statistical significance, it is indeed possible for UAH to have a slope of 0 for this period of time. Nick Stokes’ Trend Viewer page shows: “CI from -0.384 to 2.353“. So while a larger trend cannot be ruled out, a slope of 0 is certainly possible according to climate science criteria for statistical significance.
You may be interested in how the other data sets compare over this same 17 year period. My recent post Statistical Significances – How Long Is “The Pause”? (Now Includes September Data) offers an in depth analysis and below is the plot for five other data sets. In addition to the RSS plot using all points for RSS and its slope line, I have just drawn the slope lines for the other five and offset them so they all start at the point where RSS starts in November 1996.
It is interesting to note that over this same 17 year period, the largest slope is that of UAH with 0.009/year or less than 1 degree C/century. That is certainly nothing to be alarmed about.